javaweb入门（5）-- 详细了解http协议3

由于javaweb开发需要详细了解http协议中http响应的相关知识，所以，通过以下实例，对http://blog.youkuaiyun.com/java4found/article/details/8752130所描述的http响应头的作用进行深入学习。

1、用location响应头进行浏览器重定向。

     新建web工程httptest，并新建一个servlet，内容如下：

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 HttpTestServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// 302状态码与location合用，实现重定向功能
		response.setStatus(302);
		response.setHeader("location", "http://www.baidu.com");
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doGet(request, response);
	}
}

将工程部署到tomcat服务器中,访问：打开浏览器访问http://localhost:8080/httptest/Servlet/HttpTestServlet

重定向的过程：浏览器向服务器请求资源，服务器反馈数据告诉浏览器要重定向至另一个地址，浏览器向新地址发起新的请求，所在资源服务器反回用户所请求的数据。

2、用content-type响应头告诉浏览器以图片的形式打开接收到的数据。

     在项目的WebRoot新建images目录并放入一张图片。

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HttpTestServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setHeader("content-type", "image/jpeg");
		// 获取向浏览器输出数据的输出流
		OutputStream out = response.getOutputStream();

		// 读取图片文件，写入到out中
		InputStream inStream = this.getServletContext().getResourceAsStream("/images/java.jpg");
		byte[] buf = new byte[1024];
		int len = 0;
		while ((len = inStream.read(buf)) != -1) {
			out.write(buf, 0, len);
		}
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doGet(request, response);
	}
}

将工程部署到tomcat服务器中,访问：打开浏览器访问http://localhost:8080/httptest/Servlet/HttpTestServlet

可以看到浏览器将以图片的形式显示图片数据。

3、refresh响应头实现浏览器定时刷新。

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 HttpTestServlet extends HttpServlet {
	int i= 0 ;
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setHeader("Content-type", "text/html;charset=utf-8");
		
		//使用refresh响应头实现自动刷新
		response.setHeader("refresh", "3");
		//response.setHeader("refresh", "3;url=http://www.baidu.com");     //3s后刷新到百度
		
		i++;
		response.getOutputStream().write(("您第"+i+"次访问").getBytes("utf-8"));
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doGet(request, response);
	}
}

4、用content-disposition响应头来控制浏览器以下载的方式打开数据。

以第2个实例的图片为例，用content-disposition响应头告诉浏览器以下载的方式下载这张图片。

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HttpTestServlet extends HttpServlet {
	int i = 0;

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setHeader("content-disposition", "attachment;filename=java.jpg");

		InputStream inStream = this.getServletContext().getResourceAsStream(
				"/images/java.jpg");
		OutputStream out = response.getOutputStream();
		byte[] buf = new byte[1024];
		int len = 0;
		while ((len = inStream.read(buf)) != -1) {
			out.write(buf, 0, len);
		}
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doGet(request, response);
	}
}