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[学习笔记]马士兵 Servlet & JSP(1.Servlet)
www.diybl.com 时间： 2010-05-22 作者：匿名编辑：Mr.阿布点击： 131 [ 评论 ]

1.HTTP协议基础测试（获取页面源代码）
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
/**
* HTTP协议基础测试
* 本程序将Tomcat首页的页面源代码拿下来
* 用此方法，我们可以将我们访问到的页面的内容都拿下来
* @author ykn
*
*/
public class HttpTest {
    public static void main(String[] args) {

        Socket s = null;
        PrintWriter pw = null;
        BufferedReader br = null;

        try {
            // 建立连接端口，s指向本地机器tomcat服务器端口上
            s = new Socket("127.0.0.1",8888);
            // 对于本程序而言是输出，则相当于是准备向tomcat服务器端口写请求
            pw = new PrintWriter(new OutputStreamWriter(s.getOutputStream()));
            // 请求访问页面（此处等同于访问http://localhost:8888/）
            pw.println("GET / HTTP/1.1");
            pw.println("Host: www.bjsxt.com");
            pw.println("Content-Type:text/html");
            pw.println("");
            // 上一句表示请求内容结束
            pw.flush();
            // 上面这一段用于本程序向Tomcat服务器发出访问请求（get）


            // 服务器端作出响应，对于本程序而言是输入
            br = new BufferedReader(new InputStreamReader(s.getInputStream()));
            String str = "";
            // 将服务器端的响应信息打印输出（即将http://localhost:8888/页面代码源文件中的内容输出）
            // 用此方法，我们可以将我们访问到的页面的内容都拿下来
            while((str = br.readLine()) != null) {
                System.out.println(str);
            }

        } catch (UnknownHostException e) {
            System.out.println("未知的主机异常。。。");
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("IO异常。。。");
            e.printStackTrace();
        } finally {
            try {
                if (br != null) {
                    br.close();
                    br = null;
                }
                if (pw != null) {
                    pw.close();
                    pw = null;
                }
                if (s != null) {
                    s.close();
                    s = null;
                }
            } catch (IOException e) {
                System.out.println("IO异常。。。");
                e.printStackTrace();
            }
        }
    }
}
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2.最简单的servlet示例
说明：
①将HelloWorldServlet .class拷贝到test\WEB-INF\classes目录下（test是项目名）
②在web.xml中添加对应的servlet处理语句：
    <servlet>
        <servlet-name>HW</servlet-name>
        <servlet-class>HelloWorldServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>HW</servlet-name>
        <url-pattern>/abc</url-pattern>
    </servlet-mapping>
③在URL地址栏中以http://localhost:8888/test/abc形式访问
④页面上显示结果：Hello World!
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 简单的servlet示例
* @author jukey
*
*/
public class HelloWorldServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=gb2312");
        PrintWriter out = response.getWriter();
        out.println("Hello World!");
    }

}

-----------------------------------------------------------------------------------------------------------------------------------
3.Servlet的生命周期测试
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet的生命周期
* @author jukey
*
*/
public class TestLifeCycleServlet extends HttpServlet {
    // 处理请求
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("doGet");
    }
    // 实例化
    // 注意：构造方法不能有返回值类型，连void也不行（否则就变成普通方法了）
    public TestLifeCycleServlet() {
        System.out.println("constructed");
    }

    // 退出服务
    public void destroy() {
        System.out.println("destory");
    }
    // 初始化
    public void init() throws ServletException {
        System.out.println("init");
    }
}
/*
测试结果（在tomcat服务器控制台窗口）：
constructed
init
doGet
*/

------------------------------------------------------------------------------------------------------------------------------------
4.读取指定的参数
①Threeparams.htm
<form id="form1" name="form1" method="post" action="servlet/Threeparams">
    <table width="343" border="1">
        <tr>
            <td width="92">param1</td>
            <td width="94"><input name="param1" type="text" id="param1"/></td>
        </tr>
        <tr>
            <td width="92">param2</td>
            <td width="94"><input name="param2" type="text" id="param2"/></td>
        </tr>
        <tr>
            <td width="92">param3</td>
            <td width="94"><input name="param3" type="text" id="param3"/></td>
        </tr>
        <tr>
            <td> </td>
            <td><input type="submit" value="提交"/></td>
        </tr>
    </table>
</form>
②ThreeParams.java
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 读取指定的参数
* @author jukey
*
*/
public class ThreeParams extends HttpServlet {
    // 参数在传递过程中，在URL地址栏中显示出来
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=gb2312");
        PrintWriter pw = response.getWriter();
        pw.println(request.getParameter("param1"));
        pw.println("<br>");
        pw.println(request.getParameter("param2"));
        pw.println("<br>");
        pw.println(request.getParameter("param3"));
        pw.println("<br>");
    }
    // 参数在传递过程中，在URL地址栏中隐藏了
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("doPost");
        // 调用doGet方法
        doGet(request,response);
    }
}
----------------------------------------------------------------------------------------------------------------------------------

5.读取所有的参数
①Showparameters.htm
<html>
    <head>
        <title>A sample show parameters</title>
    </head>
    <body>A sample show parameters

