浅析几种Java Http请求库的使用：HttpURLConnection、RestTemplate、OKhttp、Feign/OpenFeign

　　转载于：https://www.modb.pro/db/69232

　　java常见的http请求库有HttpURLConnection、httpclient、RestTemplate、OKhttp，更高层次封装的 feign、retrofit

一、HttpURLConnection

HttpURLConnection 是 JDK 自带的标准库;

【优点】：不需要引入额外的依赖

【缺点】：缺乏连接池管理、域名机械控制等特性支持，在java9才支持 HTTP/2

public class HttpUrlConnectionDemo {
    public static void main(String[] args) throws Exception {
        String urlString = "https://httpbin.org/post";
        String bodyString = "password=e10adc3949ba59abbe56e057f20f883e&username=test3";
 
        URL url = new URL(urlString);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("POST");
        conn.setDoOutput(true);
 
        OutputStream os = conn.getOutputStream();
        os.write(bodyString.getBytes("utf-8"));
        os.flush();
        os.close();
 
        if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {
            InputStream is = conn.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            StringBuilder sb = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
            System.out.println("rsp:" + sb.toString());
        } else {
            System.out.println("rsp code:" + conn.getResponseCode());
        }
    }
}

二、OkHttp

【优点】：OkHttp 接口设计友好，支持 HTTP/2，并且在弱网和无网环境下有自动检测和恢复机制，因此，是当前 Android APP 开发中使用最广泛的 HTTP clilent lib 之一。

当网络出现问题的时候 OkHttp 依然坚守自己的职责，它会自动恢复一般的连接问题，如果你的服务有多个IP地址，当第一个IP请求失败时，OkHttp 会交替尝试你配置的其他IP，OkHttp使用现代TLS技术(SNI, ALPN)初始化新的连接，当握手失败时会回退到TLS 1.0。

1、导入依赖

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>3.10.0</version>
</dependency>

2、简单使用

import okhttp3.*;
import org.apache.http.util.CharsetUtils;
import java.util.HashMap;
import java.util.Map;

public class OkHttpDemo {
    OkHttpClient client = new OkHttpClient();
 
    private String sendPostForm(String url, final Map<String, String> params) throws Exception {
        FormBody.Builder builder = new FormBody.Builder(CharsetUtils.get("UTF-8"));
        if (params != null) {
            for (Map.Entry<String, String> entry: params.entrySet()) {
                builder.add(entry.getKey(), entry.getValue());
            }
        }
        RequestBody requestBody = builder.build();
        Request request = new Request.Builder().url(url).post(requestBody).build();
        return client.newCall(request).execute().body().string();
 
    }
 
    private String sendGet(String url) throws Exception {
        Request request = new Request.Builder().url(url).build();
        return  client.newCall(request).execute().body().string();
    }
 
    public static void main(String[] args) throws Exception {
        OkHttpDemo okHttpDemo = new OkHttpDemo();
        String url = "https://httpbin.org/post";
        params = new HashMap();
        params.put("foo", "bar中文");
        // Post请求
        String rsp = okHttpDemo.sendPostForm(url, params);
        System.out.println("http post rsp:" + rsp);
         // Get请求
        url = "https://httpbin.org/get";
        System.out.println("http get rsp:" + okHttpDemo.sendGet(url));
    }
}

3、项目应用

（1）配置文件

import okhttp3.ConnectionPool;
import okhttp3.OkHttpClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.concurrent.TimeUnit;

@Configuration
public class OkHttpConfiguration {

    @Bean
    public OkHttpClient okHttpClient() {
        return new OkHttpClient.Builder()
                //.sslSocketFactory(sslSocketFactory(), x509TrustManager())
                .retryOnConnectionFailure(false)
                .connectionPool(pool())
                .connectTimeout(30, TimeUnit.SECONDS)
                .readTimeout(30, TimeUnit.SECONDS)
                .writeTimeout(30,TimeUnit.SECONDS)
                .build();
    }

    @Bean
    public X509TrustManager x509TrustManager() {
        return new X509TrustManager() {
            @Override
            public void checkClientTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
            }
            @Override
            public void checkServerTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
            }
            @Override
            public X509Certificate[] getAcceptedIssuers() {
                return new X509Certificate[0];
            }
        };
    }

