hello2部分代码分析

/**

Copyright © 2014 Oracle and/or its affiliates. All rights reserved.
You may not modify, use, reproduce, or distribute this software except in
compliance with the terms of the License at:
https://github.com/javaee/tutorial-examples/LICENSE.txt
*/
package javaeetutorial.hello2;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**

This is a simple example of an HTTP Servlet. It responds to the GET method of
the HTTP protocol.
/
//
@WebServlet("/greeting")//路由配置
//这里使用注解来实现servlet到url的映射
/****
Servlet 3.0 的部署描述文件 web.xml 的顶层标签有一个 metadata-complete 属性，
该属性指定当前的部署描述文件是否是完全的。如果设置为 true，则容器在部署时将只依赖部署
描述文件，忽略所有的注解（同时也会跳过 web-fragment.xml 的扫描，亦即禁用可插性支持，）；
如果不配置该属性，或者将其设置为 false，则表示启用注解支持（和可插性支持）。应用注解方
便很多，不过现在都用集成spring等基本原始的servlet也不会多写了。
******/

public class GreetingServlet extends HttpServlet {

@Override
public void doGet(HttpServletRequest request,//重写httpservlet的doget方法，实现覆盖并用来处理get请求
        HttpServletResponse response)
        throws ServletException, IOException {

    response.setContentType("text/html");
    response.setBufferSize(8192);
    try (PrintWriter out = response.getWriter()) {
        out.println("<html lang=\"en\">"
                + "<head><title>Servlet Hello</title></head>");
        
        // then write the data of the response
        out.println("<body  bgcolor=\"#ffffff\">"
                + "<img src=\"resources/images/duke.waving.gif\" "
                + "alt=\"Duke waving his hand\">"
                + "<form method=\"get\">"
                + "<h2>Hello, my name is Duke. What's yours?</h2>"
                + "<input title=\"My name is: \" type=\"text\" "
                + "name=\"username\" size=\"25\"/>"
                + "<p></p>"
                + "<input type=\"submit\" value=\"Submit\"/>"
                + "<input type=\"reset\" value=\"Reset\"/>"
                + "</form>");
        
        String username = request.getParameter("username");//获取参数值
        if (username != null && username.length() > 0) {
            RequestDispatcher dispatcher =
                    getServletContext().getRequestDispatcher("/response");
					//获取url为/response的servlet作为转发的对象
            
            if (dispatcher != null) {
                dispatcher.include(request, response);
				//请求转发到response这个url对应的servlet
            }
        }
        out.println("</body></html>");
    }
}

@Override
public String getServletInfo() {
    return "The Hello servlet says hello.";

}

}

response.getWriter()返回的是PrintWriter，这是一个打印输出流。
response.getWriter().print(),不仅可以打印输出文本格式的（包括html标签），还可以将一个对象以默认的编码方式转换为二进制字节输出
response.getWriter().writer（）,只能打印输出文本格式的（包括html标签），不可以打印对象。
/**

You may not modify, use, reproduce, or distribute this software except in
compliance with the terms of the License at:
https://github.com/javaee/tutorial-examples/LICENSE.txt
*/
package javaeetutorial.hello2;

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

/**

This is a simple example of an HTTP Servlet. It responds to the GET
method of the HTTP protocol.
*/
@WebServlet("/response")//路由配置
public class ResponseServlet extends HttpServlet {

@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
try (PrintWriter out = response.getWriter()) { //获取输出对象，用于向页面写数据。返回的是一个printwriter对象
```
     String username = request.getParameter("username");
     if (username != null && username.length() > 0) {
         out.println("<h2>Hello, " + username + "!</h2>");
 		//开始写，与其类似的方法有个叫write
     }
 }
```
}

@Override
//getServletInfo() 方法是一个可选的方法，它提供有关 servlet 的信息，如作者、版本、版权。
//参考https://blog.csdn.net/qq_35624642/article/details/52473372
public String getServletInfo() {
return “The Response servlet says hello.”;

}
}

作者：慌逃
来源：CSDN
原文：https://blog.csdn.net/qq_36414969/article/details/88688458
版权声明：本文为博主原创文章，转载请附上博文链接！

hello2部分代码分析

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