        <form method="post" action="servlet/ShowParameters">
            Item Number:<input type="text" name="itemNum"><br>
            Quantity:<input type="text" name="quantity"><br>
            Price each:<input type="text" name="price" value="$"><br>
            First Name:<input type="text" name="firstName"><br>
            Last Name:<input type="text" name="lastName"><br>
            Middle Initial:<input type="text" name="initial"><br>

            Shipping Address:<textarea name="address" row="3" cols="40"></textarea><br>
            Credit Card:<br>
            
              <input type="radio" name="cardType" value="Visa">Visa<br>
              <input type="radio" name="cardType" value="Master Card">Master Card<br>
              <input type="radio" name="cardType" value="Amex">Amex<br>
              <input type="radio" name="cardType" value="Discover">Discover<br>
              <input type="radio" name="cardType" value="Java SmartCard">Java SmartCard<br>
            
            Credit Card password:<input type="password" name="cardNum"><br>
            Repeat Credit Card password:<input type="password" name="cardNum"><br><br>

            <center><input type="submit" value="Submit Order"></center>

        </form>
    </body>
</html>
②ShowParameters.java
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 读取所有的参数
* @author jukey
*
*/
public class ShowParameters extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=gb2312");
        PrintWriter out = response.getWriter();

        String title = "Reading All Request Parameters";
        out.println("init");
        out.println("<html><head><title>读取所有参数</title></head>"
                + title
                + "\n" + "<table border=1 align=center>\n"
                + "<TH>Parameter Name<TH>Parameter Value(s)");

        // Returns an Enumeration of String objects containing the names of the parameters contained in this request.
        Enumeration paramNames = request.getParameterNames();
        // Tests if this enumeration contains more elements.
        while(paramNames.hasMoreElements()) {
            // Returns the next element of this enumeration if this enumeration object has at least one more element to provide.
            String paraName = (String)paramNames.nextElement();
            out.println("<tr><td>" + paraName + "\n<td>");
            // Returns an array of String objects containing all of the values the given request parameter has, or null if the parameter does not exist.
            // 注意参数paraName（变量）不能加双引号，否则就是找参数名叫paraName的对应值了。
            String[] paramValues = request.getParameterValues(paraName);
            // 这个参数只有一个值
            if(paramValues.length == 1) {
                String paramValue = paramValues[0];
                if(paramValue.length() == 0) {
                    out.println("<I>no value</I>");
                } else {
                    out.println(paramValue);
                }
            }else {
                // 这个参数有好几条值
                out.println("<UL>");
                for(int i = 0; i < paramValues.length; i++) {
                    out.println("<LI>" + paramValues[i]);
                }
                out.println("</UL>");
            }
        }
        out.println("</table>\n<body></html>");
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("doPost");
        doGet(request,response);
    }
}
--------------------------------------------------------------------------------------------------------------------------------------------
6.Cookies的设置和读取
①设置Cookie到客户端
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 设置Cookie到客户端
* @author jukey
*
*/
public class SetCookies extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 向客户端写入Cookie，共6个
        for(int i = 0; i < 3; i++) {
            // 3个没有设置时间的Cookie，属于本窗口及其子窗口
            Cookie cookie = new Cookie("Session-Cookie-" + i, "Cookie-Value-S" + i);
            response.addCookie(cookie);
            // 以下3个Cookie设置了时间（3600秒，1小时），属于文本，别的窗口也可以访问到这些Cookie
            cookie = new Cookie("Persistent-Cookie-" + i, "Cookie-Value-P" + i);
            cookie.setMaxAge(3600);
            response.addCookie(cookie);
        }

        response.setContentType("text/html;charset=gb2312");
        PrintWriter out = response.getWriter();
        String title = "Setting Cookies";
        out.println("<html><head><title>设置Cookie</title></head>"
                + "<body>" + title + "<br>"
                + "There are six cookies associates with this page.<br>"
                + "to see them,visit the <a href=\"ShowCookies\">\n"
                + "<code>ShowCookies</code> servlet</a>"
                + "</body></html>");
    }
}

②读取客户端的Cookies
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 读取客户端的Cookies
* @author jukey
*
*/
public class ShowCookies extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html;charset=gb2312");
        PrintWriter pw = response.getWriter();
        String title = "Active Cookies";
        pw.println("init");
        pw.println("<html><head><title>读取客户端</title></head>"
                + title
                + "\n" + "<table border=1 align=center>\n"
                + "<TH>Cookie Name<TH>Cookie Value" + "<br>");

        // 读取客户端的所有Cookie
        Cookie[] cookies = request.getCookies();
        if(cookies != null) {
            Cookie cookie;
            for(int i = 0; i < cookies.length; i++) {
                cookie = cookies[i];
                pw.println("<tr>\n" + "<td>" + cookie.getName() +"</td>\n"
                        + "<td>" + cookie.getValue() +"</td></tr>\n");
            }
        }
        pw.println("</table>\n<body><html>");
    }
}
--------------------------------------------------------------------------------------------------------------------------------------
7.Session的测试
①演示Servlet API中的session管理机制（常用方法）
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* 演示Servlet API中的session管理机制（常用方法）
* @author jukey
*
*/
public class SessionInfoServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        // Returns the current session associated with this request, or if the request does not have a session, creates one.
        HttpSession mySession = request.getSession(true);

