服务调用初阶详解（RestTemplate、HttpClient）

概述

无论是微服务还是SOA，都面临着服务间的远程调用。

常见的远程调用方式有以下2种：

• RPC： Remote Produce Call远程过程调用，类似的还有RMI（remote method invoke）。自定义数据格式，基于原生TCP通信，速度快，效率高。早期的webservice，现在热门的dubbo，都是RPC的典型代表。
• Http： http其实是一种网络传输协议，基于TCP，规定了数据传输的格式。 现在客户端浏览器与服务端通信基本都是采用Http协议，也可以用来进行远程服务调用。缺点是消息封装臃肿，优势是对服务的提供和调用方没有任何技术限定，自由灵活，更符合微服务理念。现在热门的Rest风格，就可以通过http协议来实现。

如果项目全部采用 Java技术栈，那么使用Dubbo作为微服务架构是一个不错的选择。

如果项目的技术栈多样化，主要采用了Spring和SpringBoot框架，那么SpringCloud搭建微服务是不二之选，使用Http方式来实现服务间调用。

java开发中，使用http连接，访问第三方网络接口，通常使用的连接工具为RestTemplate、HttpClient和OKHttp。

RestTemplate

概述及依赖

HttpClient和OKHttp两种连接工具，使用起来比较复杂，如果使用spring框架，可以使用restTemplate来进行http连接请求。

restTemplate默认的连接方式是java中的HttpConnection，可以使用ClientHttpRequestFactory指定不同的HTTP连接方式。

依赖

<dependency>
    <groupId>org.springframeworkgroupId>
    <artifactId>spring-webartifactId>
    <version>5.2.2.RELEASEversion>
dependency>
<dependency>
    <groupId>org.apache.httpcomponentsgroupId>
    <artifactId>httpclientartifactId>
    <version>4.5.7version>
dependency>

配置类

基础配置

@Configuration
public class RestTemplateConfig {
   @Bean
   public RestTemplate restTemplate(ClientHttpRequestFactory factory) {
       return new RestTemplate(factory);
   }
    
   @Bean
   public ClientHttpRequestFactory simpleClientHttpRequestFactory() {
       SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();
       factory.setReadTimeout(150 * 1000); // ms
       factory.setConnectTimeout(150 * 1000); // ms
       return factory;
   }
}

进阶配置

import org.apache.http.client.HttpClient;
import org.apache.http.conn.HttpClientConnectionManager;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

@Configuration
public class RestTemplateConfig {
    
    /**
     * http连接管理器
     */
    @Bean
    public HttpClientConnectionManager poolingHttpClientConnectionManager() {
        /*// 注册http和https请求
        Registry registry = RegistryBuilder.create()
                .register("http", PlainConnectionSocketFactory.getSocketFactory())
                .register("https", SSLConnectionSocketFactory.getSocketFactory())
                .build();
        PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager(registry);*/
        
        PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager();
        // 最大连接数
        poolingHttpClientConnectionManager.setMaxTotal(500);
        // 同路由并发数（每个主机的并发）
        poolingHttpClientConnectionManager.setDefaultMaxPerRoute(100);
        return poolingHttpClientConnectionManager;
    }
    
    /**
     * HttpClient
     * @param poolingHttpClientConnectionManager
     */
    @Bean
    public HttpClient httpClient(HttpClientConnectionManager poolingHttpClientConnectionManager) {
        HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
        // 设置http连接管理器
        httpClientBuilder.setConnectionManager(poolingHttpClientConnectionManager);
        
        /*// 设置重试次数，默认是3次，没有开启
        httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler(3, true));*/
        
