Apache HttpClient GET HTTP请求示例

转x33g5p2x  于2022-10-07 转载在 Apache  
字(8.0k)|赞(0)|评价(0)|浏览(937)

在这篇快速文章中，我们将逐步讨论如何使用Apache HttpClient 4.5来进行Http GET请求。HTTP GET方法表示指定资源的代表。这可以是简单的获得一个HTML页面，或获得JSON、XML或等格式的资源。使用HTTP GET请求方法的请求应该是Idempotent的，也就是说：这些请求应该只检索数据，不应该有其他效果。
HttpClient支持HTTP/1.1规范中定义的所有HTTP方法：GET、HEAD、POST、PUT、DELETE、TRACE和OPTIONS。每个方法类型都有一个特定的类：HttpGet、HttpHead、HttpPost、HttpPut、HttpDelete、HttpTrace和HttpOptions。

在这个例子中，我们将使用HttpGet类来处理GET HTTP方法。查看Apache HttpClient POST HTTP请求实例

使用Apache HttpClient - 添加依赖

Apache HttpClient库允许处理HTTP请求。要使用这个库，请在你的Maven或Gradle构建文件中添加一个依赖项。你可以在这里找到最新版本：https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient

我们使用maven来管理我们的依赖，并使用Apache HttpClient 4.5版。在你的项目中添加以下依赖，以便进行HTTP POST请求方式。

  1. <dependency>
  2.  <groupId>org.apache.httpcomponents</groupId>
  3.  <artifactId>httpclient</artifactId>
  4.  <version>4.5</version>
  5. </dependency>

开发步骤

让我们创建一个逐步的例子，使用HttpClient做一个HTTP GET请求。

1. 使用辅助类HttpClients创建CloseableHttpClient的实例。

  1. CloseableHttpClient httpclient = HttpClients.createDefault()

HttpClients.createDefault()方法以默认配置创建CloseableHttpClient实例。

2. 创建一个基本的GET请求

  1. HttpGet httpget = new HttpGet("http://httpbin.org/get");

3. 创建一个自定义的响应处理程序

  1. ResponseHandler < String > responseHandler = response - > {
  2.     int status = response.getStatusLine().getStatusCode();
  3.     if (status >= 200 && status < 300) {
  4.         HttpEntity entity = response.getEntity();
  5.         return entity != null ? EntityUtils.toString(entity) : null;
  6.     } else {
  7.         throw new ClientProtocolException("Unexpected response status: " + status);
  8.     }
  9. };

4. 通过execute()方法发送基本的GET请求

  1. String responseBody = httpclient.execute(httpget, responseHandler);

5. 获取HTTP响应的状态代码

  1. int status = response.getStatusLine().getStatusCode();

6. 获取一个响应实体

  1. HttpEntity entity = response.getEntity();

HttpClient HTTP GET请求方法实例

在下面的例子中，我们从http://httpbin.org/get检索一个资源。这个资源返回一个JSON对象，我们将简单地打印到控制台。在这个例子中，我们使用Java 7 try-with-resources来自动处理ClosableHttpClient的关闭，我们也使用Java 8 lambdas来处理ResponseHandler。

  1. package com.javadevelopersguide.httpclient.examples;
  3. import org.apache.http.HttpEntity;
  5. import org.apache.http.client.ClientProtocolException;
  6. import org.apache.http.client.ResponseHandler;
  7. import org.apache.http.client.methods.HttpGet;
  8. import org.apache.http.impl.client.CloseableHttpClient;
  9. import org.apache.http.impl.client.HttpClients;
  10. import org.apache.http.util.EntityUtils;
  11. import java.io.IOException;
  13. /**
  14. * This example demonstrates the use of {@link HttpGet} request method.
  15. * @author Ramesh Fadatare
  16. */
  17. public class HttpGetRequestMethodExample {
  19.     public static void main(String...args) throws IOException {
  20.         try (CloseableHttpClient httpclient = HttpClients.createDefault()) {
  22.             //HTTP GET method
  23.             HttpGet httpget = new HttpGet("http://httpbin.org/get");
  24.             System.out.println("Executing request " + httpget.getRequestLine());
  26.             // Create a custom response handler
  27.             ResponseHandler < String > responseHandler = response - > {
  28.                 int status = response.getStatusLine().getStatusCode();
  29.                 if (status >= 200 && status < 300) {
  30.                     HttpEntity entity = response.getEntity();
  31.                     return entity != null ? EntityUtils.toString(entity) : null;
  32.                 } else {
  33.                     throw new ClientProtocolException("Unexpected response status: " + status);
  34.                 }
  35.             };
  36.             String responseBody = httpclient.execute(httpget, responseHandler);
  37.             System.out.println("----------------------------------------");
  38.             System.out.println(responseBody);
  39.         }
  40.     }
  41. }

输出：

  1. Executing request GET http://httpbin.org/get HTTP/1.1
  2. ----------------------------------------
  3. {
  4.   "args": {}, 
  5.   "headers": {
  6.     "Accept-Encoding": "gzip,deflate", 
  7.     "Connection": "close", 
  8.     "Host": "httpbin.org", 
  9.     "User-Agent": "Apache-HttpClient/4.5 (Java/1.8.0_172)"
  10.   }, 
  11.   "origin": "49.35.12.218", 
  12.   "url": "http://httpbin.org/get"
  13. }