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        String title = "Session Info Servlet";
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Session Info Servlet</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h3>Session Infomation</h3>");

        // Returns true if the client does not yet know about the session or if the client chooses not to join the session.
        out.println("New Session:" + mySession.isNew() + "<br>");
        // Returns a string containing the unique identifier assigned to this session.
        out.println("Session Id:" + mySession.getId() + "<br>");
        // Returns the time when this session was created, measured in milliseconds since midnight January 1, 1970 GMT.
        out.println("Session Create Time:" + new Date(mySession.getCreationTime()) + "<br>");
        out.println("Session Last Access Time:" + new Date(mySession.getLastAccessedTime()) + "<br>");

        out.println("<h3>Request Infomation</h3>");
        // Returns the session ID specified by the client.
        out.println("Session Id From Request:" + request.getRequestedSessionId() + "<br>");
        // Checks whether the requested session ID came in as a cookie.
        out.println("Session Id Via Cookie:" + request.isRequestedSessionIdFromCookie() + "<br>");
        // Checks whether the requested session ID came in as part of the request URL.
        out.println("Session Id Via URL:" + request.isRequestedSessionIdFromURL() + "<br>");
        // Checks whether the requested session ID is still valid.
        out.println("Valid Session Id:" + request.isRequestedSessionIdValid() + "<br>");

        out.println("<a href=" + response.encodeURL("SessionInfoServlet") + ">refresh</a>");
        out.println("</body></html>");
        out.close();
    }
}
②Session追踪
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* Session追踪
* 如果浏览器支持Cookie，创建Session的时候会把SessionId保存在Cookie中
* 否则必须自己编程使用URL重写的方式实现Session：response.encodeURL()
* @author jukey
*
*/
public class ShowSession extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html;charset=gb2312");
        PrintWriter out = response.getWriter();
        String str = "Session Tracking Example";
        String heading;

        // 如果会话已经存在，则返回一个HttpSession；否则创建一个新的
        HttpSession session = request.getSession(true);
        // 从当前session中读取属性accessCount的值
        Integer accessCount = (Integer)session.getAttribute("accessCount");
        if(accessCount == null) {
            accessCount = new Integer(0);
            heading = "Welcome newUser";
        } else {
            heading = "Welcome Back";
            accessCount = new Integer(accessCount.intValue() + 1);
        }
        // 向当前session中插入键（key，属性）值（value）对
        // Binds an object to this session, using the name specified.
        session.setAttribute("accessCount", accessCount);

        out.println("<html><head><title>Session追踪</title></head>"
                + "<body>" + heading + "<br>"
                + "<h2>Information on Your Session</h2><br>"
                + "\n" + "<table border=1 align=center>\n"
                + "<TH>Info Type<TH>Value" + "<br>"
                + "<tr>\n" + "<td>ID</td>\n"
                + "<td>" + session.getId() +"</td></tr>\n"
                + "<tr>\n" + "<td>CreatTime</td>\n"
                + "<td>" + new Date(session.getCreationTime()) +"</td></tr>\n"
                + "<tr>\n" + "<td>LastAccessTime</td>\n"
                + "<td>" + new Date(session.getLastAccessedTime()) +"</td></tr>\n"
                + "<tr>\n" + "<td>Number of Access</td>\n"
                + "<td>" + accessCount +"</td></tr>\n"
                + "</body></html>");
    }
}
--------------------------------------------------------------------------------------------------------------------------------
8.Application测试
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Application测试
* 用于保存整个web应用的生命周期内都可以访问的数据
* 可供多个不同窗口访问，可作为某一页面被总共访问次数的计数器（比如网站首页的访问量）
* @author jukey
*
*/
public class TestServletContext extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html;charset=gb2312");
        PrintWriter out = response.getWriter();

        // Returns a reference to the ServletContext in which this servlet is running.
        ServletContext application = this.getServletContext();
        // 从当前application中读取属性accessCount的值
        Integer accessCount = (Integer)application.getAttribute("accessCount");
        if(accessCount == null) {
            accessCount = new Integer(0);
        } else {
            accessCount = new Integer(accessCount.intValue() + 1);
        }
        // 向当前application中插入键（key，属性）值（value）对
        application.setAttribute("accessCount", accessCount);

        out.println("<html><head><title>ServletContext测试</title></head><br>"
                + "<body><td>" + accessCount +"</td>\n"
                + "</body></html>");

    }
}
---------------------------------------------------------------------------------------------------------------------------------------------
9.Servlet类本身位于包中的情况
package com.bjsxt.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet类本身位于包中的情况
* classes中要class文件及其各级目录一起放置
* web中如下设置：<servlet-class>com.bjsxt.servlet.HelloWorldServlet2</servlet-class>
* @author jukey
*
*/
public class HelloWorldServlet2 extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html;charset=gb2312");
        PrintWriter out = response.getWriter();
        out.println("Hello World!");

