JavaWeb01_Servlet

JavaWeb01_Servlet

Entry project:

Create a Maven project and select the webapp template.

rely:

<dependencies>
	<dependency>
		<groupId>javax.servlet</groupId>
		<artifactId>javax.servlet-api</artifactId>
		<version>4.0.1</version>
	</dependency>
	<dependency>
		<groupId>junit</groupId>
		<artifactId>junit</artifactId>
		<version>3.8.1</version>
		<scope>test</scope>
	</dependency>
</dependencies>

package com.blu.servlet;

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;

public class HelloServlet extends HttpServlet {
    
    

	@Override
	public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
    
    
		response.setContentType("text/html");
		//java默认的字符编码是ISO-8859-1，中文会乱码！
		response.setCharacterEncoding("utf-8");
		
		PrintWriter out = response.getWriter();
		out.println("<html>");
		out.println("<head>");
		out.println("<title>Hello BLU!</title>");
		out.println("</head>");
		out.println("<body>");
		out.println("<h1>你好 BLU!</h1>");
		out.println("</body>");
		out.println("</html>");
	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
		super.doPost(req, resp);
	}

}

web.xml ：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                         http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">
  
  <servlet>
  	<servlet-name>helloServlet</servlet-name>
  	<servlet-class>com.blu.servlet.HelloServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>helloServlet</servlet-name>
  	<url-pattern>/hello</url-pattern>
  </servlet-mapping>
  
</web-app>

Create header.html in the webapp directory:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>标题1</h1>
<p>Hi,BLU!</p>
</body>
</html>

start up

Request http://localhost:8080/javawebdemo , visit the index.jsp created by default in the webapp directory.
Request http://localhost:8080/javawebdemo/header.html to access the header.html we created.
Request http:/ /localhost:8080/javawebdemo/hello can access the Servlet we wrote

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Servlet

Servlet is a technology used by Sun to develop dynamic web. It is an interface.
If you want to develop a Servlet program, you only need the following two steps:

Write a class to implement the Servlet interface
Deploy the developed java classes to the web server

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ServletContext

The ServletContext object represents the current Web application and can be used for data sharing and communication between Servlets

AServlet: Set the value in ServletContext

@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
    
    
	
	response.setContentType("text/html");
	response.setCharacterEncoding("utf-8");
	ServletContext servletContext = this.getServletContext();
	servletContext.setAttribute("username", "BLU");
		
}

BServlet: take value from ServletContext

@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
		
	resp.setContentType("text/html");
	resp.setCharacterEncoding("utf-8");
	
	ServletContext servletContext = this.getServletContext();
	String username = (String) servletContext.getAttribute("username");
	resp.getWriter().print("名字："+username);
}

Note: You need to request AServlet to assign a value to username, and then request BServlet to get the value, otherwise the value is empty.

ServletContext application- set web initialization parameters:

<context-param>
	<param-name>url</param-name>
	<param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
</context-param>

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
	ServletContext servletContext = this.getServletContext();
	String url = servletContext.getInitParameter("url");
	System.out.println(url);
}

Application of ServletContext -to achieve request forwarding:

AServlet ：

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
	System.out.println("进入AServlet");
	ServletContext servletContext = this.getServletContext();
	RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/b");
	requestDispatcher.forward(req, resp);
}

BServlet ：

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
	System.out.println("进入BServlet");
	resp.setContentType("text/html");
	resp.setCharacterEncoding("utf-8");
	PrintWriter out = resp.getWriter();
	out.println("Welcome to BServlet");	
}

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