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import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class Servlet1 extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        // Get the requested parameters （ Materials for handling affairs ） see         String username=request.getParameter("username");        System.out.println(" stay Servlet1（ Counter 1） View parameters （ material ）"+username);        // Set domain data ( Stamp the material , And deliver it to Servlet2（ Counter 2） Go to check )        request.setAttribute("key1", " Counter 1 Chapter of ");        // Asking directions ：Servlet2 How can we go there?         /**         *  The request must be forwarded with a slant / start ,/  The diagonal bar indicates that the address is http://ip:port/ project name /    Mapping to idea Medium is web Catalog          */        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/servlet2");        // trend Servlet2( Counter 2)        requestDispatcher.forward(request, response);    }}

servlet2 Under the class ：

public class Servlet2 extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        // Get the requested parameters （ Materials for handling affairs ） see         String username=request.getParameter("username");        System.out.println(" stay Servlet2（ Counter 2） View parameters （ material ）"+username);        // Check counter 1 Is there a seal         Object key1 = request.getAttribute("key1");        System.out.println(" Counter 1 Whether there is a chapter ："+key1);        // Deal with your own business         System.out.println("Servlet2 Deal with your own business ");    }}

Run access http://localhost:8080/03_servlet/servlet1

Running results ：

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Add parameters in the access bar ? These are all parameters

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Enter ：

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The characteristics of request forwarding

1、 The browser address bar has not changed （ It has always been the name of the project /servlet1）

2、 They try to ask

3、 Can be Shared Request Data in domain ( Domain data can be accessed throughout the project )

4、 It can be forwarded to WEB-INF Under the table of contents (WEB-INF Protected by the server , Not through the client （ browser ） Direct access can be accessed indirectly through resources in the server )

5、 Cannot access resources outside the project ( Because he found it under the project , You can't visit anything that doesn't exist under the project )

In the class Servlet1 in

Address access ：

   RequestDispatcher requestDispatcher = request.getRequestDispatcher("/WEB-INF/form.html");

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base label

The demo program cannot jump back

Create a class ForwardC Inherit HttpServlet class

public class ForwardC extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        System.out.println(" After Forward Program ");        req.getRequestDispatcher("/a/b/c.html").forward(req, resp);    }}

stay web.xml Middle configuration

  <servlet>        <servlet-name>ForwardC</servlet-name>        <servlet-class>com.servlet.ForwardC</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>ForwardC</servlet-name>        <url-pattern>/forwardC</url-pattern>    </servlet-mapping>

stay web The directory is created as shown in the figure

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stay c Write... In the directory

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title> This is a c page </title>  </head><body><a href="../../index.html"> Back to the home page </a></body></html>

stay index.html The write

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>Title</title></head><body> This is a web Under the index.html<br><a href="a/b/c.html">a/b/c.html</a><br><a href="http://localhost:8080/03_servlet/forwardC"> Request forwarding ：a/b/c.html</a></body></html>

After running ：

We talked about that before , Only write the project name, and the default access index page

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We found that clicking both up and down can successfully jump

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Although they all succeeded in jumping , But the address is obviously different , Because we are c.html The following is ../../index.html,

Running results ：

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In place analysis ：

The former ( first ),localhost:8080/03_servlet/a/b/c.html, after ../../ Jump to web Under the project , Just right web There are index.html, So it will jump successfully .

the latter ( the second ),localhost:8080/03_servlet/forwardC, after ../../ Jump to src Under the table of contents , and src Obviously, there is no index.html page , So it will fail .（ Structure is ：src/com/servlet/Forward）

Icon ：

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When we join base After label , The browser will use this base The label is the final address .

base Labels are usually added on title under

  <base href="http://localhost:8080/03_servlet/a/b/c.html">

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title> This is a c page </title>   <base href="http://localhost:8080/03_servlet/a/b/c.html"></head><body><a href="../../index.html"> Back to the home page </a></body></html>

This solves the problem that the latter cannot be transferred to the home page .

Web Relative path and absolute path in

stay javaWeb in , Paths are divided into relative paths and absolute paths ：

Relative paths ：

.     Represents the current directory
..          Represents the directory above
Resource name           Represents the current directory / Resource name

Absolute path ：

http://ip:port/ Project path / Resource path

web in / Different meanings of inclined rod

stay web in / A diagonal bar is an absolute path .

