JavaWeb01_Servlet

以你之姓@ 2022-12-08 04:16 184阅读 0赞

**JavaWeb01\_Servlet**

--------------------

**入门项目：**

创建Maven项目，选择webapp模板。

**依赖：**

<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>

**在webapp目录下创建header.html：**

<!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>

**启动**

请求 **http://localhost:8080/javawebdemo**，访问的是webapp目录下默认创建的 **index.jsp**  
请求 **http://localhost:8080/javawebdemo/header.html** 可访问到我们创建的 **header.html**  
请求 **http://localhost:8080/javawebdemo/hello** 可访问到我们编写的Servlet

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JMVV8xMTE_size_16_color_FFFFFF_t_70_pic_left]

**Servlet**

Servlet是sun公司开发动态web的一门技术，它是一个接口  
如果你想开发一个Servlet程序，只需以下两步：

*  编写一个类，实现 Servlet 接口
 *  将开发好的 java 类部署到web服务器中

![在这里插入图片描述][20200917154817276.png_pic_left]

**ServletContext**

**ServletContext** 对象代表当前的Web应用，可用于 Servlet 间的数据共享通信

*  **AServlet：** 在 **ServletContext** 中设置值

@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：** 从 **ServletContext** 中取值

@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);
    }

注意：需要先请求**AServlet**给username赋值，然后请求**BServlet**才能获得值，否则值为空。

--------------------

**ServletContext** 的应用——**设置web初始化参数：**

<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);
    }

**ServletContext** 的应用——**实现请求转发（路径不变）：**

*  **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");	
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JMVV8xMTE_size_16_color_FFFFFF_t_70_pic_left 1]  
**ServletContext** 的应用——**读取资源：**

*  **在src/main/resources目录下创建db.properties文件：**

username=root
    password=123456

*  **在Servlet中读取配置文件**

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    	//InputStream is = this.getClass().getClassLoader().getResourceAsStream("db.properties");
    	InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
    	Properties prop = new Properties();
    	prop.load (is);
    	String username = prop.getProperty("username");
    	String password = prop.getProperty("password");
    	System.out.println(username);
    	System.out.println(password);	
    }

--------------------

**servletConfig**

<servlet>
    	<servlet-name>AServlet</servlet-name>
    	<servlet-class>com.blu.servlet.AServlet</servlet-class>
    	<init-param>
    		<param-name>ip</param-name>
    		<param-value>127.0.0.1</param-value>
    	</init-param>
    </servlet>
    <servlet-mapping>
    	<servlet-name>AServlet</servlet-name>
    	<url-pattern>/a</url-pattern>
    </servlet-mapping>

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
    	System.out.println("进入AServlet");
    	ServletConfig servletConfig = this.getServletConfig();
    	System.out.println(servletConfig.getInitParameter("ip"));
    }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JMVV8xMTE_size_16_color_FFFFFF_t_70_pic_left]: /images/20221123/adbe168d08e245c1bc23f91ec7842bef.png
[20200917154817276.png_pic_left]: /images/20221123/6b6d38b8091b488fa7c32f91e7f8a119.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0JMVV8xMTE_size_16_color_FFFFFF_t_70_pic_left 1]: /images/20221123/f02fde33e54c4757bf08e49cfde40426.png