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RestTemplate简介

RestTemplate是Spring3.0后开始提供的用于访问 Rest 服务的轻量级客户端，相较于传统的HttpURLConnection、Apache HttpClient、OkHttp等框架，RestTemplate大大简化了发起HTTP请求以及处理响应的过程。

RestTemplate只是对其它Rest客户端的一个封装，本身并没有自己的实现。

RestTemplate默认实现是HttpURLConnection，这是JDK自带的REST客户端实现。 引入哪种Http客户端的Jar包，就会使用哪种Http客户端的实现。

相关Http客户端Maven依赖

       
    
     com.squareup.okhttp3
        
    
     okhttp
        
    
     4.4.0
    
   
       
    
     org.apache.httpcomponents
        
    
     httpclient
        
    
     4.5.11
    
   

RestTemplate配置

RestTemplate包含以下几个部分：

• HttpMessageConverter 对象转换器
• ClientHttpRequestFactory 默认是 JDK的HttpURLConnection
• ResponseErrorHandler 异常处理
• ClientHttpRequestInterceptor 请求拦截器

使用HttpClient作为实现

首先需要引入HttpClient的Maven依赖。

import org.apache.http.client.HttpClient;import org.apache.http.config.Registry;import org.apache.http.config.RegistryBuilder;import org.apache.http.conn.socket.ConnectionSocketFactory;import org.apache.http.conn.socket.PlainConnectionSocketFactory;import org.apache.http.conn.ssl.NoopHostnameVerifier;import org.apache.http.conn.ssl.SSLConnectionSocketFactory;import org.apache.http.impl.client.DefaultHttpRequestRetryHandler;import org.apache.http.impl.client.HttpClientBuilder;import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;import org.apache.http.ssl.SSLContextBuilder;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.beans.factory.annotation.Value;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;import org.springframework.http.converter.HttpMessageConverter;import org.springframework.http.converter.StringHttpMessageConverter;import org.springframework.web.client.DefaultResponseErrorHandler;import org.springframework.web.client.RestTemplate;import javax.net.ssl.HostnameVerifier;import javax.net.ssl.SSLContext;import java.nio.charset.StandardCharsets;import java.security.KeyManagementException;import java.security.KeyStoreException;import java.security.NoSuchAlgorithmException;import java.util.List;@Configurationpublic class RestClientConfig {
       private static final Logger logger = LoggerFactory.getLogger(RestClientConfig.class);    // 连接池的最大连接数默认为0    @Value("${remote.maxTotalConnect:0}")    private int maxTotalConnect;    // 单个主机的最大连接数    @Value("${remote.maxConnectPerRoute:200}")    private int maxConnectPerRoute;    // 连接超时默认2s    @Value("${remote.connectTimeout:2000}")    private int connectTimeout;    // 读取超时默认30s    @Value("${remote.readTimeout:30000}")    private int readTimeout;    @Bean    public RestTemplate restTemplate() {
           RestTemplate restTemplate = new RestTemplate();        restTemplate.setRequestFactory(clientHttpRequestFactory());        restTemplate.setErrorHandler(new DefaultResponseErrorHandler());        // 设置编码格式为UTF-8        List
   
    > converterList = restTemplate.getMessageConverters();        HttpMessageConverter
     converterTarget = null;        for (HttpMessageConverter
     item : converterList) {
               if (item.getClass() == StringHttpMessageConverter.class) {
                   converterTarget = item;                break;            }        }        if (converterTarget != null) {
               converterList.remove(converterTarget);        }        HttpMessageConverter
     converter = new StringHttpMessageConverter(StandardCharsets.UTF_8);        converterList.add(1, converter);        logger.info("-----restTemplate-----初始化完成");        return restTemplate;    }    @Bean    public HttpComponentsClientHttpRequestFactory clientHttpRequestFactory() {
           try {
               HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();            SSLContext sslContext = new SSLContextBuilder().loadTrustMaterial(null, (arg0, arg1) -> true).build();            httpClientBuilder.setSSLContext(sslContext);            HostnameVerifier hostnameVerifier = NoopHostnameVerifier.INSTANCE;            SSLConnectionSocketFactory sslConnectionSocketFactory = new SSLConnectionSocketFactory(sslContext, hostnameVerifier);            // 注册http和https请求            Registry
    
      socketFactoryRegistry = RegistryBuilder.
     
