HttpClient

一、初识HttpClient

HttpClient 是Apache Jakarta Common 下的子项目，可以用来提供高效的、最新的、功能丰富的支持 HTTP 协议的客户端编程工具包，并且它支持 HTTP 协议最新的版本和建议。

----百度百科

就是用来发送http请求或者解析http响应的。

二、HttpClient请求

当然在使用之前，需要导包，使用maven（不使用maven就要自己取下jar包，apache官网就有）：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
</dependency>

包导入之后，一般分为六步：

1. 创建HttpClient实例
2. 创建某种连接方法的实例
3. 调用HttpClient实例的execute方法来执行请求方法
4. 读取response
5. 释放连接，无论执行方法是否成功

2.1 GET请求

我们先以GET请求为例

1. 创建HttpClient实例

   CloseableHttpClient httpClient = HttpClients.createDefault();
   

2. 创建GET请求方法实例

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

3. 调用HttpClient实例执行GET实例，返回response

   CloseableHttpResponse response = httpClient.execute(httpGet);
   

4. 解析response

   // 获取状态码
   int status = response.getStatusLine().getStatusCode();
   // 获取实例
   HttpEntity entity = response.getEntity();
   // 获取html
   String html = EntityUtils.toString(entity);
   

5. 释放连接

   response.close();
   httpClient.close();
   

完整代码：

package vip.yangsf;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.ResponseHandler;
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.DecompressingHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.w3c.dom.Document;
import sun.plugin.dom.html.HTMLDocument;
import java.io.IOException;
public class GetTest {
    public static void main(String[] args) throws IOException {
        // 1. 创建HttpClient实例
        CloseableHttpClient httpClient = HttpClients.createDefault();
        // 2. 创建GET请求方法实例
        HttpGet httpGet = new HttpGet("http://test.yangsf.vip");
        // 3. 调用HttpClient实例来执行GET请求方法，得到response
        CloseableHttpResponse response = httpClient.execute(httpGet);
        // 4. 读response，判断是否访问成功 2xx表示 成功。
        int status = response.getStatusLine().getStatusCode();
        if (status >= 200 && status < 300) {
            // 对得到后的实例可以进行处理，例如读取回复体，读取html
            HttpEntity entity = response.getEntity();
            System.out.println(response);
            System.out.println("=======================");
            String html = EntityUtils.toString(entity);
            System.out.println(html);
        } else {
            throw new ClientProtocolException("Unexpected response status: " + status);
        }
        // 6. 释放连接
        response.close();
        httpClient.close();
    }
}

2.2 POST请求

步骤基本上一模一样，只不过可以设置让post带上参数：

httpPost.setEntity(new StringEntity("this is Post"));

package vip.yangsf;
import com.sun.xml.internal.ws.api.pipe.ContentType;
import org.apache.http.HttpEntity;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
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;
public class PostTest {
        public static void main(String... args) throws IOException {
            // 1. 创建HttpClient实例
            CloseableHttpClient httpclient = HttpClients.createDefault();
            // 2. 创建HttpPost实例
            HttpPost httpPost = new HttpPost("http://httpbin.org/post");
            httpPost.setEntity(new StringEntity("this is Post"));
            // 3. 调用HttpClient实例来执行HttpPost实例
            CloseableHttpResponse response = httpclient.execute(httpPost);
            // 4. 读 response
            int status = response.getStatusLine().getStatusCode();
            if (status >= 200 && status < 300) {
                HttpEntity entity = response.getEntity();
                System.out.println(response);
                System.out.println("===================");
                String html = EntityUtils.toString(entity);
                System.out.println(html);
            } else {
                throw new ClientProtocolException("Unexpected response status: " + status);
            }
            // 5. 释放连接
            response.close();
            httpclient.close();
        }
}

效果：

其他请求方法比如put，delete等也是大同小异。

三、HttpClient提交表单

提交表单一共就这几步：

1. 创建http实例
2. 创建Post请求
3. 设置表单参数并让Post携带
4. 执行请求，获取响应
5. 解析响应
6. 关闭资源

package vip.yangsf;
import org.apache.http.Consts;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
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;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class FormSubmitTest {
    public static void main(String[] args) throws IOException {
        // 1. 创建HttpClient实例
        CloseableHttpClient httpClient = HttpClients.createDefault();
        // 2. 设置表单参数
        List<NameValuePair> kv =  new ArrayList<>();
        kv.add(new BasicNameValuePair("name", "root"));
        kv.add(new BasicNameValuePair("password", "123456"));
        // 3. 创建HttpPost实例
        HttpPost httpPost = new HttpPost("http://httpbin.org/post");
        // 4. 让Post携带表单参数
        httpPost.setEntity(new UrlEncodedFormEntity(kv, Consts.UTF_8));
        // 5. 获取HttpResponse响应
        CloseableHttpResponse response = httpClient.execute(httpPost);
        // 6. 读response
        System.out.println(EntityUtils.toString(response.getEntity()));
        // 7. 释放资源
        response.close();
        httpClient.close();
    }
}

结果：

HttpClient最基本的用法就是这些。之后可以去官方文档查阅更多的用法，比如HttpClient还可以获取证书，上传文件等等。