如果请求里有这个range头，那么响应里也有

1.首先在webroot下放好a.txt

内容如下：

2.然后在本地有个下载未完成的a.txt

本地a.txt内容如下：

DEMO：创建class

url：对应着eclipes里的a.txt

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new FileOutputStream("/Users/snowing/Documents/a.txt",true);----》代表下载未完成的a.txt
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package cn.itcaste.web.servlet;
 
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
 
public class RangeDemo {
    public static void main(String[] args) throws Exception {
        URL url=new URL("http://localhost:8082/day04/a.txt");
    HttpURLConnection httpurlconnection=(HttpURLConnection) url.openConnection();
    httpurlconnection.setRequestProperty("Range", "bytes=5-");
     InputStream in=httpurlconnection.getInputStream();
     int len=0;
     byte buffer[]=new byte[1024];
     FileOutputStream out =new FileOutputStream("/Users/snowing/Documents/a.txt",true);//true:代表接着aaaaa继续下载而不是删除aaaaa再下载
     while((len=in.read(buffer))>0){
          out.write(buffer, 0, len);
     }
     in.close();
     out.close(); 
    }
 
}

　　结果：

1.http相应格式

状态码：HTTP／1.1 OK

状态码

2.http状态行

200--》ok

302--》找别人要资源

304/307--》我不给你，你去缓存拿吧

403--》没权限

404-》地址错了，或者没资源

505-》服务器端问题

3.响应头

3.1.1location：这个头配合302使用，用于告诉客户找谁

用302和location进行重定向

创建servlet进行尝试

package cn.itcaste.web.servlet;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

 * Servlet implementation class servelt

 */

@WebServlet("/servelt")

public class servelt extends HttpServlet {

	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//		response.getWriter().append("Served at: ").append(request.getContextPath());

		response.setStatus(302);

		response.setHeader("location","/day04/WebContent/1.html");

	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		doGet(request, response);

	}

}

3.1.2 servlet压缩传输数据

response.setHeader("Content-Encoding","gzip");

Content-Encoding--->通过这个头，浏览器知道数据压缩格式

response.setHeader("Content-Length", gzip.length+"");

Content-Length--->通过这个头，浏览器知道回送数据长度

package cn.itcaste.web.servlet;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.util.zip.GZIPOutputStream;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

 * Servlet implementation class servelt

 */

@WebServlet("/servelt")

public class servelt extends HttpServlet {

	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//		response.getWriter().append("Served at: ").append(request.getContextPath());

		String data ="aaaaaaqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq";

		System.out.println("原始数据大小：" + data.getBytes().length);

		ByteArrayOutputStream bout=new ByteArrayOutputStream();//缓冲流 底层流

		GZIPOutputStream gout= new GZIPOutputStream(bout);//使用缓冲区大小创建新的输出流（包装流）

		gout.write(data.getBytes());//将字符数组写入压缩流

		gout.close();//数据小的时候输出流关闭才能写进去，或者写满

		byte gzip[] = bout.toByteArray();//得到压缩后的数据，写到了缓冲流里去了

		System.out.println("压缩后大小"+gzip.length);

		response.getOutputStream().write(gzip);//压缩数据打给浏览器

		//通知浏览器数据采用压缩格式

		response.setHeader("Content-Encoding","gzip");

		response.setHeader("Content-Length", gzip.length+"");

		response.getOutputStream().write(gzip);

	}

控制台：

原始数据大小：85

压缩后大小26

3.1.3 content-type--->通过这个头，浏览器知道回送数据格式

Tomcat 里的文件web.xml配置市面上常见的数据格式，不知道可以去这里找 距离：

</mime-mapping>

    <mime-mapping>

        <extension>jnlp</extension>

        <mime-type>application/x-java-jnlp-file</mime-type>

    </mime-mapping>

    <mime-mapping>

        <extension>joda</extension>

        <mime-type>application/vnd.joost.joda-archive</mime-type>

    </mime-mapping>

3.1.4 Last-Modified--->通过这个头，告诉浏览器当前资源缓存时间

3.1.5 Refresh:通过这个头告诉浏览器隔多长时间刷新一次

		response.setHeader("Refresh", "3；url='http://www.sina.com'");//隔三秒刷新一下资源,跳到新浪官网

		//response.setHeader("Refresh", "3；url='http://www.sina.com'");//每隔三秒刷新一下资源，适用于股票页面，聊天页面

