使用httpclient4心得

最近项目中使用httpclient4,发现总是存在http请求未关闭情况，因此找了官网的demo记录一下。

package org.apache.http.examples.client;

import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

public class QuickStart {

    public static void main(String[] args) throws Exception {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpGet httpGet = new HttpGet("http://targethost/homepage");
            CloseableHttpResponse response1 = httpclient.execute(httpGet);
            // The underlying HTTP connection is still held by the response object
            // to allow the response content to be streamed directly from the network socket.
            // In order to ensure correct deallocation of system resources
            // the user MUST call CloseableHttpResponse#close() from a finally clause.
            // Please note that if response content is not fully consumed the underlying
            // connection cannot be safely re-used and will be shut down and discarded
            // by the connection manager.
            try {
                System.out.println(response1.getStatusLine());
                HttpEntity entity1 = response1.getEntity();
                // do something useful with the response body
                // and ensure it is fully consumed
                EntityUtils.consume(entity1);
            } finally {
                response1.close();
            }

            HttpPost httpPost = new HttpPost("http://targethost/login");
            List <NameValuePair> nvps = new ArrayList <NameValuePair>();
            nvps.add(new BasicNameValuePair("username", "vip"));
            nvps.add(new BasicNameValuePair("password", "secret"));
            httpPost.setEntity(new UrlEncodedFormEntity(nvps));
            CloseableHttpResponse response2 = httpclient.execute(httpPost);

            try {
                System.out.println(response2.getStatusLine());
                HttpEntity entity2 = response2.getEntity();
                // do something useful with the response body
                // and ensure it is fully consumed
                EntityUtils.consume(entity2);
            } finally {
                response2.close();
            }
        } finally {
            httpclient.close();
        }
    }

}

提示一说明：

1.HTTP连接隐藏在response对象中，以便于response流在网络中传递。

2.为了保证系统资源的重新分配，必须使用CloseableHttpResponse#close()关闭连接

3.请注意如果response内容没有被毁灭掉，http连接将不能被安全地再次使用，可能被连接管理器关闭掉或丢弃掉。

提示二说明

返回responseBody的方法

// 获取内容
String responseBody = EntityUtils.toString(response.getEntity());

二、常见问题

在使用的过程中抛出如下错误

 java.lang.IllegalArgumentException: Entity may not be null
    at org.apache.http.util.Args.notNull(Args.java:48)
    at org.apache.http.util.EntityUtils.toString(EntityUtils.java:213)
    at org.apache.http.util.EntityUtils.toString(EntityUtils.java:288)

经排查代码使用

 EntityUtils.toString(response.getEntity());

当304响应时，entity为NULL，因此抛出异常。