Java中使用HttpClient调用api

java中可以使用3种方式调用api

• HttpURLConnection
• HttpClient
• RestTemplate

这里要讲的是HttpClient的方式。

一.简介

HttpClient是Apache Jakarta Common下的子项目，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。HttpClient已经应用在很多的项目中，比如Apache Jakarta上很著名的另外两个开源项目Cactus和HTMLUnit都使用了HttpClient。

二.特性

1. 基于标准、纯净的java语言。实现了Http1.0和Http1.1

2. 以可扩展的面向对象的结构实现了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。

3. 支持HTTPS协议。

4. 通过Http代理建立透明的连接。

5. 利用CONNECT方法通过Http代理建立隧道的https连接。

6. Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO/Kerberos认证方案。

7. 插件式的自定义认证方案。

8. 便携可靠的套接字工厂使它更容易的使用第三方解决方案。

9. 连接管理器支持多线程应用。支持设置最大连接数，同时支持设置每个主机的最大连接数，发现并关闭过期的连接。

10. 自动处理Set-Cookie中的Cookie。

11. 插件式的自定义Cookie策略。

12. Request的输出流可以避免流中内容直接缓冲到socket服务器。

13. Response的输入流可以有效的从socket服务器直接读取相应内容。

14. 在http1.0和http1.1中利用KeepAlive保持持久连接。

15. 直接获取服务器发送的response code和 headers。

16. 设置连接超时的能力。

17. 实验性的支持http1.1 response caching。

18. 源代码基于Apache License 可免费获取

三.使用方法

使用HttpClient发送请求、接收响应很简单，一般需要如下几步即可。

1.  创建HttpClient对象。
2. 创建请求方法的实例，并指定请求URL。如果需要发送GET请求，创建HttpGet对象；如果需要发送POST请求，创建HttpPost对象。
3. 如果需要发送请求参数，可调用HttpGet、HttpPost共同的setParams(HetpParams params)方法来添加请求参数；对于HttpPost对象而言，也可调用setEntity(HttpEntity entity)方法来设置请求参数。
4. 调用HttpClient对象的execute(HttpUriRequest request)发送请求，该方法返回一个HttpResponse。
5. 调用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可获取服务器的响应头；调用HttpResponse的getEntity()方法可获取HttpEntity对象，该对象包装了服务器的响应内容。程序可通过该对象获取服务器的响应内容。
6. 释放连接。无论执行方法是否成功，都必须释放连接

四.实例

package com.test;
 
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.KeyManagementException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateException;
import java.util.ArrayList;
import java.util.List;
 
import javax.net.ssl.SSLContext;
 
import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.ParseException;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
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.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.conn.ssl.SSLContexts;
import org.apache.http.conn.ssl.TrustSelfSignedStrategy;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.entity.mime.content.StringBody;
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 org.junit.Test;
 
public class HttpClientTest {
 
    @Test
    public void jUnitTest() {
        get();
    }
 
    /**
     * HttpClient连接SSL
     */
    public void ssl() {
        CloseableHttpClient httpclient = null;
        try {
            KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
            FileInputStream instream = new FileInputStream(new File("d:\tomcat.keystore"));
            try {
                // 加载keyStore d:\tomcat.keystore  
                trustStore.load(instream, "123456".toCharArray());
            } catch (CertificateException e) {
                e.printStackTrace();
            } finally {
                try {
                    instream.close();
                } catch (Exception ignore) {
                }
            }
            // 相信自己的CA和所有自签名的证书
            SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build();
            // 只允许使用TLSv1协议
            SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[] { "TLSv1" }, null,
                    SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);
            httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();
            // 创建http请求(get方式)
            HttpGet httpget = new HttpGet("https://localhost:8443/myDemo/Ajax/serivceJ.action");
            System.out.println("executing request" + httpget.getRequestLine());
            CloseableHttpResponse response = httpclient.execute(httpget);
            try {
                HttpEntity entity = response.getEntity();
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                if (entity != null) {
                    System.out.println("Response content length: " + entity.getContentLength());
                    System.out.println(EntityUtils.toString(entity));
                    EntityUtils.consume(entity);
                }
            } finally {
                response.close();
            }
        } catch (ParseException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (KeyManagementException e) {
            e.printStackTrace();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (KeyStoreException e) {
            e.printStackTrace();
        } finally {
            if (httpclient != null) {
                try {
                    httpclient.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
 
    /**
     * post方式提交表单（模拟用户登录请求）
     */
    public void postForm() {
        // 创建默认的httpClient实例.  
        CloseableHttpClient httpclient = HttpClients.createDefault();
        // 创建httppost  
        HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");
        // 创建参数队列  
        List formparams = new ArrayList();
        formparams.add(new BasicNameValuePair("username", "admin"));
        formparams.add(new BasicNameValuePair("password", "123456"));
        UrlEncodedFormEntity uefEntity;
        try {
            uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");
            httppost.setEntity(uefEntity);
            System.out.println("executing request " + httppost.getURI());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    System.out.println("--------------------------------------");
                    System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));
                    System.out.println("--------------------------------------");
                }
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e1) {
            e1.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 关闭连接,释放资源  
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
 
    /**
     * 发送 post请求访问本地应用并根据传递参数不同返回不同结果
     */
    public void post() {
        // 创建默认的httpClient实例.  
        CloseableHttpClient httpclient = HttpClients.createDefault();
        // 创建httppost  
        HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");
        // 创建参数队列  
        List formparams = new ArrayList();
        formparams.add(new BasicNameValuePair("type", "house"));
        UrlEncodedFormEntity uefEntity;
        try {
            uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");
            httppost.setEntity(uefEntity);
            System.out.println("executing request " + httppost.getURI());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    System.out.println("--------------------------------------");
                    System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));
                    System.out.println("--------------------------------------");
                }
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e1) {
            e1.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 关闭连接,释放资源  
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
 
    /**
     * 发送 get请求
     */
    public void get() {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            // 创建httpget.  
            HttpGet httpget = new HttpGet("http://www.baidu.com/");
            System.out.println("executing request " + httpget.getURI());
            // 执行get请求.  
            CloseableHttpResponse response = httpclient.execute(httpget);
            try {
                // 获取响应实体  
                HttpEntity entity = response.getEntity();
                System.out.println("--------------------------------------");
                // 打印响应状态  
                System.out.println(response.getStatusLine());
                if (entity != null) {
                    // 打印响应内容长度  
                    System.out.println("Response content length: " + entity.getContentLength());
                    // 打印响应内容  
                    System.out.println("Response content: " + EntityUtils.toString(entity));
                }
                System.out.println("------------------------------------");
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 关闭连接,释放资源  
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
 
    /**
     * 上传文件
     */
    public void upload() {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceFile.action");
 
            FileBody bin = new FileBody(new File("F:\image\sendpix0.jpg"));
            StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);
 
            HttpEntity reqEntity = MultipartEntityBuilder.create().addPart("bin", bin).addPart("comment", comment).build();
 
            httppost.setEntity(reqEntity);
 
            System.out.println("executing request " + httppost.getRequestLine());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                HttpEntity resEntity = response.getEntity();
                if (resEntity != null) {
                    System.out.println("Response content length: " + resEntity.getContentLength());
                }
                EntityUtils.consume(resEntity);
            } finally {
                response.close();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

本实例是采用HttpClient4.3版本。

参考网址：

https://blog.csdn.net/wangpeng047/article/details/19624529