    }
}

--------------------------------------------------------------------------------------------------------------------------------
10.在Servlet中直接连接数据库，并查询显示信息
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 在Servlet中直接连接数据库，并查询显示信息
* 每个application都应该有自己的驱动包，放在各自项目的WEB-INF\lib\目录下
* @author jukey
*
*/
public class ShowRs extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        response.setContentType("text/html;charset=gb2312");
        PrintWriter out = response.getWriter();
        out.println("<table border=1>");
        out.println("<tr><td>Content:</td></tr>");
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost/bbs?user=root&password=mysql");
            stmt = conn.createStatement();
            String sql = "select * from article";
            rs = stmt.executeQuery(sql);
            while(rs.next()) {
                out.println("<tr>");
                out.println("<td>" + rs.getString("cont") + "</td>");
                out.println("</tr>");
            }
        } catch (SQLException ex) {
            ex.printStackTrace();
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
             if (rs != null) {
                 try {
                     rs.close();
                     rs = null;
                 } catch (SQLException sqlEx) {
                     sqlEx.printStackTrace();
                 }
             }
             if (stmt != null) {
                 try {
                     stmt.close();
                     stmt = null;
                 } catch (SQLException sqlEx) {
                     sqlEx.printStackTrace();
                 }
             }
             if (conn != null) {
                 try {
                     conn.close();
                     conn = null;
                 } catch (SQLException sqlEx) {
                     sqlEx.printStackTrace();
                 }
             }
        }
    }
}

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11.Servlet中使用专门的数据库操作类DB
①Servlet中使用专门的数据库操作类DB，这样，本程序就比前一个显得简单清楚
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet中使用专门的数据库操作类DB，这样，本程序就比前一个显得简单清楚
* DB类，专门跟数据库打交道，分工明确，各司其职
* @author jukey
*
*/
public class ShowRsUseBean extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html;charset=gb2312");
        PrintWriter out = response.getWriter();
        out.println("<table border=1>");
        out.println("<tr><td>Content:</td></tr>");

        // 直接调用DB中的静态方法来为本类服务
        Connection conn = DB.getConnection();
        Statement stmt = DB.getStatement(conn);
        String sql = "select * from article";
        ResultSet rs = DB.getResultSet(stmt, sql);

        try {
            while(rs.next()) {
                out.println("<tr>");
                out.println("<td>" + rs.getString("cont") + "</td>");
                out.println("</tr>");
            }
        } catch (SQLException e) {
            System.out.println("执行SQL遍历过程中出现了错误。。。");
            e.printStackTrace();
        } finally {
            // 直接调用DB中的静态方法来关闭一系列被打开的资源
            DB.close(rs);
            DB.close(stmt);
            DB.close(conn);
        }
    }
}

②专门跟数据库打交道的类
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
/**
* 专门跟数据库打交道的类
* @author ykn
*
*/
public class DB {
    // 获取连接
    public static Connection getConnection() {
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost/bbs?user=root&password=mysql");
        } catch (ClassNotFoundException e) {
            System.out.println("驱动程序未找到，请加入mysql.jdbc的驱动包。。。");
            e.printStackTrace();
        } catch (SQLException e) {
            System.out.println("执行数据库连接过程中出现了错误。。。");
            e.printStackTrace();
        }
        return conn;
    }

    // 获取表达式语句
    public static Statement getStatement(Connection conn) {
        Statement stmt = null;
        try {
            if (conn != null) {
                stmt = conn.createStatement();
            }
        } catch (SQLException e) {
            System.out.println("执行获取表达式语句过程中出现了错误。。。");
            e.printStackTrace();
        }
        return stmt;
    }

    // 获取查询的结果集
    public static ResultSet getResultSet(Statement stmt, String sql) {
        ResultSet rs = null;
        try {
            if (stmt != null) {
                rs = stmt.executeQuery(sql);
            }
        } catch (SQLException e) {
            System.out.println("执行查询过程中出现了错误。。。");
            e.printStackTrace();
        }
        return rs;
    }

    // 关闭连接
    public static void close(Connection conn) {
        try {
            if (conn != null) {
                conn.close();
                conn = null;
            }
        } catch (SQLException e) {
            System.out.println("执行关闭数据库连接过程中出现了错误。。。");
            e.printStackTrace();
        }
    }

    // 关闭表达式语句
    public static void close(Statement stmt) {
        try {
            if (stmt != null) {
                stmt.close();
                stmt = null;
            }
        } catch (SQLException e) {
            System.out.println("执行关闭表达式语句过程中出现了错误。。。");
            e.printStackTrace();
        }
    }

    // 关闭结果集
    public static void close(ResultSet rs) {
        try {
            if (rs != null) {
                rs.close();
                rs = null;
            }
        } catch (SQLException e) {
            System.out.println("执行关闭结果集过程中出现了错误。。。");
            e.printStackTrace();
        }
    }

[学习笔记]马士兵 Servlet & JSP(2.JSP)
www.diybl.com 时间： 2010-05-22 作者：匿名编辑：Mr.阿布点击： 34 [ 评论 ]

1.最简单的JSP
HelloWorld.jsp
<html>
    <head>
        <title>Hello</title>
        <body>
            <%
                out.println("Hello World!");
            %>
        </body>
    </head>
</html>
---------------------------------------------------------------------------------------------------------------------------------------
2.JSP中的全局变量和局部变量
AccessCounts.jsp
<html>
    <head>
        <title>JSP Declaration</title>
    </head>
    <body>
        <%!
            // 全局变量
            int accessCount = 0;
        %>

