在HttpClient API中获取状态代码的快速指南。 getStatusLine（）。getStatusCode（）示例和相关的错误。

1.简介

在这个非常快速的教程中，我将展示如何使用HttpClient 4获取和验证HTTP响应的StatusCode。

2. Maven依赖

要运行此HttiClient应用程序，需要以下jar。

commons-logging在内部被其他jar使用。 请不要忘记添加这些jar，否则会出现编译时和运行时错误。

<dependency><groupId>commons-logging</groupId><artifactId>commons-logging</artifactId><version>1.2</version>
</dependency><dependency><groupId>org.apache.httpcomponents</groupId><artifactId>httpclient</artifactId><version>4.5.12</version>
</dependency><dependency><groupId>org.apache.httpcomponents</groupId><artifactId>httpcore</artifactId><version>4.4.13</version>
</dependency>

错误：

如果您错过了commons-logging jar，则会产生以下异常。

 Exception in thread "main" Exception in thread java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory at org.apache.http.conn.ssl.DefaultHostnameVerifier.<init>(DefaultHostnameVerifier.java: 82 ) at org.apache.http.impl.client.HttpClientBuilder.build(HttpClientBuilder.java: 966 ) at com.java.w3schools.blog.HttpClient.HttpClientGetStatusCode.main(HttpClientGetStatusCode.java: 21 )  Caused by: java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java: 583 ) at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java: 178 ) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java: 521 ) ... 3 more 

3.从Http响应中检索状态代码

发送HTTP请求后，经过处理后，响应将发送回调用方。

 package com.java.w3schools.blog.HttpClient;  import java.io.IOException;  import org.apache.http.HttpStatus;  import org.apache.http.client.ClientProtocolException;  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.HttpClientBuilder;  public class HttpClientGetStatusCode { private static final String GOOGLE_URL = " http://www.google.com " ; private static CloseableHttpClient instance; private static CloseableHttpResponse response; public static void main(String[] args) throws ClientProtocolException, IOException { HttpGet httpGet = new HttpGet(GOOGLE_URL); instance = HttpClientBuilder.create().build(); response = instance.execute(httpGet); System.out.println( "response.getStatusLine() :: " + response.getStatusLine()); final int statusCode = response.getStatusLine().getStatusCode(); int code = HttpStatus.SC_OK; if (code == statusCode) { System.out.println( "Status Code : " + code); } else { System.out.println( "StatusCode not 200 : " + code); } }  } 

返回的响应类型为org.apache.http.HttpResponse ，它使我们能够获取请求的执行状态。 getStatusLine（）方法返回保存请求状态的StatusLine对象。 采用
getStatusCode（）仅获取执行代码。

输出：

 response.getStatusLine() :: HTTP/ 1.1 200 OK  Status Code : 200 

4. URL断开时例外

如果给定的URL关闭或错误，则我们将获得UnknownHostException运行时异常。

 Exception in thread "main" Exception in thread java.net.UnknownHostException: www.google.com1: nodename nor servname provided, or not known at java.base/java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method) at java.base/java.net.InetAddress$PlatformNameService.lookupAllHostAddr(InetAddress.java: 929 ) at java.base/java.net.InetAddress.getAddressesFromNameService(InetAddress.java: 1515 ) at java.base/java.net.InetAddress$NameServiceAddresses.get(InetAddress.java: 848 ) at java.base/java.net.InetAddress.getAllByName0(InetAddress.java: 1505 ) at java.base/java.net.InetAddress.getAllByName(InetAddress.java: 1364 ) at java.base/java.net.InetAddress.getAllByName(InetAddress.java: 1298 ) at org.apache.http.impl.conn.SystemDefaultDnsResolver.resolve(SystemDefaultDnsResolver.java: 45 ) at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java: 112 ) at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java: 376 ) at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java: 393 ) at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java: 236 ) at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java: 186 ) at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java: 89 ) at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java: 110 ) at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java: 185 ) at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java: 83 ) at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java: 108 ) at com.java.w3schools.blog.HttpClient.HttpClientGetStatusCode.main(HttpClientGetStatusCode.java: 24 ) 

5.结论

在本文中，我们已经看到了如何获取HttpClient请求的状态代码 。

和往常一样，本文显示的示例在Github上。

GitHub代码

翻译自: https://www.javacodegeeks.com/2020/04/httpclient-4-api-get-the-status-code-getstatusline-getstatuscode-example.html