java.net.URLConnection发送HTTP请求与通过Apache HttpClient发送HTTP请求比较

由于前段时间对java.net.URLConnection和org.apache.http.impl.client.HttpClients发送HTTP请求有所接触，发现在使用过程中碰到一些不一样的地方，特简单记录下来，以免忘记。

如果要说它们的区别，其实用过的人都知道，Java有原生的API可用于发送HTTP请求，即java.net.URL、java.net.URLConnection，这些API很好用、很常用，但不够简便；所以，才流行有许多Java HTTP请求的框架，如Apache的HttpClient。由此可见，Apache的HttpClient使用简便。

但我今天主要要说说我在使用过程中遇到的——java.net.URLConnection是请求间隔小于等于5秒，则不会新建TCP连接；如请求间隔大于5秒，则每次请求才会新建TCP连接，而Apache HttpClient在任何情况下都会新建TCP连接的问题现象及分析过程。

一.现象

为了证明这点，我特意新建了一个小工程（如下所示），向我本地的Web Application发送请求：

其中HttpRequestor.java就是从通过java.net.URLConnection发送HTTP请求中拷过来的。

ApacheClient.java

package com.bijian.study.http;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ApacheClient {

	private static final Logger logger = LoggerFactory.getLogger(ApacheClient.class);
	
	public static void httpRequest() throws Exception {
		
		CloseableHttpClient httpclient = HttpClients.createDefault();
		HttpGet httpget = new HttpGet("http://10.38.67.108:8080/SpringMVC/greeting");
		HttpResponse response = httpclient.execute(httpget);
		HttpEntity entity = response.getEntity();
		String html = EntityUtils.toString(entity);
		httpclient.close();

		logger.info(html.replaceAll("\r\n", ""));
	}
}

JavaHttpClient.java

package com.bijian.study.http;

import java.util.HashMap;
import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.bijian.study.http.urlconnection.HttpRequestor;

public class JavaHttpClient {

	private static final Logger logger = LoggerFactory.getLogger(JavaHttpClient.class);
	
	public static void httpRequest() throws Exception {
		
		/* Post Request */
		//Map<String, String> dataMap = new HashMap<String, String>();
		//dataMap.put("name", "zhangshan");
		//String html = new HttpRequestor().doPost("http://10.38.67.108:8080/SpringMVC/greeting", dataMap);
		
		/* Get Request */
		String html = new HttpRequestor().doGet("http://10.38.67.108:8080/SpringMVC/greeting?name=zhangshan");

		logger.info(html.replaceAll("\r\n", ""));
	}
}

MulThreadProcessClient.java

package com.bijian.study.client;

import com.bijian.study.http.ApacheClient;
import com.bijian.study.http.JavaHttpClient;

public class MulThreadProcessClient implements Runnable {
	
	public void run() {
		try {
			//Apache HttpClient
			//ApacheClient.httpRequest();
			
			//URLConnection HttpClient
			JavaHttpClient.httpRequest();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args) {
        
		while(true) {
			MulThreadProcessClient r = new MulThreadProcessClient();  
	        Thread t = new Thread(r);
	        t.start();
	        try {
				Thread.sleep(4000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

由于我是在Windows下进行开发的，因此采用wireshark抓包分析的，而非Linux下非常著名的tcpdump命令。

如果是ApacheClient.httpRequest()，不管每发送一次请求休眠多少时间，每次请求都会有TCP三次握手（关于具体查看TCP三次握手请参看：http://bijian1013.iteye.com/blog/2299901），即都会重新建立连接，如下所示。