        <%
            // 局部变量
            int accessCount2 = 0;
        %>

        <h2>AccessCount:
            <br>Overall Variable:<%= ++accessCount %>
            <br>Local Variable:<%= ++accessCount2 %>
        </h2>

    </body>
</html>
测试结果：访问同一页面，每刷新一次，accessCount增1，accessCount2不变（每次出现一个新的局部变量）。
----------------------------------------------------------------------------------------------------------------------------------
3.注释、当前页面从URL中取背景色参数
BGColor.jsp
<html>
    <head>
        <title>Color Testing</title>
    </head>

    

    <%--
    JSP注释
    客户端看不见
    --%>


    <%
    //注释2
    /*
    注释3
    */
    // 将请求中参数bgColor的值拿过来，假如没有传这个参数，则值为null
    String bgColor = request.getParameter("bgColor");
    boolean hasColor;
    if(bgColor != null) {
        hasColor = true;
    } else {
        hasColor = false;
        bgColor = "white";
    }
    %>

        
    <body bgcolor="<%= bgColor%>">
    <h2 align="center">Color Testing</h2>

    <%
    if(hasColor) {
        out.println("You supplied a backgroud color of " + bgColor + ".");
    } else {
        out.println("Use Default backgroud color of white");
    }
    %>

    </body>
</html>

-----------------------------------------------------------------------------------------------------------------------------

4.表达式
Expressions.jsp
<html>
    <head>
        <title>JSP Expressions</title>
    </head>
    
    <body>
        <h2>JSP Expressions</h2>

    <UL>
        
        <LI>Current Time:<%= new java.util.Date().toLocaleString() %>
        <LI>Your HostName:<%= request.getRemoteHost() %>
        
        <LI>Your Session Id:<%= session.getId() %>
        <LI>The <code>testParam</code> from parameter:<%= request.getParameter("testParam") %>
    </UL>

    </body>
</html>
----------------------------------------------------------------------------------------------------------------------------------------
5.@page指示语句的测试
TestDirective.jsp
<%@page import="java.util.*" %>
<%@page contentType="text/html;charset=gb2312" %>
    
    
<%= new Date().toLocaleString() %>
<br><br>
<%
    out.println("你好！");
%>

--------------------------------------------------------------------------------------------------------------------------------
6.错误页跳转测试
①TestErr.jsp
<%@page errorPage="ErrPage.jsp" %>

<%
String str = "123abc";
int i = Integer.parseInt(str);
out.println("str= " + str + ",i= " + i);
%>
②ErrPage.jsp
<%@page contentType="text/html;charset=gb2312" %>
<%@page isErrorPage="true" %>

<html>
    <body text="red">
        错误信息：<%= exception.getMessage()%>
    </body>
</html>

-----------------------------------------------------------------------------------------------------------------------------
7.include指令”%@ include file“和include动作指令“jsp:include page”
前者是先包含进来再编译执行；后者是先各自编译执行再包含进来
①include.jsp
<html>
    <head>
        <title>include test</title>
    </head>

    <body bgcolor="white">
        <font color="red">
            The current time and date are:<br>
        
            <%@include file="date.jsp" %><br>
        
            <jsp:include page="date.jsp" flush="true" />
        </font>
    </body>
</html>
②date.jsp
<%@page import="java.util.*" %>
<%--a string representation of this date, using the locale conventions.--%>
<%= (new Date()).toLocaleString() %>
说明：以下转载自网络   http://blog.matrix.org.cn/rudy541/entry/200708162
jsp中两种包含文件的区别：
相同点：两者逗能包含一个页面
不同点：
区别1：
<jsp:include page="b.jsp" />（先执行，后包含）
此标签表示法：能动态区别加进来的是动态页面还是静态页面
对于静态页面则直接将资源包含(仅取其文本)。
对于动态页面则先处理各自资源，之后将处理过的结果包含在一起。
<%@ include file="b.jsp">
此指令表示：静态地包含页面，不管其内容如何，不过是静态页面还是动态页面都首先将页面的内容先加进来。
然后一起处理，再将所有内容发给客户端。
实例挑战：
有b.jsp页面
<%int i = 10 ;%>
<%=i%>
主界面a.jsp也有<%int i = 100 ;%>        <%=i%>
如果是加载<%@ include file="b.jsp">，则是先包含后执行，就会发现报错，i被重新定义，
但如果是加载<jsp:include page="b.jsp" />则是先执行结果，然后将结果包括到主页面。不会报错。
区别2：
<jsp:include page="b.jsp" />可以分开写成：
<jsp:include page="b.jsp" >
<jsp:param name="参数名" value="参数值"/>
</jsp:include>
这样就可以传递参数。

----------------------------------------------------------------------------------------------------------------------
8.两个数的乘除运算
①Compute.html
<html>
    <head>
        <title>Compute</title>
        <meta http-equiv="Content-Type" content="text/html;charset=gb2312">
    </head>
    