/ If the diagonal bar is parsed by the browser , The address you get is ：http://ip:port/

<a href="/"> The meaning of diagonal bar </a>

/ If the diagonal bar is parsed by the server , The address you get is ：http://ip:port/ Project path
1、<url-pattern>/servlet1<url-pattern>
2、servletContext.getRealPath("/");
3、request.getRequestDispatcher("/")

A special case ：response.sendRediect("/"); Send the diagonal bar to the browser for analysis , obtain http://ip:port/

HttpServletResponse class

HttpServletResponse The role of classes

HttpServletResponse Classes and HttpServRequest Similar to class . Every time I ask to come in ,Tomcat The server will create a Response Object passed to Servlet Program to use ,HttpServletRequest Indicates the information from ,HttpServletResponse Information that represents all responses , If we need to set the information returned to the client , Both can pass HttpServletResponse Object to set

Description of two output streams

Byte stream getOutputStream(); Commonly used for downloading （ Passing binary data ）
Character stream getWriter(); It is often used to return a string （ Commonly used ）

Two streams can only use one at a time . Otherwise, the report will be wrong

Return data to the client

Create a class ResponIOServlet：

import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.io.PrintWriter;public class ResponseIOServlet extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        PrintWriter writer=response.getWriter();        writer.write("AiQingShuiXingL");    }}

web.xml To configure , After running :

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Chinese code scrambling

Set up response.setCharacterEncoding("GBK"); It can solve the problem of Chinese garbled code displayed in the browser

The first way ：

public class ResponseIOServlet extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println(response.getCharacterEncoding());// The default character set is ISO-8859-1, No Chinese support       // Set the character set to GBK       response.setCharacterEncoding("GBK");        PrintWriter writer=response.getWriter();        writer.write(" Love wakes up ");    }

The second way ：

public class ResponseIOServlet extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println(response.getCharacterEncoding());// The default character set is ISO-8859-1, No Chinese support             // Set the character set to UTF—8        response.setCharacterEncoding("UTF-8");        // Tell the browser to also set UTF-8 that will do         response.setHeader("Content-Type", "text/html;charset=UTF-8");        PrintWriter writer=response.getWriter();        writer.write(" Love wakes up ");    }}

The third way ：

public class ResponseIOServlet extends HttpServlet {    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println(response.getCharacterEncoding());// The default character set is ISO-8859-1, No Chinese support // It must be used before getting the stream object , Otherwise it will not work         response.setContentType("text/html;charset=UTF-8");        PrintWriter writer=response.getWriter();        writer.write(" Love wakes up ");    }}

request redirections

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The first way

Create two classes response1 and response2

response1

import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class Response1 extends HttpServlet{    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        // Set response status code 302, Indicates redirection ( Has moved to a new place )        resp.setStatus(302);        // Set the response header , Explain where the new address is         resp.setHeader("Location","http://localhost:8080/03_servlet/response2");    }}

response2

import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class Response2 extends HttpServlet{    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {       resp.getWriter().write("hello response2");    }}

web.xml To configure Configure access path

    <servlet>        <servlet-name>Response1</servlet-name>        <servlet-class>com.servlet.Response1</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>Response1</servlet-name>        <url-pattern>/response1</url-pattern>    </servlet-mapping>    <servlet>        <servlet-name>Response2</servlet-name>        <servlet-class>com.servlet.Response2</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>Response2</servlet-name>        <url-pattern>/response2</url-pattern>    </servlet-mapping>

Running results ：

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Characteristics of request redirection

1、 The browser address bar will change
2、 It's two requests （ The first time is the old address , The second time is to relocate to a new address ）
3、 Cannot share Request Data in domain ( because Tomcat Each request will be sealed into an object , Two requests, so different objects )
4、 Cannot access WEB-INF Resources under ( Because it is also a request sent by the browser , Browsers can't directly access WEB-INF)
5、 You can access resources outside the project , Such as www.baidu.com

The second way

public class Response1 extends HttpServlet{    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        // The second method （ Set the new access address directly in brackets ）        resp.sendRedirect("http://www.baidu.com");    }}

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