1 前言

HttpClient是由Apache基金会出品的一个传输库，通过该库可以发送和接收Http消息，在JDK11中被集成。

由于最近业务可能需要使用，就学习了httpclient的简单用法，下面就从最简单的get、post请求入手。

项目需要maven坐标如下：

<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
  	<groupId>com.alibaba</groupId>
  	<artifactId>fastjson</artifactId>
  	<version>1.2.58</version>
</dependency>

<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
<dependency>
	<groupId>org.apache.httpcomponents</groupId>
  	<artifactId>httpclient</artifactId>
  	<version>4.5.6</version>
</dependency>

2 HttpGet方法

2.1 步骤

get方法通常用于检索数据，httpclient中提供了httpGet类，代表get请求方法，通常请求流程如下：

创建HttpClient对象

CloseableHttpClient httpClient = HttpClients.createDefault();
创建HttpGet对象

HttpGet httpGet = new HttpGet("http://www.baidu.com/");
执行get请求

HttpResponse httpResponse = httpClient.execute(httpGet);

2.2 示例

// 1 创建HttpClient对象
CloseableHttpClient httpClient = HttpClients.createDefault();
// 2 创建一个HttpGet对象
HttpGet httpGet = new HttpGet("http://www.baidu.com/");
// 3 执行获取请求
HttpResponse httpResponse = httpClient.execute(httpGet);

Scanner sc = new Scanner(httpResponse.getEntity().getContent());
System.out.println(httpResponse.getStatusLine());
while (sc.hasNext()) { 
   
    System.out.println(sc.nextLine());
}

通过httpResponse.getEntity().getContent()获取页面的信息，该方法返回InputStream

3 HttpPost方法

3.1 步骤

post请求用于向服务端发送数据，httpclient提供了HttpPost类，表示post方法，一般流程如下：

创建HttpClient对象

CloseableHttpClient httpClient = HttpClients.createDefault();
创建HttpPost对象

HttpPost httpPost = new HttpPost(${target});
执行post请求

HttpResponse httpResponse = httpClient.execute(httpPost);

注意：${target}表示字符串uri，例如：http://localhost:8080/post

3.2 示例

由于post请求用于发送数据，因此需要一个能接受数据并处理的接口，此处用SpringBoot框架编写，先看示例

// 1 创建HttpClient对象
CloseableHttpClient httpClient = HttpClients.createDefault();
// 2 创建HttpPost对象
HttpPost httpPost = new HttpPost("http://localhost:8080/post");

// 添加请求头信息，告诉服务器要发送的数据类型
httpPost.addHeader("Accept", "application/json");
httpPost.addHeader("content-Type","application/json;charset=UTF-8");

// 数据实体
JSONObject params = new JSONObject();
params.put("name", "wzy");
params.put("gender", "male");
params.put("age", "22");

httpPost.setEntity(new StringEntity(params.toString(), StandardCharsets.UTF_8));

// 3 执行获取请求
HttpResponse httpResponse = httpClient.execute(httpPost);

Scanner sc = new Scanner(httpResponse.getEntity().getContent());
System.out.println(httpResponse.getStatusLine());
while (sc.hasNext()) { 
   
    System.out.print(sc.nextLine());
}

注意 httpPost.addHeader()必须制定消息头，否则后端报错：Not Supported Type……，Controller API：

private List<Person> message = new ArrayList<>(10);

@PostMapping("/post")
@ResponseBody
public String postTest(@RequestBody Person person) { 
   
    message.add(person);
    return "hi,服务端已收到信息：" + person.toString();
}

@GetMapping("/get")
@ResponseBody
public List getTest() { 
   
    return message;
}