        // 设置默认请求头
        /*List
 headers = new ArrayList<>();
        headers.add(new BasicHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.16 Safari/537.36"));
        headers.add(new BasicHeader("Accept-Encoding", "gzip,deflate"));
        headers.add(new BasicHeader("Accept-Language", "zh-CN"));
        headers.add(new BasicHeader("Connection", "Keep-Alive"));
        headers.add(new BasicHeader("Content-type", "application/json;charset=UTF-8"));
        httpClientBuilder.setDefaultHeaders(headers);*/
        
        return httpClientBuilder.build();
    }
    
    /**
     * 请求连接池配置
     * @param httpClient
     */
    @Bean
    public ClientHttpRequestFactory clientHttpRequestFactory(HttpClient httpClient) {
        HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();
        // httpClient创建器
        clientHttpRequestFactory.setHttpClient(httpClient);
        // 连接超时时间/毫秒（连接上服务器(握手成功)的时间，超出抛出connect timeout）
        clientHttpRequestFactory.setConnectTimeout(5 * 1000);
        // 数据读取超时时间(socketTimeout)/毫秒（服务器返回数据(response)的时间，超过抛出read timeout）
        clientHttpRequestFactory.setReadTimeout(10 * 1000);
        // 从连接池获取请求连接的超时时间，不宜过长，必须设置/毫秒（超时间未拿到可用连接，会抛出org.apache.http.conn.ConnectionPoolTimeoutException: Timeout waiting for connection from pool）
        clientHttpRequestFactory.setConnectionRequestTimeout(10 * 1000);
        return clientHttpRequestFactory;
    }
    
    /**
     * rest模板
     */
    @Bean
    public RestTemplate restTemplate(ClientHttpRequestFactory clientHttpRequestFactory) {
        // 配置请求工厂
        return new RestTemplate(clientHttpRequestFactory);
    }
    
}

使用

实体类

@Data
@Builder
@NoArgsConstrutor
@AllArgsConstrutor
public class BaseResponse<TempUser> implements Serializable {
    private static final long serialVersionUID  = 1L;
    
    private String responseCode;
    private String responseMessage;
    private List<TempUser> responseData;
}

@Data
@Builder
@NoArgsConstrutor
@AllArgsConstrutor
public class TempUser implements Serializable {
    private static final long serialVersionUID  = 1L;
    
    private String userName;   
    private Integer age;
}

GET请求

普通访问

BaseResponse result = restTemplate.getForObject(
    "http://localhost:8080/cs-admin/rest/getUser?userName=张三&age=18", BaseResponse.class);

返回HTTP状态

ResponseEntity<BaseResponse> responseEntity = restTemplate.getForEntity(
    "http://localhost:8080/cs-admin/rest/getUser?userName=张三&age=18", TempUser.class);
// 获取状态对象
HttpStatus httpStatus = responseEntity.getStatusCode();
// 获取状态码
int statusCodeValue = responseEntity.getStatusCodeValue();
// 获取headers
HttpHeaders httpHeaders = responseEntity.getHeaders();
// 获取body
BaseResponse result = responseEntity.getBody();

映射请求参数

Map<String, Object> paramMap = new HashMap<>();
paramMap.put("userName", "张三");
paramMap.put("age", 18);
BaseResponse result = restTemplate.getForObject(
    "http://localhost:8080/cs-admin/rest/getUser?userName={userName}&age={age}", 
    BaseResponse.class, paramMap);

POST请求

普通访问接口

TempUser param = new TempUser();
param.setUserName("张三");
param.setAge(18);
BaseResponse result = restTemplate.postForObject("http://localhost:8080/cs-admin/rest/getPostUser", 
                                             param, BaseResponse.class);

带HEAD访问接口

// 请求头信息
HttpHeaders headers = new HttpHeaders();
//headers.setContentType(MediaType.valueOf("application/json;charset=UTF-8"));
headers.setContentType(MediaType.APPLICATION_JSON_UTF8);
//headers.add("headParam1", "headParamValue");

// 请求体内容
TempUser param = new TempUser();
param.setUserName("张三");
param.setAge(18);

// 组装请求信息
HttpEntity<TempUser> httpEntity=new HttpEntity<>(param, headers);

BaseResponse result = restTemplate.postForObject("http://localhost:8080/cs-admin/rest/getPostUser", 
                                             httpEntity, BaseResponse.class);

无请求体的访问：仅method为post，传参方式仍然为get的param方式

Map<String, Object> paramMap = new HashMap<>();
paramMap.put("userName", "张三");
paramMap.put("age", 18);
BaseResponse result = restTemplate.postForObject(
    "http://localhost:8080/cs-admin/rest/getPostUserNoBody?userName={userName}&age={age}", 
    null, BaseResponse.class, paramMap);
System.out.println(result);