      create()                    .register("http", PlainConnectionSocketFactory.getSocketFactory())                    .register("https", sslConnectionSocketFactory).build();            // 开始设置连接池            PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry);            // 最大连接数            poolingHttpClientConnectionManager.setMaxTotal(maxTotalConnect);            // 同路由的并发数，路由是对maxTotal的细分            poolingHttpClientConnectionManager.setDefaultMaxPerRoute(maxConnectPerRoute);            httpClientBuilder.setConnectionManager(poolingHttpClientConnectionManager);            httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler(3, true)); // 重试次数            HttpClient httpClient = httpClientBuilder.build();            // 数据读取超时时间            HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(httpClient); // httpClient连接配置            // 连接超时            clientHttpRequestFactory.setConnectTimeout(connectTimeout);            // 读取超时            clientHttpRequestFactory.setReadTimeout(readTimeout);            // 连接不够用的等待时间            clientHttpRequestFactory.setConnectionRequestTimeout(20000);            return clientHttpRequestFactory;        } catch (KeyManagementException | NoSuchAlgorithmException | KeyStoreException e) {
               logger.error("初始化HTTP连接池出错", e);        }        return null;    }}
     
    
   

使用OkHttp作为实现

首先需要引入OkHttp的Maven依赖。

import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.http.client.ClientHttpRequestFactory;import org.springframework.http.client.OkHttp3ClientHttpRequestFactory;import org.springframework.web.client.RestTemplate;@Configurationpublic class RestTemplateConfig {
       @Bean    public RestTemplate restTemplate(ClientHttpRequestFactory factory){
           return new RestTemplate(factory);    }    @Bean    public OkHttp3ClientHttpRequestFactory okHttp3ClientHttpRequestFactory(){
           OkHttp3ClientHttpRequestFactory factory = new OkHttp3ClientHttpRequestFactory();        // 单位：毫秒        factory.setConnectTimeout(10000);        factory.setReadTimeout(10000);        factory.setWriteTimeout(10000);        return factory;    }}

发送GET请求

// 1-getForObject()User user1 = this.restTemplate.getForObject(uri, User.class);// 2-getForEntity()ResponseEntity
   
     responseEntity1 = this.restTemplate.getForEntity(uri, User.class);HttpStatus statusCode = responseEntity1.getStatusCode();HttpHeaders header = responseEntity1.getHeaders();User user2 = responseEntity1.getBody();  // 3-exchange()RequestEntity requestEntity = RequestEntity.get(new URI(uri)).build();ResponseEntity
    
      responseEntity2 = this.restTemplate.exchange(requestEntity, User.class);User user3 = responseEntity2.getBody();
    
   

发送POST请求

// 1-postForObject()User user1 = this.restTemplate.postForObject(uri, user, User.class);// 2-postForEntity()ResponseEntity
   
     responseEntity1 = this.restTemplate.postForEntity(uri, user, User.class);// 3-exchange()RequestEntity
    
      requestEntity = RequestEntity.post(new URI(uri)).body(user);ResponseEntity
     
       responseEntity2 = this.restTemplate.exchange(requestEntity, User.class);
     
    
   

设置HTTP Header

// 1-Content-TypeRequestEntity
   
     requestEntity = RequestEntity        .post(new URI(uri))        .contentType(MediaType.APPLICATION_JSON)        .body(user);// 2-AcceptRequestEntity
    
      requestEntity = RequestEntity        .post(new URI(uri))        .accept(MediaType.APPLICATION_JSON)        .body(user);// 3-OtherRequestEntity
     
       requestEntity = RequestEntity        .post(new URI(uri))        .header("Authorization", "Basic " + base64Credentials)        .body(user);
     
    
   

发送文件

MultiValueMap
   
     multiPartBody = new LinkedMultiValueMap<>();multiPartBody.add("file", new ClassPathResource("/tmp/user.txt"));RequestEntity
    
