引言： 在现代的网络应用程序中，进行HTTP请求是一项常见的任务。Apache HttpClient是一个功能强大且广泛使用的Java库，它提供了方便的方法来执行HTTP请求并处理响应。本文将介绍如何使用HttpClient库进行HTTP请求，包括GET请求、POST请求、添加参数和请求体、设置请求头等操作。

HttpClient简介： HttpClient是一个开源的Java库，用于处理HTTP通信。它提供了各种类和方法，使得执行HTTP请求变得简单而直观。HttpClient不仅支持基本的HTTP协议功能，还提供了更高级的功能，如连接管理、cookie管理、代理设置等。

导入HttpClient库

在使用HttpClient之前，需要在项目中导入HttpClient库。可以通过在Maven项目的pom.xml文件中添加以下依赖项来实现：

xml复制代码<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
</dependency>

发起GET请求

GET请求是获取服务器资源的一种常见方式。下面是使用HttpClient进行GET请求的示例代码：

ini复制代码HttpGet httpGet = new HttpGet("http://httpbin.org/get");
CloseableHttpResponse response = client.execute(httpGet);
System.out.println(EntityUtils.toString(response.getEntity()));

在上述代码中，我们创建了一个HttpGet对象，并传入要请求的URL。然后使用HttpClient的execute方法发送请求并获取响应。最后，通过EntityUtils将响应内容转换为字符串并进行输出。

发起POST请求

POST请求用于向服务器提交数据。下面是使用HttpClient进行POST请求的示例代码：

ini复制代码HttpPost httpPost = new HttpPost("http://httpbin.org/post");
CloseableHttpResponse response = client.execute(httpPost);
System.out.println(EntityUtils.toString(response.getEntity()));

与GET请求相比，POST请求的代码几乎相同。只需将HttpGet替换为HttpPost即可。

添加请求参数

有时候我们需要在请求中添加参数。使用HttpClient的URIBuilder类可以方便地构建带有参数的URL。下面是一个示例：

ini复制代码URIBuilder builder = new URIBuilder("http://httpbin.org/post");
builder.addParameter("name", "Ru");
builder.addParameter("age", "18");
URI uri = builder.build();
HttpPost httpPost = new HttpPost(uri);
CloseableHttpResponse response = client.execute(httpPost);
System.out.println(EntityUtils.toString(response.getEntity()));

在上述代码中，我们创建了一个URIBuilder对象，并使用addParameter方法添加了两个参数。然后通过build方法生成最终的URI，将其传递给HttpPost对象进行请求。

设置请求体

有时候我们需要在POST请求中添加请求体，通常使用JSON格式进行数据传输。下面是一个示例：

ini复制代码HttpPost httpPost = new HttpPost("http://httpbin.org/post");  
String jsonBody = "{"name": "Ru", "age": 18}";  
// 设置请求头部信息  
httpPost.setHeader("Content-Type", "application/json");  
  
// 设置请求体  
StringEntity requestEntity = new StringEntity(jsonBody, ContentType.APPLICATION_JSON);  
httpPost.setEntity(requestEntity);  
CloseableHttpResponse response = client.execute(httpPost);  
HttpEntity responseEntity = response.getEntity();  
if (responseEntity != null) {  
    String responseBody = EntityUtils.toString(responseEntity);  
    System.out.println(responseBody);  
}

在上述代码中，我们首先设置了请求的Content-Type为application/json，然后创建了一个StringEntity对象来封装请求体数据。将其设置为HttpPost对象的实体，并执行请求。最后，通过EntityUtils将响应体转换为字符串并进行输出。

设置请求头

有时候我们需要在请求中添加自定义的请求头信息，如User-Agent、Authorization等。下面是一个示例：

vbscript复制代码HttpGet httpGet = new HttpGet("http://httpbin.org/get");
httpGet.setHeader("User-Agent", "MyHttpClient/1.0");
httpGet.setHeader("Authorization", "Bearer my_token");
CloseableHttpResponse response = client.execute(httpGet);
System.out.println(EntityUtils.toString(response.getEntity()));

在上述代码中，我们使用setHeader方法设置了两个自定义的请求头信息，然后执行GET请求并输出响应结果。

完整demo：

java复制代码package org.example.TestMaven;

import org.apache.http.HttpEntity;
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.client.utils.URIBuilder;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class HttpClientDemo {
    static CloseableHttpClient client = HttpClients.createDefault();

    public static void main(String[] args) throws IOException, URISyntaxException {

//        httpGetDemo();
//        httpPostDemo();
//        httpParamsDemo();
//        httpBodyDemo();
        httpHeaderDemo();
    }
    public static void httpGetDemo() throws IOException {
        HttpGet httpGet = new HttpGet("http://httpbin.org/get");
        CloseableHttpResponse response = client.execute(httpGet);
        System.out.println(EntityUtils.toString(response.getEntity()));
    }

    public static void httpPostDemo() throws IOException {
        HttpPost httpPost = new HttpPost("http://httpbin.org/post");
        CloseableHttpResponse response = client.execute(httpPost);
        System.out.println(EntityUtils.toString(response.getEntity()));
    }

    public static void httpParamsDemo() throws IOException, URISyntaxException {
        URIBuilder builder = new URIBuilder("http://httpbin.org/post");
        builder.addParameter("name", "Ru");
        builder.addParameter("age", "18");
        URI uri = builder.build();
        HttpPost httpPost = new HttpPost(uri);
        CloseableHttpResponse response = client.execute(httpPost);
        System.out.println(EntityUtils.toString(response.getEntity()));
    }

    public static void httpBodyDemo() throws IOException {
        HttpPost httpPost = new HttpPost("http://httpbin.org/post");
        String jsonBody = "{"name": "Ru", "age": 18}";
        // 设置请求头部信息
        httpPost.setHeader("Content-Type", "application/json");

        // 设置请求体
        StringEntity requestEntity = new StringEntity(jsonBody, ContentType.APPLICATION_JSON);
        httpPost.setEntity(requestEntity);
        CloseableHttpResponse response = client.execute(httpPost);
        HttpEntity responseEntity = response.getEntity();
        if (responseEntity != null) {
            String responseBody = EntityUtils.toString(responseEntity);
            System.out.println(responseBody);
        }
    }

    public static void httpHeaderDemo() throws IOException {
        HttpGet httpGet = new HttpGet("http://httpbin.org/get");
        httpGet.setHeader("User-Agent", "MyHttpClient/1.0");
        httpGet.setHeader("Authorization", "Bearer my_token");
        CloseableHttpResponse response = client.execute(httpGet);
        System.out.println(EntityUtils.toString(response.getEntity()));
    }

}

结论： 本文介绍了如何使用HttpClient库进行HTTP请求的常见操作，包括GET请求、POST请求、添加请求参数和请求体、设置请求头等。通过使用HttpClient，我们可以轻松地与服务器进行通信并处理响应数据。希望本文对你理解和使用HttpClient有所帮助！

作者：MerkleJqueryRu
链接：https://juejin.cn/post/7234342980156915769