JavaWeb 初步

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1. Servlet快速入门

1.1. 编写servlet 类

入门:找Servlet所在包... 建立的工程必须web工程!! 自动导入javaee.jar类库!!

第一步: 创建普通java实现Servlet接口

第一种写法：

package cn.itcast.day01_tomcat.servlet;import java.io.IOException;import javax.servlet.Servlet;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class MyServlet1 implements Servlet{@Overridepublic void destroy() {// TODO Auto-generated method stub}@Overridepublic ServletConfig getServletConfig() {// TODO Auto-generated method stubreturn null;}@Overridepublic String getServletInfo() {// TODO Auto-generated method stubreturn null;}@Overridepublic void init(ServletConfig arg0) throws ServletException {// 表示  当前servlet对象被容器创建...该方法只执行一次.....System.out.println("hello ----init  初始化方法执行");}@Overridepublic void service(ServletRequest arg0, ServletResponse arg1)throws ServletException, IOException {//   浏览器请求一次  该方法就执行一次.....System.out.println("hello ----service  业务方法执行");}}

浏览器如何访问该servlet对象呢? http://localhost/day01_tomcat/

1: 该对象谁创建?

服务器端开发: 对象servlet组件由容器创建(tomcat)

2: 浏览器如何访问该资源?

当浏览器访问该资源的时候（http://localhost/day01_tomcat/）,容器执行该对象创建 ...对应Init 方法就会执行,,,,

第二步:配置web.xml

web.xml 是当前工程的主配置文件 ,

容器根据web.xml文件中的相关标签配置，自动创建该对象，并执行相关方法!!

标签:<servlet> <servlet-mapping>

<servlet-name>MyServlet1</servlet-name>

<servlet-class>cn.itcast.day01_tomcat.servlet.MyServlet1</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>MyServlet1</servlet-name>

<url-pattern>/servlet1</url-pattern>

</servlet-mapping>

<servlet-class>cn.itcast.day01_tomcat.servlet.MyServlet1</servlet-class>

右键类名选择 copy qualiedfied Name 即可!!，不要手写，容易出错！！！

Servlet接口

------ 实现类 GenericServlet ----- 子类 HttpServlet ---- 自定义Servlet 继承HttpServlet

第二种写法：

import java.io.IOException;import javax.servlet.GenericServlet;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;//  GenericServlet 对象不包含  具有http协议 api 的 public class MyServlet2 extends GenericServlet{@Overridepublic void service(ServletRequest req, ServletResponse res)throws ServletException, IOException {//   编写业务即可与    获取客户端浏览器getMethodSystem.out.println("------servlet2  ----");//   浏览器访问服务器....  ServletRequest  (该对象 接受 浏览器(客户端)发送请求参数  )//   ServletResponse  服务器通过 该对象给予 客户端 响应数据 ..}}

第三种写法：

分析

    public void service(ServletRequest req, ServletResponse res)        throws ServletException, IOException {        HttpServletRequest  request;        HttpServletResponse response;                try {            request = (HttpServletRequest) req;            response = (HttpServletResponse) res;        } catch (ClassCastException e) {            throw new ServletException("non-HTTP request or response");        }        service(request, response);    }

第三种写法实现：

package cn.itcast.day01_tomcat.servlet;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 MyServlet3 extends HttpServlet {    @Override    protected void service(HttpServletRequest req, HttpServletResponse resp)    throws ServletException, IOException {    //  浏览器的访问  请求方式... 7  种  get  post  service  方法 接受所有请求方式...      //  HttpServlet 类   重写GenericServlet 提供抽象service 方法  自定义了一个service方法     //  该方法里面 请求的方式 分类..根据浏览请求方式不同  调用不同的方法      // 自定义的 servlet   不用重写 service   直接重写  具体请求方式业务方法!!    String  value  = req.getMethod();    System.out.println(value+"-----");    }}

第四种实现方法：为了划分请求方式

因为HttpServelt中的已经帮我们区分了从浏览器发起的不同请求

protected void service(HttpServletRequest req, HttpServletResponse resp)        throws ServletException, IOException {        String method = req.getMethod();        if (method.equals(METHOD_GET)) {            long lastModified = getLastModified(req);            if (lastModified == -1) {                // servlet doesn't support if-modified-since, no reason                // to go through further expensive logic                doGet(req, resp);            } else {                long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);                if (ifModifiedSince < (lastModified / 1000 * 1000)) {                    // If the servlet mod time is later, call doGet()                    // Round down to the nearest second for a proper compare                    // A ifModifiedSince of -1 will always be less                    maybeSetLastModified(resp, lastModified);                    doGet(req, resp);                } else {                    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);                }            }        } else if (method.equals(METHOD_HEAD)) {            long lastModified = getLastModified(req);            maybeSetLastModified(resp, lastModified);            doHead(req, resp);        } else if (method.equals(METHOD_POST)) {            doPost(req, resp);                    } else if (method.equals(METHOD_PUT)) {            doPut(req, resp);                            } else if (method.equals(METHOD_DELETE)) {            doDelete(req, resp);                    } else if (method.equals(METHOD_OPTIONS)) {            doOptions(req,resp);                    } else if (method.equals(METHOD_TRACE)) {            doTrace(req,resp);                    } else {            //            // Note that this means NO servlet supports whatever            // method was requested, anywhere on this server.            //            String errMsg = lStrings.getString("http.method_not_implemented");            Object[] errArgs = new Object[1];            errArgs[0] = method;            errMsg = MessageFormat.format(errMsg, errArgs);                        resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);        }    }

package cn.itcast.day01_tomcat.servlet;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 MyServlet4 extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp)    throws ServletException, IOException {    //   该方法执行 只接受get请求...    System.out.println("----do get----");    }        @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp)    throws ServletException, IOException {    //   只接受Post请求...    System.out.println("----do post----");    }}

第五种：相同的业务，代码冗余。

package cn.itcast.day01_tomcat.servlet;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 MyServlet5 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doPost(req, resp);// get请求 业务方法由dopost执行}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {System.out.println("get---post");}}

第6种：用eclipse创建servlet，Name：Myservlet6

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 MyServlet6 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doPost(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {// 开始进行servlet代码开发吧System.out.println("servlet 6 ---");}}

第7种：优化模板

2014版本：

C:\Users\Administrator\AppData\Local\MyEclipse Professional 2014\plugins

修改 com.genuitec.eclipse.wizards_11.5.0.me201310291746.jar

2010版本：

C:\Users\lili\AppData\Local\MyEclipse\Common\plugins

修改Servlet.java种的doGet和doPost方法

用工具生产Servlet代码，以及web.xml种的配置

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