javaEE：day2-Http头协议（doget/dopost）、转发与重定向、gzip压缩

http头协议

凡是以超链接登录的都是doget，表单请求可以设置请求头协议：doget、dopost

doget请求，可以直接用url带参数访问页面文件，如：http://127.0.0.1:8080/helloWeb_jun/login.jsp?name=aaa&pwd=123123123

而如果在表单中设置了method="post"的话则不能用上面的方式访问，必须是通过超链接点击访问。

浏览器的兼容： 我们要设置response.setContentType();用来设置头协议中的key，value。如：response.setContentType("text/html;charset=utf-8"); 来指定编码、文件类型等属性。

要做只能从当前页面跳转 判断拿到的referer是否是null，是否是从当前站点跳转过去的。`String refer=request.getHeader(“Referer”);

    String str = "";    if(refer==null){        str = "看点广告";    }else{        if(refer.contains("helloWeb")){            str = "<img src='./imgs/1.jpg'>";        }else{            str = "请从主页点击查看";        }    }`

转发与重定向：

重定向：相当于做两次请求 第一次请求是为了拿到资源的位置，第二次才是直接访问资源 没有第一次请求的request和response了

重定向用到的方法是

String path = "/helloWeb_jun/jsps/result.jsp";        response.sendRedirect(path);

转发：做一次请求 但是服务器内部会有一次转发，将请求转到资源 这时，保留原来的request和response 。

转发用到的方法是：

String path ="/jsps/result.jsp";        request.getRequestDispatcher(path).forward(request, response);

gzip压缩

以压缩格式，要设

        response.setContentType("text/html");        response.setHeader("Content-Encoding", "gzip");        response.setHeader("Content-length", ""+dest.length);

这里可以用setHeader的key，value来设置，也可以用response.setContentLength(dest.length); 来设置。

压缩

声明一点，如果是很小的文件，那么压缩之后反而会更大，因为压缩有开销。
用

        ByteArrayOutputStream array = new ByteArrayOutputStream();        GZIPOutputStream gout= new GZIPOutputStream(array);        gout.write(str);        gout.close();

来压缩，最后从array返回出去的就是压缩好的字节数组。

创建Servlet的几种方法：

1、直接new Servlet。—这种不需要手动配置xml

2、用implements Servlet ，然后补全来写。–这个需要自己手动去xml文档中配置

3、用extends HttpServlet 然后覆盖所需要的函数来写—这个需要手动去xml文档中配置

配置类似如下所示：

<servlet>    <servlet-name>imgServlet</servlet-name>    <servlet-class>cn.hncu.imgServlet.imgServlet</servlet-class></servlet>  <servlet-mapping>    <servlet-name>imgServlet</servlet-name>    <url-pattern>/servlet/imgServlet</url-pattern>  </servlet-mapping>

这个

<url-pattern>/servlet/imgServlet</url-pattern>

里面的/servlet/imgServlet就是我们在表单中的action的值。

最后，本文代码如下：

GzipServlet

package cn.hncu.imgServlet;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.OutputStream;import java.io.PrintWriter;import java.util.zip.GZIPOutputStream;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class GzipServlet 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 {        String msg = "dfjwoefjalsdjfowejflasjdfiowe放假偶尔发接哦我IQ耳机佛全文见佛千万IE附件分接欧文积分fjweofjwoefjwofj";        byte[] str = msg.getBytes();        //将字节数组压到array内存中去        ByteArrayOutputStream array = new ByteArrayOutputStream();        GZIPOutputStream gout= new GZIPOutputStream(array);        gout.write(str);        gout.close();        //将压缩后的数据从array中拿出        byte[] dest = array.toByteArray();        response.setContentType("text/html");        //response.setContentLength(dest.length);        response.setHeader("Content-Encoding", "gzip");        response.setHeader("Content-length", ""+dest.length);        OutputStream out = response.getOutputStream();        out.write(dest);        out.flush();        out.close();    }}

