JavaWeb学习-Servlet系列-24-Request请求转发和获取非表单数据

快来打我* 2022-01-31 08:29 234阅读 0赞

前面介绍Request对象获取表单数据，这篇先来介绍下请求的转发，然后介绍几个方法，是关于获取非表单数据，就是请求过程中设置属性，获取属性，删除属性这三个方法。

**1.请求转发**

准备两个ServletDemo对象，分别请求URI是/demo3和/demo4， 在Demo3中请求转发到Demo4处理。

ServletDemo3.java

package com.anthony.servlet;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    
    public class ServletDemo3 extends HttpServlet {
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		//设置编码
    		req.setCharacterEncoding("UTF-8");
    		resp.setContentType("text/html;charset=UTF-8");
    		
    		//模拟生活中办事场景
    		System.out.println("A:我要办事！");
    		System.out.println("B:这事我办不了，但我可以找人帮你办！");
    		//请求转发
    		req.getRequestDispatcher("/demo4").forward(req, resp);
    		System.out.println("B:事情办完了！");
    		
    	}
    	
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    	
    }

ServletDemo4.java

package com.anthony.servlet;
    
    import java.io.IOException;
    
    import javax.servlet.ServletException;
    import javax.servlet.ServletInputStream;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    
    public class ServletDemo4 extends HttpServlet {
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		resp.setContentType("text/html;charset=UTF-8");
    		System.out.println("C:这事我能办！");
    		
    	}
    
    
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    	
    }

测试运行下

A:我要办事！
    B:这事我办不了，但我可以找人帮你办！
    C:这事我能办！
    B:事情办完了！

浏览器就请求了/demo3地址，然后控制台输出以上信息。说起，请求转发，作为浏览器来讲只是请求了一次。自己对照代码和控制台输出顺序，思考下这个场景。

**2.获取非表单数据**

例如在Demo3中设置一个属性key1, 然后再Demo4中获取属性key1, 然后移除属性key1

package com.anthony.servlet;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    
    public class ServletDemo3 extends HttpServlet {
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		//设置编码
    		req.setCharacterEncoding("UTF-8");
    		resp.setContentType("text/html;charset=UTF-8");
    		//设置一个属性
    		String str1 = "111111";
    		req.setAttribute("key1", str1);
    		//模拟生活中办事场景
    		System.out.println("A:我要办事！");
    		System.out.println("B:这事我办不了，但我可以找人帮你办！");
    		//请求转发
    		req.getRequestDispatcher("/demo4").forward(req, resp);
    		System.out.println("B:事情办完了！");
    		
    	}
    	
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    	
    }

Demo4.java

package com.anthony.servlet;
    
    import java.io.IOException;
    
    import javax.servlet.ServletException;
    import javax.servlet.ServletInputStream;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    
    public class ServletDemo4 extends HttpServlet {
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		resp.setContentType("text/html;charset=UTF-8");
    		System.out.println("C:这事我能办！");
    		String key = (String)req.getAttribute("key1");
    		System.out.println(key);
    		//移除属性key1
    		req.removeAttribute("key1");
    		System.out.println((String)req.getAttribute("key1"));
    	}
    
    
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    	
    }

重新部署，运行结果

A:我要办事！
    B:这事我办不了，但我可以找人帮你办！
    C:这事我能办！
    111111
    null
    B:事情办完了！

**3.准发和重定向区别**

1）请求转发浏览器地址不变，重定向浏览器地址会变

2）请求转发只请求了一次，重定向请求了两次

3）请求转发能够传递数据，响应重定向不能传递数据

4）请求转发不能跳转到其他应用，例如不能跳转到百度，响应重定向可以到外部应用。