上传文件

后台接口代码：

@RequestMapping("uploadFile")
public TempUser uploadFile(HttpServletRequest request, TempUser form) {
    MultipartHttpServletRequest multipartHttpServletRequest = (MultipartHttpServletRequest) request;
    //获取文件信息
    MultipartFile multipartFile = multipartHttpServletRequest.getFile("file");
    TempUser tempUser = new TempUser();
    if (multipartFile != null) {
        tempUser.setUserName(form.getUserName() + " " + multipartFile.getOriginalFilename());
    }
    if(form!=null){
        tempUser.setAge(form.getAge());
    }
    return tempUser;
}

访问方式：

// 文件
FileSystemResource file=new FileSystemResource("D:\\Elasticsearch权威指南（中文版）.pdf");

// 设置请求内容
MultiValueMap<String, Object> param=new LinkedMultiValueMap<>();
param.add("file", file);
// 其他参数
param.add("userName", "张三");
param.add("age", 18);

// 组装请求信息
HttpEntity<MultiValueMap<String, Object>> httpEntity=new HttpEntity<>(param);

// 发送请求
TempUser result = restTemplate.postForObject("http://localhost:8080/cs-admin/rest/uploadFile", 
                                             httpEntity, TempUser.class);

HttpClient

概述

HttpClient 通过连接池创建连接：

1. 管理连接的基本单位是Route（路由），每个路由上都会维护一定数量的HTTP连接
2. 每次调用后必须执行 releaseConnection
3. 路由可以理解为客户端机器到目标机器的一条线路
4. 如果不给 httpclient配置指定的连接管理器，httpclient会自动使用PoolingHttpClientConnectionManager作为连接管理器。
5. PoolingHttpClientConnectionManager默认的maxConnPerRoute和maxConnTotal分别是是2和20。也就是对于每个服务器最多只会维护2个连接，看起来有点少。所以，在日常使用时我们尽量使用自己配置的连接管理器比较好。

连接池：

• 连接池技术作为创建和管理连接的缓冲池技术。
• 连接池管理的对象是长连接
• 有长连接的优势

**长连接：**是指客户端与服务器端一旦建立连接以后，可以进行多次数据传输而不需重新建立连接，

• 优势：
  • 省去了每次数据传输连接建立的时间开销
  • 资源的访问控制

**短连接：**每次数据传输都需要客户端和服务器端建立一次连接

使用

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，参数则必须用NameValuePair[]数组存储
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

依赖：

<dependency>
    <groupId>org.apache.httpcomponentsgroupId>
    <artifactId>httpclientartifactId>
    <version>4.5.2version>
dependency>
    <dependency>
    <groupId>org.apache.httpcomponentsgroupId>
    <artifactId>httpclient-cacheartifactId>
    <version>4.5.2version>
dependency>
    <dependency>
    <groupId>org.apache.httpcomponentsgroupId>
    <artifactId>httpmimeartifactId>
    <version>4.5.2version>
dependency>

java工具类

import com.alibaba.fastjson.JSON;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
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.config.RequestConfig;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import org.slf4j.Logger;

import java.net.URI;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * HttpClient 工具类
 */
@Slf4j
public class HttpClientUtil {
    public static final String APPLICATION_JSON_VALUE = "application/json";
    private static final Logger logger = log;
    private static final Integer CONN_TIME_OUT = 3000;// 超时时间豪秒
    private static final Integer SOCKET_TIME_OUT = 10000;
    /** 每个路由的最大请求数，默认2 */
    private static final Integer DEFAULT_MAX_PER_ROUTE = 40;
    /** 最大连接数，默认20 */
    private static final Integer MAX_TOTAL = 400;
    
    private static HttpClient httpClient;

    static {
        // 请求配置
        RequestConfig requestConfig = RequestConfig.custom()
                .setConnectTimeout(CONN_TIME_OUT)
                .setConnectionRequestTimeout(CONN_TIME_OUT)
                .setSocketTimeout(SOCKET_TIME_OUT)
                .build();