     
      > requestEntity = RequestEntity        .post(uri)        .contentType(MediaType.MULTIPART_FORM_DATA)        .body(multiPartBody);
     
    
   

下载文件

// 小文件RequestEntity requestEntity = RequestEntity.get(uri).build();ResponseEntity
   
     responseEntity = restTemplate.exchange(requestEntity, byte[].class);byte[] downloadContent = responseEntity.getBody();  // 大文件  ResponseExtractor
    
     
      > responseExtractor = new ResponseExtractor
      
       
        >() {
       @Override    public ResponseEntity
        
          extractData(ClientHttpResponse response) throws IOException { File rcvFile = File.createTempFile("rcvFile", "zip"); FileCopyUtils.copy(response.getBody(), new FileOutputStream(rcvFile)); return ResponseEntity.status(response.getStatusCode()).headers(response.getHeaders()).body(rcvFile); }};File getFile = this.restTemplate.execute(targetUri, HttpMethod.GET, null, responseExtractor);
        
       
      
     
    
   

构建测试用的Http服务

import lombok.Data;@Datapublic class User {
       private Long id;    private String username;    private Integer age;}import com.google.gson.Gson;import lombok.extern.slf4j.Slf4j;import org.springframework.web.bind.annotation.*;@RestController@RequestMapping("/")@Slf4jpublic class DemoController {
       @GetMapping("demo/{id}/{userName}")    public User get(@PathVariable Long id, @PathVariable String userName, Integer age){
           log.info("id:{}, userName:{}, age:{}", id, userName, age);        User user = new User();        user.setId(id);        user.setUsername(userName);        user.setAge(age);        return user;    }    @PostMapping("demo")    public User post(@RequestBody String json){
           log.info("json:{}", json);        Gson gson = new Gson();        User user = gson.fromJson(json, User.class);        return user;    }}

RestTemplate使用

GET请求

在RestTemplate中，发送一个GET请求，有两种方式：getForObject()和getForEntity()。

getForEntity

getForEntity方法的返回值是一个ResponseEntity<T>，ResponseEntity<T>是Spring对HTTP请求响应的封装，包括了几个重要的元素，如响应码、contentType、contentLength、响应消息体等。

示例：

String url = "http://127.0.0.1:8080/demo/{id}/{userName}?age=18";// 方式一ResponseEntity
   
     userResponseEntity = restTemplate.getForEntity(url, User.class, 1001L, "Tom");User user = userResponseEntity.getBody();HttpStatus statusCode = userResponseEntity.getStatusCode();int statusCodeValue = userResponseEntity.getStatusCodeValue();HttpHeaders headers = userResponseEntity.getHeaders();System.out.println("user = " + user + "; statusCode = " + statusCode + "; statusCodeValue = " + statusCodeValue + "; headers = " + headers);// 方式二Map
    
      urlParams = new HashMap<>();urlParams.put("id", 1001L);urlParams.put("userName", "James");ResponseEntity
     
       userResponseEntity2 = restTemplate.getForEntity(url, User.class, urlParams);// 方式三UriComponents uriComponents = UriComponentsBuilder.fromUriString(url).build().expand(1001L, "James").encode();URI uri = uriComponents.toUri();ResponseEntity
      
        entity = restTemplate.getForEntity(uri, User.class);
      
     
    
   

getForObject

getForObject函数实际上是对getForEntity函数的进一步封装，如果你只关注返回的消息体的内容，对其他信息都不关注，此时可以使用getForObject。

示例：

//URL中的{id}占位符最终将会用方法的id参数来填充String url = "http://127.0.0.1:8083/demo/{id}/{userName}?age=18";Long id = 1001L;String userName = "Tom";//方式一：最后一个参数是大小可变的参数列表，每个参数都会按出现顺序插入到指定URL的占位符中User user = restTemplate.getForObject(url, User.class, id, userName);//方式二：将id参数放到Map中，并以id作为key，然后将这个Map作为最后一个参数Map
   
     urlParams = new HashMap<>();urlParams.put("id", id);urlParams.put("userName", userName);User user2 = restTemplate.getForObject(url, User.class, urlParams);//方式二：参考getForEntity案例
   