    @Bean
    public SSLSocketFactory sslSocketFactory() {
        try {
            //信任任何链接
            SSLContext sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, new TrustManager[]{x509TrustManager()}, new SecureRandom());
            return sslContext.getSocketFactory();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (KeyManagementException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * Create a new connection pool with tuning parameters appropriate for a single-user application.
     * The tuning parameters in this pool are subject to change in future OkHttp releases. Currently
     */
    @Bean
    public ConnectionPool pool() {
        return new ConnectionPool(200, 5, TimeUnit.MINUTES);
    }
}

（2）utils 工具类

import okhttp3.*;
import org.apache.commons.lang3.exception.ExceptionUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.util.Iterator;
import java.util.Map;

public class OkHttpUtil{
    private static final Logger logger = LoggerFactory.getLogger(OkHttpUtil.class);
    
    private static OkHttpClient  okHttpClient;

    @Autowired
    public OkHttpUtil(OkHttpClient  okHttpClient) {
        OkHttpUtil.okHttpClient= okHttpClient;
    } 
    
    /**
     * get
     * @param url     请求的url
     * @param queries 请求的参数，在浏览器？后面的数据，没有可以传null
     * @return
     */
    public static  String get(String url, Map<String, String> queries) {
        String responseBody = "";
        StringBuffer sb = new StringBuffer(url);
        if (queries != null && queries.keySet().size() > 0) {
            boolean firstFlag = true;
            Iterator iterator = queries.entrySet().iterator();
            while (iterator.hasNext()) {
                Map.Entry entry = (Map.Entry<String, String>) iterator.next();
                if (firstFlag) {
                    sb.append("?" + entry.getKey() + "=" + entry.getValue());
                    firstFlag = false;
                } else {
                    sb.append("&" + entry.getKey() + "=" + entry.getValue());
                }
            }
        }
        Request request = new Request.Builder()
                .url(sb.toString())
                .build();
        Response response = null;
        try { 
            response = okHttpClient.newCall(request).execute();
            int status = response.code();
            if (response.isSuccessful()) {
                return response.body().string();
            }
        } catch (Exception e) {
            logger.error("okhttp3 put error >> ex = {}", ExceptionUtils.getStackTrace(e));
        } finally {
            if (response != null) {
                response.close();
            }
        }
        return responseBody;
    }

    /**
     * post
     *
     * @param url    请求的url
     * @param params post form 提交的参数
     * @return
     */
    public static String post(String url, Map<String, String> params) {
        String responseBody = "";
        FormBody.Builder builder = new FormBody.Builder();
        //添加参数
        if (params != null && params.keySet().size() > 0) {
            for (String key : params.keySet()) {
                builder.add(key, params.get(key));
            }
        }
        Request request = new Request.Builder()
                .url(url)
                .post(builder.build())
                .build();
        Response response = null;
        try { 
            response = okHttpClient.newCall(request).execute();
            int status = response.code();
            if (response.isSuccessful()) {
                return response.body().string();
            }
        } catch (Exception e) {
            logger.error("okhttp3 post error >> ex = {}", ExceptionUtils.getStackTrace(e));
        } finally {
            if (response != null) {
                response.close();
            }
        }
        return responseBody;
    }

    /**
     * get
     * @param url     请求的url
     * @param queries 请求的参数，在浏览器？后面的数据，没有可以传null
     * @return
     */
    public static String getForHeader(String url, Map<String, String> queries) {
        String responseBody = "";
        StringBuffer sb = new StringBuffer(url);
        if (queries != null && queries.keySet().size() > 0) {
            boolean firstFlag = true;
            Iterator iterator = queries.entrySet().iterator();
            while (iterator.hasNext()) {
                Map.Entry entry = (Map.Entry<String, String>) iterator.next();
                if (firstFlag) {
                    sb.append("?" + entry.getKey() + "=" + entry.getValue());
                    firstFlag = false;
                } else {
                    sb.append("&" + entry.getKey() + "=" + entry.getValue());
                }
            }
        }
        Request request = new Request.Builder()
                .addHeader("key", "value")
                .url(sb.toString())
                .build();
        Response response = null;
        try { 
            response = okHttpClient.newCall(request).execute();
            int status = response.code();
            if (response.isSuccessful()) {
                return response.body().string();
            }
        } catch (Exception e) {
            logger.error("okhttp3 put error >> ex = {}", ExceptionUtils.getStackTrace(e));
        } finally {
            if (response != null) {
                response.close();
            }
        }
        return responseBody;
    }

