服务调用初阶详解（RestTemplate、HttpClient）

冷不防 2023-09-29 15:46 18阅读 0赞

# 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.springframework</groupId>
        <artifactId>spring-web</artifactId>
        <version>5.2.2.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.5.7</version>
    </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<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory>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<Header> 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.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.5.2</version>
    </dependency>
        <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient-cache</artifactId>
        <version>4.5.2</version>
    </dependency>
        <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpmime</artifactId>
        <version>4.5.2</version>
    </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;
        }
    }