		String data= "aaaaa";

		response.getOutputStream().write(data.getBytes());

3.1.6Content-Disposition--->通过这个头，告诉浏览器下载方式打开数据

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		response.setHeader("content-disposition", "attachment;filename=3.jpg");//通过这个头，告诉浏览器下载方式打开数据

		InputStream in=this.getServletContext().getResourceAsStream("/1.jpg");//通过这个头，浏览器知道回送数据格式

		int len=0;

		byte buffer[] = new byte[1024];

		OutputStream out=response.getOutputStream();

		while((len=in.read(buffer))>0){

			out.write(buffer,0,len );

			}

	}

　　下载方式打开

整个DEMO

package cn.itcaste.web.servlet;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.util.zip.GZIPOutputStream;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

 * Servlet implementation class servelt

 */

@WebServlet("/servlet")

public class servlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//		response.getWriter().append("Served at: ").append(request.getContextPath());	

	}

	private void test5(HttpServletResponse response) throws IOException {

		response.setHeader("content-disposition", "attachment;filename=3.jpg");//通过这个头，告诉浏览器下载方式打开数据

		InputStream in=this.getServletContext().getResourceAsStream("/1.jpg");//通过这个头，浏览器知道回送数据格式

		int len=0;

		byte buffer[] = new byte[1024];

		OutputStream out=response.getOutputStream();

		while((len=in.read(buffer))>0){

			out.write(buffer,0,len );

			}

	}

//刷新数据

	private void test4(HttpServletResponse response) throws IOException {

		response.setHeader("Refresh", "3；url='http://www.sina.com'");//隔三秒刷新一下资源,跳到新浪官网

		//response.setHeader("Refresh", "3；url='http://www.sina.com'");//每隔三秒刷新一下资源，适用于股票页面，聊天页面

		String data= "aaaaa";

		response.getOutputStream().write(data.getBytes());

	}

//解析不同类型的数据

	private void test3(HttpServletResponse response) throws IOException {

	response.setHeader("content-type", "image/jpeg");//格式去web.xml里找

	InputStream in=this.getServletContext().getResourceAsStream("/1.jpg");//通过这个头，浏览器知道回送数据格式

	int len=0;

	byte buffer[] = new byte[1024];

	OutputStream out=response.getOutputStream();

	while((len=in.read(buffer))>0){

		out.write(buffer,0,len );

		}

		}

	private void test2(HttpServletResponse response) throws IOException {

		String data ="aaaaaaqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq";

		System.out.println("原始数据大小：" + data.getBytes().length);

		ByteArrayOutputStream bout=new ByteArrayOutputStream();//缓冲流 底层流

		GZIPOutputStream gout= new GZIPOutputStream(bout);//使用缓冲区大小创建新的输出流（包装流）

		gout.write(data.getBytes());//将字符数组写入压缩流

		gout.close();//数据小的时候输出流关闭才能写进去，或者写满

		byte gzip[] = bout.toByteArray();//得到压缩后的数据，写到了缓冲流里去了

		System.out.println("压缩后大小"+gzip.length);

		response.getOutputStream().write(gzip);//压缩数据打给浏览器

		//通知浏览器数据采用压缩格式

		response.setHeader("Content-Encoding","gzip");

		response.setHeader("Content-Length", gzip.length+"");

		response.getOutputStream().write(gzip);

	}

	//用302和location进行重定向

	public void test1(HttpServletResponse response){

		response.setStatus(302);

		response.setHeader("location","/day04/WebContent/1.html");

	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		doGet(request, response);

	}

}

　　

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