更多的例子

让我们来讨论如何在实时项目中使用HttpClient。考虑到我们已经部署了Spring boot Restful CRUD APIs。请看这篇文章 - Spring Boot 2 + hibernate 5 + CRUD REST API教程。

让我们写一个Rest客户端，从以下Rest服务中获取JSON

  1. package com.javadevelopersguide.httpclient.examples;
  3. import java.io.IOException;
  5. import org.apache.http.HttpEntity;
  6. import org.apache.http.client.ClientProtocolException;
  7. import org.apache.http.client.ResponseHandler;
  8. import org.apache.http.client.methods.HttpGet;
  9. import org.apache.http.impl.client.CloseableHttpClient;
  10. import org.apache.http.impl.client.HttpClients;
  11. import org.apache.http.util.EntityUtils;
  13. /**
  14. * This example demonstrates the use of {@link HttpGet} request method.
  15. * @author Ramesh Fadatare
  16. */
  17. public class HttpGetRequestMethodExample {
  19.     public static void main(String[] args) throws IOException {
  20.         getUsers();
  21.         getUserById();
  22.     }
  24.     private static void getUsers() throws ClientProtocolException, IOException {
  25.         try (CloseableHttpClient httpclient = HttpClients.createDefault()) {
  27.             //HTTP GET method
  28.             HttpGet httpget = new HttpGet("http://localhost:8080/api/v1/users");
  29.             System.out.println("Executing request " + httpget.getRequestLine());
  31.             // Create a custom response handler
  32.             ResponseHandler < String > responseHandler = response - > {
  33.                 int status = response.getStatusLine().getStatusCode();
  34.                 if (status >= 200 && status < 300) {
  35.                     HttpEntity entity = response.getEntity();
  36.                     return entity != null ? EntityUtils.toString(entity) : null;
  37.                 } else {
  38.                     throw new ClientProtocolException("Unexpected response status: " + status);
  39.                 }
  40.             };
  41.             String responseBody = httpclient.execute(httpget, responseHandler);
  42.             System.out.println("----------------------------------------");
  43.             System.out.println(responseBody);
  44.         }
  45.     }
  47.     private static void getUserById() throws IOException {
  48.         try (CloseableHttpClient httpclient = HttpClients.createDefault()) {
  50.             //HTTP GET method
  51.             HttpGet httpget = new HttpGet("http://localhost:8080/api/v1/users/5");
  52.             System.out.println("Executing request " + httpget.getRequestLine());
  54.             // Create a custom response handler
  55.             ResponseHandler < String > responseHandler = response - > {
  56.                 int status = response.getStatusLine().getStatusCode();
  57.                 if (status >= 200 && status < 300) {
  58.                     HttpEntity entity = response.getEntity();
  59.                     return entity != null ? EntityUtils.toString(entity) : null;
  60.                 } else {
  61.                     throw new ClientProtocolException("Unexpected response status: " + status);
  62.                 }
  63.             };
  64.             String responseBody = httpclient.execute(httpget, responseHandler);
  65.             System.out.println("----------------------------------------");
  66.             System.out.println(responseBody);
  67.         }
  68.     }
  69. }

输出

  1. Executing request GET http://localhost:8080/api/v1/users HTTP/1.1
  2. ----------------------------------------
  3. [{"id":5,"firstName":"Ram","lastName":"Jadhav","emailId":"ramesh123@gmail.com","createdAt":"2018-09-11T11:19:56.000+0000",
  4. "createdBy":"Ramesh","updatedAt":"2018-09-11T11:26:31.000+0000","updatedby":"Ramesh"},
  5. {"id":6,"firstName":"Ramesh","lastName":"fadatare","emailId":"ramesh@gmail.com","createdAt":"2018-09-11T11:20:07.000+0000",
  6. "createdBy":"Ramesh","updatedAt":"2018-09-11T11:20:07.000+0000","updatedby":"Ramesh"},
  7. {"id":17,"firstName":"John","lastName":"Cena","emailId":"john@gmail.com","createdAt":"2018-09-19T08:28:10.000+0000",
  8. "createdBy":"Ramesh","updatedAt":"2018-09-19T08:28:10.000+0000","updatedby":"Ramesh"},
  9. {"id":18,"firstName":"John","lastName":"Cena","emailId":"john@gmail.com","createdAt":"2018-09-19T08:29:29.000+0000",
  10. "createdBy":"Ramesh","updatedAt":"2018-09-19T08:29:29.000+0000","updatedby":"Ramesh"}]
  11. Executing request GET http://localhost:8080/api/v1/users/5 HTTP/1.1
  12. ----------------------------------------
  13. {"id":5,"firstName":"Ram","lastName":"Jadhav","emailId":"ramesh123@gmail.com","createdAt":"2018-09-11T11:19:56.000+0000",
  14. "createdBy":"Ramesh","updatedAt":"2018-09-11T11:26:31.000+0000","updatedby":"Ramesh"}

版权说明 : 本文为转载文章, 版权归原作者所有 版权申明

原文链接 : https://www.javaguides.net/2018/10/apache-httpclient-get-http-request-example.html

内容来源于网络，如有侵权，请联系作者删除！

相关文章

    查看更多

    热门标签

    更多
    JavaquerypythonNode开发语言requestUtil数据库Table后端算法LoggerMessageElementParser

    最新文章

    更多
    • 蜀ICP备13028337号-1 大数据知识库 https://www.saoniuhuo.com © All rights reserved
    • 本站内容来源互联网,如果侵犯您的权益请联系我们删除, 联系方式：448109455@qq.com