    <body bgcolor="#FFFFFF">
        <div align="center">
            <form method="post" action="Compute.jsp">
                <p>选择要做的运算：
                    <input type="radio" name="compute" value="division" checked>
                    除法
                    <input type="radio" name="compute" value="multiplication">
                    乘法
                </p>
                <p>被除数（被乘数）
                    <input type="text" name="value1">
                    除数（乘数）
                    <input type="text" name="value2">
                </p>
                <p>
                    <input type="submit" name="Submit" value="计算结果">
                </p>
            </form>
        </div>
    </body>
</html>
②Compute.jsp
<%@page language="java" %>
<%@page contentType="text/html;charset=gb2312" %>
<%
    // 将Compute.html页面输入的要进行计算的两个变量拿过来
    String value1 = request.getParameter("value1");
    String value2 = request.getParameter("value2");
%>
<% if("division".equals(request.getParameter("compute"))) { %>
    
        <jsp:include page="divide.jsp" flush="true">
            <jsp:param name="v1" value="<%=value1%>"/>
            <jsp:param name="v2" value="<%=value2%>"/>
        </jsp:include>
<%    } else { %>
        
        <%@include file="multiply.jsp" %>
<%    } %>

③multiply.jsp
<%@page contentType="text/html;charset=gb2312" %>
<html>
    <head>
        <title>Multiply</title>
    </head>
    <%--进行乘法计算的JSP--%>
    <body bgcolor="#FFFFFF">
        <center>
            <h1>
                <%
                    try{
                        float multiplicand = Float.parseFloat(request.getParameter("value1"));
                        float multiplicator = Float.parseFloat(request.getParameter("value2"));
                        double result = multiplicand*multiplicator;
                        out.println(multiplicand + "*" + multiplicator +" = " + result);
                    } catch(Exception e) {
                        out.println("不合法的乘数或被乘数");
                    }
                %>
            </h1>
        </center>
    </body>
</html>
④divide.jsp
<%@page contentType="text/html;charset=gb2312" %>
<html>
    <head>
        <title>Divide</title>
    </head>
    <%--进行除法计算的JSP--%>
    <body bgcolor="#FFFFFF">
        <center>
            <h1>
                <%
                    try{
                        float divident = Float.parseFloat(request.getParameter("v1"));
                        float divisor = Float.parseFloat(request.getParameter("v2"));
                        double result = divident/divisor;
                        %>
                        <%= result%>
                        <%
                    } catch(Exception e) {
                        out.println("不合法的除数或被除数");
                    }
                %>
            </h1>
        </center>
    </body>
</html>
----------------------------------------------------------------------------------------------------------------------------------
9.jsp:forward和response.sendRedirect
①最简单的jsp:forward
forward.jsp
<html>
    <head>
        <title>Forward Example</title>
    </head>
    
    <body bgcolor=red>
        Welcome to forward.jsp
        <%--直接跳转到forforward.jsp，这两个jsp用的是同一个request--%>
        <jsp:forward page="forforward.jsp" />
    </body>
</html>
forforward.jsp
<html>
    <head>
        <title>forforward.jsp</title>
    </head>

    <body bgcolor=blue>
        Welcome<br>
        Here is forforward.jsp
    </body>
</html>
②jsp:forward和response.sendRedirect的比较
forward1.jsp
<html>
    <head>
        <title>Forward Example</title>
    </head>

    <body bgcolor=red>
        Welcome to forward1.jsp
        <jsp:forward page="forforward1.jsp" >
            <jsp:param name="name" value="m" />
            <jsp:param name="oldName" value='<%= request.getParameter("name")%>' />
            <jsp:param name="roles" value="manager" />
        </jsp:forward>
    </body>
</html>
forforward1.jsp：和forward1.jsp使用的是同一个request（服务器跳转）
<html>
    <head>
        <title>forforward1.jsp</title>
    </head>

    <body bgcolor=blue>
        Welcome<br>
        Here is forforward1.jsp<br>
        <%= request.getParameter("name")%>
        <%= request.getParameter("oldName")%>
        <%= request.getParameter("roles")%>
        <%= request.getParameter("address")%>
    </body>
</html>
测试结果：
访问http://localhost:8888/test/forward/forward1.jsp?name=yyg&address=34527144231
结果：
Welcome
Here is forforward1.jsp
m yyg manager 34527144231
此时页面URL还是forward1.jsp，并没有跳转到forforward1.jsp，给用户的感觉还是刚才的页面在为自己服务。
说明：m 和manager 是forward1.jsp中传过来的；而yyg 和34527144231 是在URL中通过request传过来的。并且forward1.jsp中也没有address属性，这也从另一个角度说明了这两个jsp使用的是同一个request。

test.jsp：和forward1.jsp使用的是不同的request
说明：访问过http://localhost:8888/test/forward/test.jsp后，页面跳转成http://localhost:8888/test/forward/forforward1.jsp
这个过程中客户和服务器之间产生了两个request，并且test.jsp后跟参数并不能传递到forforward1.jsp（原因也很明显：两次是不同的request）
<%
response.sendRedirect("forforward1.jsp");
%>

