Learning about Android Http request headers and response headers

2.Response header of HTTP response:

Also gives the picture in the previous section: PS: The first line is: protocol version number, status code 302 means it is not available here, but it is available in another place, and it is redirected through the Location page

HTTP Responses Header Response header information comparison table:

3. The role of the code verification response header:

Okay, after reading so many concepts, how can I do it without taking action? Right, then let's write some simple code to verify some Let’s take a look at the functions of commonly used response headers in order to deepen our understanding. Here, the server will use the simplest Servlet to implement it. If not Java Web friends only need to copy the code, configure web.xml, and add the Servlet class name, such as:

FirstServletcom.jay.server.FirstServletFirstServlet/FirstServlet

to the corresponding class name!

1) Implement page redirection through Location

Implementation code:

package com.jay.http.test;

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 ServletOne extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		//告诉浏览器响应码，以及重定向页面
		resp.setStatus(302);
		resp.setHeader("Location", "http://www.baidu.com");
	}
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		this.doGet(req, resp);
	}
}

Running result:

When we visit: http://localhost:8080/HttpTest/ServletOne, we will find that the page jumps to Baidu, Then we use FireFox’s developer tools: you can see the content of the HTTP we sent:

2) Tell the browser the compression format of the data through Content-Encoding

Implementation code:

package com.jay.http.test;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.zip.GZIPOutputStream;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletTwo extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		String data = "Fresh air and sunshine can have an amazing effect on our feelings. "
				+ "Sometimes when we are feeling down, all that we need to do is simply to go "
				+ "outside and breathe. Movement and exercise is also a fantastic way to feel better. "
				+ "Positive emotions can be generated by motion. So if we start to feel down,"
				+ " take some deep breathes, go outside, feel the fresh air, "
				+ "let the sun hit our face, go for a hike, a walk, a bike ride, "
				+ "a swim, a run, whatever. We will feel better if we do this.";
		System.out.println("原始数据长度:" + data.getBytes().length);
		// 对数据进行压缩:
		ByteArrayOutputStream bout = new ByteArrayOutputStream();
		GZIPOutputStream gout = new GZIPOutputStream(bout);
		gout.write(data.getBytes());
		gout.close();
		// 得到压缩后的数据
		byte gdata[] = bout.toByteArray();
		resp.setHeader("Content-Encoding", "gzip");
		resp.setHeader("Content-Length", gdata.length + "");
		resp.getOutputStream().write(gdata);

	}
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		doGet(req, resp);
	};
}

Running result:

gzip compressed string is not efficient for simple string compression. For example, Xiaozhu originally wrote a string of poems about a quiet night. Later, I found that the compressed size was even larger than the original one =-=...

What the server returns may sometimes be a text/html, sometimes it may be an image/jpeg, or a video/avi The browser can display the data in different ways according to the corresponding data type! Okay, here we get a

implementation code for reading PDF:

package com.jay.http.test;

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 ServletThree extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		resp.setHeader("content-type", "application/pdf");
		InputStream in = this.getServletContext().getResourceAsStream("/file/android编码规范.pdf");
		byte buffer[] = new byte[1024];
		int len = 0;
		OutputStream out = resp.getOutputStream();
		while((len = in.read(buffer)) > 0)
		{
			out.write(buffer,0,len);
		}
	}
	
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws
	   ServletException ,IOException 
	{
		doGet(req, resp);
	};
}

Running result:

HTTP Content-type comparison table

4) Use the refresh response header to let the browser jump to another page after a few seconds

Well, generally we may have such a need, such as every few seconds Refresh the page every second, or a few seconds after loading a page Jump to another page, then refresh can meet your needs~

Implementation code:

package com.jay.http.test;

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 ServletFour extends HttpServlet {
	public int second = 0;
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		//1.浏览器每隔2秒定时刷新页面
//		resp.setHeader("refresh", "2");
//		resp.getWriter().write(++second + "");
//		System.out.println("doGet方法被调用~");
		
		//2.进入页面5s后，然页跳到百度~
		resp.setHeader("refresh", "5;url='http://www.baidu.com'");
		resp.getWriter().write("HE HE DA~");
	}
	
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException ,IOException 
	{
		doGet(req, resp);
	};
}

Running result:

• 1 If the page is refreshed every 2 seconds, we can see that the displayed number is increasing, and the doGet method is also called all the time. The description page is really refreshed! If
• 2, 5 seconds after entering the page, you will jump to Baidu~

This is very simple. We only need to remove the line that sets Content-type in ③, and then add:

resp.setHeader("content-disposition", "attachment;filename=Android .pdf");

Implementation code:

package com.jay.http.test;

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 ServletFive extends HttpServlet {
	
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		resp.setHeader("content-disposition", "attachment;filename=Android.pdf");
		InputStream in = this.getServletContext().getResourceAsStream("/file/android编码规范.pdf");
		byte buffer[] = new byte[1024];
		int len = 0;
		OutputStream out = resp.getOutputStream();
		while((len = in.read(buffer)) > 0)
		{
			out.write(buffer,0,len);
		}
	}
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		doGet(req, resp);
	}
}

Running result:

This section introduces you to the request headers and response headers in Http, and also writes a few tips about adjusting the browser using response headers. some examples, I believe that after this chapter, everyone has a better understanding of the Http protocol. In the next section, we will learn about the Http provided by Android. Request method: HttpURLConnection! Okay, that’s it for this section, thank you~ By the way, download the demo of this section:

Download HttpTest.zip

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