Apache HttpClient - 关闭连接

简述

如果您手动处理 HTTP 响应而不是使用响应处理程序，则需要自己关闭所有 http 连接。本章说明如何手动关闭连接。

在手动关闭 HTTP 连接时，请按照以下步骤操作 -

第 1 步 - 创建一个 HttpClient 对象

HttpClients类的createDefault()方法返回一个类的对象CloseableHttpClient，是HttpClient接口的基础实现。

使用这个方法，创建一个HttpClient对象，如下图-


CloseableHttpClient httpClient = HttpClients.createDefault();

第 2 步 - 开始一个 try-finally 块

启动一个try-finally块，在try块中编写程序中剩余的代码，在finally块中关闭CloseableHttpClient对象。


CloseableHttpClient httpClient = HttpClients.createDefault();
try{
   //Remaining code . . . . . . . . . . . . . . .
}finally{
   httpClient.close();
}

第 3 步 - 创建一个 HttpGetobject

HttpGet 类表示使用 URI 检索给定服务器信息的 HTTP GET 请求。

通过传递表示 URI 的字符串实例化 HttpGet 类来创建 HTTP GET 请求。


HttpGet httpGet = new HttpGet("http://www.cainiaoya.com/");

第 4 步 - 执行Get请求

CloseableHttpClient 对象的 execute() 方法接受 HttpUriRequest （接口）对象（即 HttpGet、HttpPost、HttpPut、HttpHead 等）并返回响应对象。

使用给定的方法执行请求 -


HttpResponse httpResponse = httpclient.execute(httpGet);

第 5 步 - 开始另一个（嵌套）try-finally

启动另一个try-finally块（嵌套在前一个try-finally中），在这个try块中编写程序中剩余的代码，并在finally块中关闭HttpResponse对象。


CloseableHttpClient httpclient = HttpClients.createDefault();
try{
   . . . . . . .
   . . . . . . .
   CloseableHttpResponse httpresponse = httpclient.execute(httpget);
   try{
      . . . . . . .
      . . . . . . .
   }finally{
      httpresponse.close();
   }
}finally{
   httpclient.close();
}

示例

每当您创建/获取对象，例如请求、响应流等时，在下一行启动一个 try finally 块，在 try 中编写剩余代码并关闭 finally 块中的相应对象，如下所示程序 -


import java.util.Scanner;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
public class CloseConnectionExample {
   
   public static void main(String args[])throws Exception{
 
      //Create an HttpClient object
      CloseableHttpClient httpclient = HttpClients.createDefault();
      try{
         //Create an HttpGet object
         HttpGet httpget = new HttpGet("http://www.cainiaoya.com/");
         //Execute the Get request
         CloseableHttpResponse httpresponse = httpclient.execute(httpget);
         try{
            Scanner sc = new Scanner(httpresponse.getEntity().getContent());
            while(sc.hasNext()) {
               System.out.println(sc.nextLine());
            }
         }finally{
            httpresponse.close();
         }
      }finally{
         httpclient.close();
      }
   }
}

输出

在执行上述程序时，会生成以下输出 -


<!DOCTYPE html>
<!--[if IE 8]><html class = "ie ie8"> <![endif]-->
<!--[if IE 9]><html class = "ie ie9"> <![endif]-->
<!--[if gt IE 9]><!-->
<html lang = "en-US"> <!--<![endif]-->
<head>
<!-- Basic -->
<meta charset = "utf-8">
<meta http-equiv = "X-UA-Compatible" content = "IE = edge">
<meta name = "viewport" content = "width = device-width,initial-scale = 1.0,userscalable = yes">
<link href = "https://cdn.muicss.com/mui-0.9.39/extra/mui-rem.min.css"
rel = "stylesheet" type = "text/css" />
<link rel = "stylesheet" href = "/questions/css/home.css?v = 3" />
<script src = "/questions/js/jquery.min.js"></script>
<script src = "/questions/js/fontawesome.js"></script>
<script src = "https://cdn.muicss.com/mui-0.9.39/js/mui.min.js"></script>
</head>
. . . . . . . . . . . . . . . . . . . . . . . . .
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<script>
window.dataLayer = window.dataLayer || [];
function gtag() {dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'UA-232293-17');
</script>
</body>
</html>