sevlet 对包中hello2部分文件的分析_综合

关于servlet处理参考：https://www.cnblogs.com/jerrice/p/6724060.html

/**

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 responseout.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>");//这里需要注意，action没有指明地址时，submit会把当前url当做action地址//所以这个httpservlet有两个作用String username = request.getParameter("username");//获取前端传来的参数值.//这里的request应该在servlet容器中//通过容器传递给当前httpservletif (username != null && username.length() > 0) {RequestDispatcher dispatcher =getServletContext().getRequestDispatcher("/response");//通过当前context//获取url为/response的servlet作为一个dispatcher资源if (dispatcher != null) {dispatcher.include(request, response);//将当前的request,response资源包含到dispatcher用于响应//其实就是在dispatcher中通过request获得username//然后在response中添加了hello这几句话//（这里的dispatcher就是开始获得的/response对应的httpservlet）}}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
//这里的response和request都是/greeting那边传过来的，是同一个
```
     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//这里不是直接在页面写}}
```
}

@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.”;

}
}