---------------------------------------------------------------------------------------------------------------------------------------------
10.jsp:useBean
①CounterBean.java
package bean;
import java.io.Serializable;
/**
* 一个很普通的JavaBean
* @author jukey
*
*/
public class CounterBean implements Serializable {

    private int count = 0;
    public CounterBean() {}
    public int getCount() {
        count++;
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }
}
②test.jsp:JSP往JavaBean中设置值，从JavaBean中拿值
<%@page import="bean.*" %>
<%--
<%
    // 下面这个语句等同于<jsp:useBean id="cb" class="bean.CounterBean"></jsp:useBean>
    CounterBean cb = new CounterBean();
%>
--%>
<jsp:useBean id="cb" class="bean.CounterBean">
</jsp:useBean>
<font color="red" size="5">
    <%--将bean中存储的值拿出来--%>
    <%= cb.getCount()%>
</font>

<jsp:setProperty name="cb" property="count" value="25" />
    <%--cb.setCount(25)--%>


<jsp:getProperty name="cb" property="count" />
    <%--cb.getCount()--%>

以下是Bean的4种作用范围的测试：
③page有效（仅涵盖使用JavaBean的页面）
PageBean.jsp
<jsp:useBean id="counterBean" scope="page" class="bean.CounterBean" />

<html>
    <body>
        <h3>CounterBean scope="page" Example</h3>
        <b>count:</b> <%= counterBean.getCount()%>
    <%--上下两句效果一样--%>
        <jsp:getProperty name="counterBean" property="count"/>
    </body>
</html>
④request有效（有效范围仅限于使用JavaBean的请求）
RequestBean.jsp

<jsp:useBean id="counterBean" scope="request" class="bean.CounterBean" />

<%--
    bean.CounterBean counterBean = request.getAttribute("counterBean");
    if(counterBean == null) {
        counterBean = new bean.CounterBean();
        request.setAttribute("counterBean",counterBean);
    }
--%>

<html>
    <body>
        <h3>CounterBean scope="request" Example</h3>
    
        <% counterBean.setCount(100); %>
        <%--和RequestBean2.jsp用的是同一个request，也是同一个counterBean对象--%>
            
        <jsp:forward page="RequestBean2.jsp" />

            <%--和RequestBean2.jsp用的不是同一个request，也不是同一个counterBean对象--%>
                
                
        <%-- response.sendRedirect("RequestBean2.jsp"); --%>
    </body>
</html>

RequestBean2.jsp

<jsp:useBean id="counterBean" scope="request" class="bean.CounterBean" />

<html>
    <body>
        <h3>CounterBean scope="request" Example</h3>
        <b>count:</b> <%= counterBean.getCount()%>
    </body>
</html>

⑤Session有效（有效范围在用户整个连接过程中，整个会话阶段均有效）
SessionBean.jsp

<jsp:useBean id="counterBean" scope="session" class="bean.CounterBean" />

<%--
    // 这一段java代码等同于上面这句JSP语句
    bean.CounterBean counterBean = session.getAttribute("counterBean");
    if(counterBean == null) {
        counterBean = new bean.CounterBean();
        session.setAttribute("counterBean",counterBean);
    }
--%>
<html>
    <body>
        <h3>CounterBean scope="session" Example</h3>
        <b>count:</b> <%= counterBean.getCount()%>
    </body>
</html>

SessionBean2.jsp

<jsp:useBean id="counterBean" scope="session" class="bean.CounterBean" />

<html>
    <body>
        <h3>CounterBean scope="session" Example</h3>
        <b>count:</b> <%= counterBean.getCount()%>
    </body>
</html>

⑥application有效（有效范围涵盖整个应用程序，也就是对整个网站都有效）
可用于作为首页访问量的计数器
ApplicationBean.jsp

ApplicationBean2.jsp

<jsp:useBean id="counterBean" scope="application" class="bean.CounterBean" />

<html>
    <body>
        <h3>CounterBean scope="application" Example</h3>
        <b>count:</b> <%= counterBean.getCount()%>
    </body>
</html>
----------------------------------------------------------------------------------------------------------------------
11.jsp:setProperty和jsp:getProperty
①SaleEntry.jsp
<html>
    <head>
        <title>Using jsp:setProperty</title>
    </head>
    
    <body>
        <table border=5 align="center" >
            <tr><th class="title">
                Using jsp:setProperty
        </table>

        <jsp:useBean id="entry" class="bean.SaleEntry" />

        <%--从JSP向JavaBean中设值--%>

        <jsp:setProperty name="entry" property="itemID" value="<%= request.getParameter("itemID")%>" />
        <jsp:setProperty name="entry" property="numItems" param="numItems" />
        <jsp:setProperty name="entry" property="discountCode" param="discountCode" />