    /**
     * Post请求发送JSON数据....{"name":"zhangsan","pwd":"123456"}
     * 参数一：请求Url
     * 参数二：请求的JSON
     * 参数三：请求回调
     */
    public static String postJsonParams(String url, String jsonParams) {
        String responseBody = "";
        RequestBody requestBody = RequestBody.create(MediaType.parse("application/json; charset=utf-8"), jsonParams);
        Request request = new Request.Builder()
                .url(url)
                .post(requestBody)
                .build();
        Response response = null;
        try { 
            response = okHttpClient.newCall(request).execute();
            int status = response.code();
            if (response.isSuccessful()) {
                return response.body().string();
            }
        } catch (Exception e) {
            logger.error("okhttp3 post error >> ex = {}", ExceptionUtils.getStackTrace(e));
        } finally {
            if (response != null) {
                response.close();
            }
        }
        return responseBody;
    }

    /**
     * Post请求发送xml数据....
     * 参数一：请求Url
     * 参数二：请求的xmlString
     * 参数三：请求回调
     */
    public static String postXmlParams(String url, String xml) {
        String responseBody = "";
        RequestBody requestBody = RequestBody.create(MediaType.parse("application/xml; charset=utf-8"), xml);
        Request request = new Request.Builder()
                .url(url)
                .post(requestBody)
                .build();
        Response response = null;
        try { 
            response = okHttpClient.newCall(request).execute();
            int status = response.code();
            if (response.isSuccessful()) {
                return response.body().string();
            }
        } catch (Exception e) {
            logger.error("okhttp3 post error >> ex = {}", ExceptionUtils.getStackTrace(e));
        } finally {
            if (response != null) {
                response.close();
            }
        }
        return responseBody;
    }
}

三、RestTemplate

RestTemplate： 是 Spring 提供的用于访问Rest服务的客户端， RestTemplate 提供了多种便捷访问远程Http服务的方法，能够大大提高客户端的编写效率。

1、导入依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

2、关于注入RestTemplate对象

　　RestTemplate 在源码中是没有@Bean注入的，因此，我们不能直接使用如下方式直接注入

@Autowired
private RestTemplate restTemplate;

【解决方案】

（1）方式一：如果要使用，可以编写配置文件自己注入

@Configuration
public class ApiConfig {
    @Bean
    public RestTemplate restTemplate(ClientHttpRequestFactory factory) {
        return new RestTemplate(factory);
    }

    @Bean
    public ClientHttpRequestFactory simpleClientHttpRequestFactory() {
        //默认的是JDK提供http连接，需要的话可以//通过setRequestFactory方法替换为例如Apache HttpComponents、Netty或//OkHttp等其它HTTP library。
        SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();
        factory.setReadTimeout(5000);//单位为ms
        factory.setConnectTimeout(5000);//单位为ms
        return factory;
    }
}

（2）也可以通过自己新建对象直接使用

RestTemplate restTemplate = new RestTemplate();

3、如何使用

（1）Get 请求

// 方式一
Notice notice = restTemplate.getForObject("http://fantj.top/notice/list/{1}/{2}", Notice.class,1,5);

// 方式二
Map<String,String> map = new HashMap();
map.put("start","1");
map.put("page","5");
Notice notice = restTemplate.getForObject("http://fantj.top/notice/list/", Notice.class,map);

（2）Post 请求

// 方式一
String url = "http://demo/api/book/";
HttpHeaders headers = new HttpHeaders();
MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8");
headers.setContentType(type);
String requestJson = "{...}";
HttpEntity<String> entity = new HttpEntity<String>(requestJson,headers);
String result = restTemplate.postForObject(url, entity, String.class);
System.out.println(result);

// 方式二
String url = "http://47.xxx.xxx.96/register/checkEmail";
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
MultiValueMap<String, String> map= new LinkedMultiValueMap<>();
map.add("email", "844072586@qq.com");

HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(map, headers);
ResponseEntity<String> response = restTemplate.postForEntity( url, request , String.class );
System.out.println(response.getBody());

四、Feign/OpenFeign

　　可以看这篇：Spring Cloud OpenFeign详解  ——  https://blog.csdn.net/taiyangdao/article/details/81359394