DispatcherServlet

package cn.hncu.imgServlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * 演示转发 * @author <a href="mailto:[e-mail]">军街</a> * * @version 1.0 2016-7-17 */public class DispatcherServlet extends HttpServlet {    @Override    protected void service(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        String path ="/jsps/result.jsp";        request.getRequestDispatcher(path).forward(request, response);    }}

RedirectServlet

package cn.hncu.imgServlet;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;/** * 演示重定向 * @author <a href="mailto:[e-mail]">军街</a> * * @version 1.0 2016-7-17 */public class RedirectServlet 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 {        //法1:        String path = "/helloWeb_jun/jsps/result.jsp";        response.sendRedirect(path);        //法2:        //response.setStatus(302);        //response.setHeader("Location", path);//      response.setCharacterEncoding("utf-8");    //  response.setCharacterEncoding("gbk");        //演示状态码//      response.setStatus(404);//      response.getWriter().write("not found找不到 ,good job");    }}

ShowPicServlet

package cn.hncu.imgServlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.Servlet;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class ShowPicServlet implements Servlet{    @Override    public void destroy() {    }    @Override    public ServletConfig getServletConfig() {        return null;    }    @Override    public String getServletInfo() {        return null;    }    @Override    public void init(ServletConfig arg0) throws ServletException {    }    @Override    public void service(ServletRequest arg0, ServletResponse arg1)            throws ServletException, IOException {        HttpServletRequest request = (HttpServletRequest) arg0;        HttpServletResponse response = (HttpServletResponse) arg1;        response.setContentType("text/html;charset=utf-8");        PrintWriter out = response.getWriter();        //String str = "<img src='./imgs/1.jpg'>";        //做只能从主页点击才能进入 靠单纯的url不能查看图片        //http://127.0.0.1:8080/helloWeb_jun/pic   ----看点广告        String refer=request.getHeader("Referer");        String str = "";        if(refer==null){            str = "看点广告";        }else{            if(refer.contains("helloWeb")){                str = "<img src='./imgs/1.jpg'>";            }else{                str = "请从主页点击查看";            }        }        out.write(str);    }}

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>  </head>  <body>    <a href="jspDay1/demo1.jsp">导向我的jsp文件</a> <br>    <hr/>    <!--以form表单提交 这种是在url中显示输入的-->    <!-- 默认的method是get -->    <!-- http://127.0.0.1:8080/helloWeb_jun/login.jsp?name=aaa&pwd=123123123 -->    <form action="login.jsp">        姓名:<input type="text" name="name"/><br/>        密码:<input type="text" name="pwd"/><br/>        <input type="submit" value="登录"/>    </form>    <!--以form表单提交 这种是在url中不显示输入的-->    <!-- http://127.0.0.1:8080/helloWeb_jun/login.jsp -->    <form action="login.jsp" method="post">        姓名:<input type="text" name="name"/><br/>        密码:<input type="text" name="pwd"/><br/>        <input type="submit" value="登录"/>    </form>    <br/>    <!--以超链接方式登录-->    <a href="http://127.0.0.1:8080/helloWeb_jun/login.jsp?name=cv&pwd=6666">以超链接方式登录</a><br/>    <br/>    <br/>    <hr/>    <a href="pic">查看美女图</a>    <br/>    <br/>    <hr/>    <h2>下面演示重定向和转发</h2>    <!-- 重定向：相当于做两次请求 第一次请求是为了拿到资源的位置，第二次才是直接访问资源  没有第一次请求的request和response了-->    <!-- 转发：做一次请求 但是服务器内部会有一次转发，将请求转到资源 这时，保留原来的request和response -->    <a href="redirect">重定向</a><br/>    <a href="dispatcher">转发</a><br/>    <hr/>    <h2>演示压缩gzip</h2>    <!-- http://127.0.0.1:8080/helloWeb_jun/ -->    <a href="gzip">压缩gzip</a>  </body></html>

result.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body>      <h1>这时重定向的最终页面</h1></body></html>