POST请求

POST请求对应三个方法，postForObject()、postForEntity()和postForLocation()，每个方法同样对应有三个具体的重载方法。postForObject()、postForEntity()类似于getForObject()和postForEntity()，postForLocation()返回的是一个URI对象。

postForEntity

String url = "http://localhost:8080/demo2/{address}";// 方式一User user = new User();user.setAge(25);user.setUsername("王五");// 第4个参数可以是Object... uriVariables 或者 Map
   
     uriVariablesResponseEntity
    
      userResponseEntity = restTemplate.postForEntity(url, user, User.class, "SH");User userBody = userResponseEntity.getBody();HttpStatus statusCode = userResponseEntity.getStatusCode();int statusCodeValue = userResponseEntity.getStatusCodeValue();HttpHeaders headers = userResponseEntity.getHeaders();System.out.println("user = " + userBody + "; statusCode = " + statusCode + "; statusCodeValue = " + statusCodeValue + "; headers = " + headers);
    
   

postForObject

如果你只关注，返回的消息体，可以直接使用postForObject。用法和getForObject一致。

exchange通用请求

String getUrl = "http://127.0.0.1:8083/demo/{id}/{userName}?age=18";//GET资源//参数3是请求头部分；参数4是响应数据要转成对象；最后一个参数用于替换URL中的占位符ResponseEntity
   
     userResponseEntity = restTemplate.exchange(getUrl, HttpMethod.GET, null, User.class, 1001L, "Tom");System.out.println("exchange = " + userResponseEntity + "; response body = " + userResponseEntity.getBody());String postUrl = "http://localhost:8083/demo2";//POST资源HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_JSON);String jsonParams = "{\"username\":\"123\",\"age\":23}";HttpEntity
    
      httpEntity = new HttpEntity(jsonParams, headers);ResponseEntity
     
       responseEntity = restTemplate.exchange(postUrl, HttpMethod.POST, httpEntity, User.class);System.out.println("exchange = " + responseEntity + "; response body = " + responseEntity.getBody());
     
    
   

POST请求，from-data传参

String url = "http://localhost:8083/demo2";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.MULTIPART_FORM_DATA);MultiValueMap map = new LinkedMultiValueMap();map.add("id",1001L);HttpEntity httpEntity = new HttpEntity(map, headers);ResponseEntity
   
     responseEntity = restTemplate.postForEntity(url, httpEntity, User.class);System.out.println(responseEntity.getBody());
   

RestTemplate携带参数和header头信息

String url="http://www.baidu.com";MultiValueMap
   
     map = new LinkedMultiValueMap<>();map.add("id",id);HttpHeaders header = new HttpHeaders();// 需求需要传参为form-data格式header.setContentType(MediaType.MULTIPART_FORM_DATA);HttpEntity
    
     
      > httpEntity = new HttpEntity<>(map, header);JSONObject response = restTemplate.postForObject(url, httpEntity, JSONObject.class);
     
    
   

URI 使用

URI uri = new URIBuilder().setScheme("http").setHost(ip).setPort(port).setPath("/platform/service")            .addParameter("user", "")            .addParameter("service", "")            .build();            UriComponents uriComponents = UriComponentsBuilder.fromUriString(url).build().expand(1001L, "James").encode();URI uri = uriComponents.toUri();

RestTemplate封装

package com.demo.spring;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.http.HttpEntity;import org.springframework.http.HttpHeaders;import org.springframework.http.HttpMethod;import org.springframework.http.ResponseEntity;import org.springframework.stereotype.Component;import org.springframework.util.StringUtils;import org.springframework.web.client.RestTemplate;import sun.misc.BASE64Encoder;import java.io.UnsupportedEncodingException;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import java.util.HashMap;import java.util.Map;@Componentpublic class RestUtil {
       @Autowired    private RestTemplate restTemplate;    //一些自定义的请求头参数    public static final String supplierID = "";    public static final String interfacekey = "";    /**     * DLT专用执行方法     *     * @param param  请求参数：可以添加一些常量请求值     * @param url    访问的url     * @param method 请求的方法     * @return     */    public String execute(Map
   
     param, String url, HttpMethod method) {
           HttpHeaders headers = this.getDefaultHeader();        Map
    
      requestor = this.getDefaultParam();        param.put("requestor", requestor);        param.put("supplierID", supplierID);        HttpEntity
     