        // 管理 http连接池
        PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
        cm.setDefaultMaxPerRoute(DEFAULT_MAX_PER_ROUTE);
        cm.setMaxTotal(MAX_TOTAL);

        httpClient = HttpClients.custom()
            .setConnectionManager(cm)
            .setDefaultRequestConfig(requestConfig)
            .build();
    }

    /**
     * Get请求
     */
    public static String requestGet(String url, Map<String, String> paramsMap) throws Exception {
        logger.info("GET request  url:{} params:{}", url, paramsMap);
        Long start = System.currentTimeMillis();

        List<NameValuePair> params = initParams(paramsMap);
        // Get请求
        HttpGet httpGet = new HttpGet(url);

        try {
            // 设置参数
            String str = EntityUtils.toString(new UrlEncodedFormEntity(params, StandardCharsets.UTF_8));
            String uriStr = StringUtils.isEmpty(str) ? 
                httpGet.getURI().toString() : httpGet.getURI().toString() + "?" + str;
            httpGet.setURI(new URI(uriStr));
            // 发送请求
            HttpResponse response = httpClient.execute(httpGet);
            
            logger.info("GET request  url:{} response:{} time:{}",
                    url, response, System.currentTimeMillis() - start);

            // 获取返回数据
            return getSuccessRetFromResp(response, url, JSON.toJSONString(paramsMap));
        } finally {
            // 必须释放连接，不然连接用完后会阻塞
            httpGet.releaseConnection();
        }
    }

    /**
     * Post请求，Map格式数据
     */
    public static String requestPost(String url, Map<String, String> paramsMap) throws Exception {
        logger.info("POST request  url:{} params:{}", url, paramsMap);
        Long start = System.currentTimeMillis();

        List<NameValuePair> params = initParams(paramsMap);

        HttpPost httpPost = new HttpPost(url);

        try {
            httpPost.setEntity(new UrlEncodedFormEntity(params, Consts.UTF_8));

            HttpResponse response = httpClient.execute(httpPost);
            
            logger.info("POST request  url:{} response:{}  time:{}",
                    url, response, System.currentTimeMillis() - start);

            String retStr = getSuccessRetFromResp(response, url, JSON.toJSONString(paramsMap));

            return retStr;
        } finally {
            httpPost.releaseConnection();
        }
    }

    /**
     * Post请求，json格式数据
     *
     */
    public static String requestPostJsonStr(String url, String json) throws Exception {
        logger.info("POST request  url:{} params:{}", url, json);
        long start = System.currentTimeMillis();

        HttpPost httpPost = new HttpPost(url);

        try {
            StringEntity entity = new StringEntity(json, Consts.UTF_8);
            entity.setContentType(APPLICATION_JSON_VALUE);
            httpPost.setEntity(entity);

            HttpResponse response = httpClient.execute(httpPost);

            logger.info("POST request  url:{} response:{}  time:{}", 
                        url, response, System.currentTimeMillis() - start);

            return getSuccessRetFromResp(response, url, json);
        } finally {
            // 资源释放
            httpPost.releaseConnection();
        }

    }

    /**
     * post Object格式数据
     */
    public static String requestPostJson(String url, Object obj) throws Exception {
        String params = JSON.toJSONString(obj);
        return requestPostJsonStr(url, params);
    }

    private static String getSuccessRetFromResp(HttpResponse response, String url, String params) throws Exception {
        String retStr = "";
        // 检验状态码，如果成功接收数据
        int code = response.getStatusLine().getStatusCode();

        if (code == 200) {
            retStr = EntityUtils.toString(response.getEntity(), Consts.UTF_8);
        } else {
            throw new RuntimeException(String.format("Http request error:%s, url:%s, params:%s", response, url, params));
        }

        logger.info("Http request retStr:{}. url:{}", retStr, url);
        return retStr;
    }

    private static List<NameValuePair> initParams(Map<String, String> paramsMap) {
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        if (paramsMap == null)
            return params;

        for (Map.Entry<String, String> entry : paramsMap.entrySet()) {
            params.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
        }

        return params;
    }
}