        <br>

        <table border=1 align="center" >
            <tr class="colored">
                <th>Item ID<th>Unit Price<th>Number Ordered<th>Total Price
            <tr align="right">
                <%--Jsp从JavaBean中取值--%>
                <td><jsp:getProperty name="entry" property="itemID" />
                <td>$<jsp:getProperty name="entry" property="itemCost" />
                <td><jsp:getProperty name="entry" property="numItems" />
                <td>$<jsp:getProperty name="entry" property="totalCost" />
        </table>
    </body>
</html>
②SaleEntry.java
package bean;
public class SaleEntry {

    private String itemID = "unknown";
    // 折扣
    private double discountCode = 1.0;
    private int numItems = 0;

    public double getDiscountCode() {
        return discountCode;
    }

    public void setDiscountCode(double discountCode) {
        this.discountCode = discountCode;
    }

    public String getItemID() {
        return itemID;
    }

    public void setItemID(String itemID) {
        this.itemID = itemID;
    }

    public int getNumItems() {
        return numItems;
    }

    public void setNumItems(int numItems) {
        this.numItems = numItems;
    }

    // 获取单价
    public double getItemCost() {
        double cost;
        if("a1234".equals(itemID)) {
            cost = 12.99 * getDiscountCode();
        } else {
            cost = -99;
        }
        return roundToPennies(cost);
    }

    // 计算到分位
    public double roundToPennies(double cost) {
        return (Math.floor(cost * 100) / 100.0);
    }

    // 计算总价格
    public double getTotalCost() {
        return (getItemCost() * getNumItems());
    }

}

-------------------------------------------------------------------------------------------------------------------------------------
12.HTML页面输入内容，提交给JSP文件，JSP将这些内容存入JavaBean，再从JavaBean中拿出来显示。
中间有个中文乱码的处理问题。
①SayHelloBean.html
<html>
    <head>
        <title>数据输入</title>
        <meta http-equiv="Content-Type" content="text/html;charset=gb2312">
    </head>

    <body bgcolor="#FFFFFF">
        <div align="center" >
            <p>请输入数据</p>
                <form method="post" action="SayHelloBean.jsp" >
                    <p>姓名
                        <input type="text" name="name">
                        性别
                        <select name="sex">
                            <option value="先生">先生</option>
                            <option value="女士">女士</option>
                        </select>
                    </p>
                    <p>
                        <input type="submit" name="Submit" value="提交">
                    </p>
                </form>
                <p> </p>
                <p> </p>
        </div>
    </body>
</html>

②SayHelloBean.jsp
<%@page language="java" import="bean.HelloBean;" %>
<%@page contentType="text/html;charset=gb2312" %>
<%--先将传过来的request中的字符编码格式设置成gbk，再取内容--%>
<% request.setCharacterEncoding("gbk"); %>
<jsp:useBean id="hello" class="bean.HelloBean" scope="request" >
    <%--通过*来设置所有属性和输入参数之间的关联，struts中大量运用--%>
        <jsp:setProperty name="hello" property="*" />
</jsp:useBean>

<html>
    <head>
        <title>HelloBean</title>
        <meta http-equiv="Content-Type" content="text/html;charset=gb2312">
    </head>

    <body bgcolor="#FFFFFF">
        <p> </p>
        <p align="center" >
            <font size="4">欢迎
                <font color="#0000FF">
                    <b>
                        <%--转码(终结解决方案)：将hello对象中name属性的值用ISO8859_1编码格式以字节数组拿出，再转化成gbk格式---%>
                        <%--= new String(hello.getName().getBytes("ISO8859_1"),"gbk")--%>
                    </b>
                </font>
                <%--转码(终结解决方案)：将hello对象中sex属性的值用ISO8859_1编码格式以字节数组拿出，再转化成gbk格式---%>
                <%--= new String(hello.getSex().getBytes("ISO8859_1"),"gbk")--%>
            </font>
        </p>
        <jsp:getProperty name="hello" property="name" />
        <jsp:getProperty name="hello" property="sex" />
    </body>
</html>

③HelloBean.java
package bean;
public class HelloBean {
    private String name = "";
    private String sex = "";

    public HelloBean() {}

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

}

[学习笔记]马士兵 Servlet & JSP(3.Servlet和JSP的通信)
www.diybl.com 时间： 2010-05-22 作者：匿名编辑：Mr.阿布点击： 92 [ 评论 ]

（1）从JSP调用Servlet可用<jsp:forward>，请求信息自动转到Servlet
FromJspToServlet.jsp
<html>
    <body bgcolor="green">
        
        <jsp:forward page="/servlet/ServletToJSP" />
    </body>
</html>

（2）从Servlet调用JSP可以使用RequestDispatcher接口的forward(req, resp)方法，请求信息需要显示传递
ServletToJSP.java

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletToJSP extends HttpServlet {
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        // 设置属性并将它分发给/servlet_jsp/ServletUseJsp.jsp处理
        resp.setContentType("text/html;charset=gb2312");
        req.setAttribute("servletName", "ServletToJSP");
        // RequestDispatcher getRequestDispatcher(String path):
        // Returns a RequestDispatcher object that acts as a wrapper for the resource located at the given path.
        getServletConfig().getServletContext().getRequestDispatcher("/servlet_jsp/ServletUseJsp.jsp").forward(req, resp);
    }
}

（3）ServletUseJsp.jsp
<%@page contentType="text/html;charset=gb2312" %>
<html>
    <meta context="text/html;charset=gb2312">
    <head>
        <title>Servlet使用JSP</title>
    </head>

    <body bgcolor="gray">
        <h2>Servlet使用JSP的例子</h2>
        <h2>这个页面是被Servlet调用的</h2>
    </body>
</html>

说明：以上相互调用也可以直接使用sendRedirect