    
   

手动指定转换器(HttpMessageConverter)

调用reseful接口传递的数据内容是json格式的字符串，返回的响应也是json格式的字符串。然而restTemplate.postForObject方法的请求参数RequestBean和返回参数ResponseBean却都是java类。是RestTemplate通过HttpMessageConverter自动帮我们做了转换的操作。

默认情况下RestTemplate自动帮我们注册了一组HttpMessageConverter用来处理一些不同的contentType的请求。

• StringHttpMessageConverter来处理text/plain
• MappingJackson2HttpMessageConverter来处理application/json
• MappingJackson2XmlHttpMessageConverter来处理application/xml

可以在org.springframework.http.converter包下找到所有spring帮我们实现好的转换器。

如果现有的转换器不能满足我们的需求，我们还可以实现org.springframework.http.converter.HttpMessageConverter接口自己写一个。

选好一个HttpMessageConverter后并注册到我们的RestTemplate中：

RestTemplate restTemplate = new RestTemplate();//获取RestTemplate默认配置好的所有转换器List
   
    > messageConverters = restTemplate.getMessageConverters();//默认的MappingJackson2HttpMessageConverter在第7个 先把它移除掉messageConverters.remove(6);//添加上GSON的转换器messageConverters.add(6, new GsonHttpMessageConverter());
   

   	
    
     com.google.code.gson
    	
    
     gson
    	
    
     2.8.5
    
   

上面的例子使用GsonHttpMessageConverter替换掉默认用来处理application/json的MappingJackson2HttpMessageConverter。

设置底层连接方式

创建一个RestTemplate的实例，可以像上述例子中简单地调用默认的无参数构造函数。这将使用java.net包中的标准Java类作为底层实现来创建HTTP请求。

但很多时候我们需要像传统的HttpClient那样设置HTTP请求的一些属性。RestTemplate使用了一种很偷懒的方式实现了这个需求，那就是直接使用一个HttpClient作为底层实现。

//生成一个设置了连接超时时间、请求超时时间、异常最大重试次数的httpClientRequestConfig config = RequestConfig.custom()        .setConnectionRequestTimeout(10000)        .setConnectTimeout(10000)        .setSocketTimeout(30000).build();HttpClientBuilder builder = HttpClientBuilder.create()        .setDefaultRequestConfig(config)        .setRetryHandler(new DefaultHttpRequestRetryHandler(5, false));HttpClient httpClient = builder.build();//使用httpClient创建一个ClientHttpRequestFactory的实现ClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);//ClientHttpRequestFactory作为参数构造一个使用作为底层的RestTemplateRestTemplate restTemplate = new RestTemplate(requestFactory);

设置拦截器(ClientHttpRequestInterceptor)

有时候我们需要对请求做一些通用的拦截设置，这就可以使用拦截器进行处理。拦截器需要我们实现org.springframework.http.client.ClientHttpRequestInterceptor接口自己写。

举个简单的例子，写一个在header中根据请求内容和地址添加令牌的拦截器。

import org.springframework.http.HttpRequest;import org.springframework.http.client.ClientHttpRequestExecution;import org.springframework.http.client.ClientHttpRequestInterceptor;import org.springframework.http.client.ClientHttpResponse;import java.io.IOException;public class TokenInterceptor implements ClientHttpRequestInterceptor {
       @Override    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
           //请求地址        String checkTokenUrl = request.getURI().getPath();        //请求内容        String requestBody = new String(body);        //生成令牌        String token = "token";        //将令牌放入请求header中        request.getHeaders().add("X-Auth-Token",token);        request.getHeaders().add("X-Auth-Token","yq");        return execution.execute(request, body);    }}

RestTemplate原理

参考

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