SpringBoot RestTemplate 的使用

一、简介

RestTemplate 在JDK HttpURLConnection、Apache HttpComponents、OkHttp等基础上，封装了更高级别的API，默认依赖JDK HttpURLConnection，连接方式默认长连接。

二、使用

2.1、引入依赖

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

2.2、创建RestTemplate

2.2.1、配置参数

http:
  maxTotal: 100         #最大连接数
  defaultMaxPerRoute: 20  #并发数
  connectTimeout: 1000   #创建连接的最长时间
  connectionRequestTimeout: 500  #从连接池中获取到连接的最长时间
  socketTimeout: 10000 #数据传输的最长时间
  staleConnectionCheckEnabled: true  #提交请求前测试连接是否可用
  validateAfterInactivity: 3000000   #可用空闲连接过期时间,重用空闲连接时会先检查是否空闲时间超过这个时间，如果超过，释放socket重新建立

2.2.2、建立Bean注入 IOC

import org.apache.http.Header;
import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
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.SSLConnectionSocketFactory;
import org.apache.http.impl.client.DefaultConnectionKeepAliveStrategy;
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.message.BasicHeader;
import org.springframework.beans.factory.annotation.Value;
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.http.client.OkHttp3ClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

import java.util.ArrayList;
import java.util.List;

@Configuration
public class RestTemplateConfig {

    @Value("${http.maxTotal}")
    private Integer maxTotal;

    @Value("${http.defaultMaxPerRoute}")
    private Integer defaultMaxPerRoute;

    @Value("${http.connectTimeout}")
    private Integer connectTimeout;

    @Value("${http.connectionRequestTimeout}")
    private Integer connectionRequestTimeout;

    @Value("${http.socketTimeout}")
    private Integer socketTimeout;

    @Value("${http.staleConnectionCheckEnabled}")
    private boolean staleConnectionCheckEnabled;

    @Value("${http.validateAfterInactivity}")
    private Integer validateAfterInactivity;

    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate(httpRequestFactory());
    }

    /**
     * 使用 Apache HttpClient 作为底层客户端
     * 效率: OkHttp > Apache HttpClient > JDK HttpURLConnection
     */
    @Bean
    public ClientHttpRequestFactory httpRequestFactory() {
        return new HttpComponentsClientHttpRequestFactory(httpClient());
    }

    @Bean
    public HttpClient httpClient() {
        Registry<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory>create()
            .register("http", PlainConnectionSocketFactory.getSocketFactory())
            .register("https", SSLConnectionSocketFactory.getSocketFactory())
            .build();
        PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager(registry);
        connectionManager.setMaxTotal(maxTotal); // 最大连接数
        connectionManager.setDefaultMaxPerRoute(defaultMaxPerRoute);    // 单个路由最大连接数
        connectionManager.setValidateAfterInactivity(validateAfterInactivity); // 最大空间时间

        RequestConfig requestConfig = RequestConfig.custom()
            .setSocketTimeout(socketTimeout)        // 服务器返回数据(response)的时间，超过抛出read timeout
            .setConnectTimeout(connectTimeout)      // (握手成功)的时间，超出抛出connect timeout
            .setStaleConnectionCheckEnabled(staleConnectionCheckEnabled) // 提交前检测是否可用
            .setConnectionRequestTimeout(connectionRequestTimeout)// 从连接池中获取连接的超时时间，超时间未拿到可用连接，会抛出org.apache.http.conn.ConnectionPoolTimeoutException: Timeout waiting for connection from pool
            .build();
        // headers
        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"));
        return HttpClientBuilder.create()
            .setDefaultRequestConfig(requestConfig)
            .setConnectionManager(connectionManager)
            .setDefaultHeaders(headers)
            // 保持长连接配置，需要在头添加Keep-Alive
            .setKeepAliveStrategy(new DefaultConnectionKeepAliveStrategy())
            // 重试次数，默认是3次，没有开启
            .setRetryHandler(new DefaultHttpRequestRetryHandler(2, true))
            .build();
    }
}

2.3、API 使用

2.3.1、GET请求

public <T> T getForObject(...)：返回值是HTTP协议的响应体内容。
public <T> ResponseEntity<T> getForEntity(...)：返回的是ResponseEntity，ResponseEntity包含响应体、HTTP状态码、contentType、contentLength、Header等信息。

Map<String,Object> map = new HashMap<>();
map.put("name","aaa");
map.put("age",12);
// 表单提交传参
ResponseEntity<R> responseEntity = restTemplate.getForEntity(url,R.class,map);

2.3.2、POST请求

public URI postForLocation(...)：用POST创建一个新资源，返回UTI对象，可从响应中返回Location报头。
public <T> T postForObject(...)：返回HTTP协议的响应体body内容。
public <T> ResponseEntity<T> postForEntity(...)：返回ResponseEntity，ResponseEntity包含响应体、HTTP状态码、contentType、contentLength、Header等信息。

RestTemplate restTemplate = new RestTemplate();
String url = "http://172.18.20.200:8080/cms/work/queryWorks";
JSONObject jsonObject = new JSONObject();
jsonObject.set("state","01");
jsonObject.set("title","aaaaa");
// Json 传参
ResponseEntity<R> responseEntity = restTemplate.postForEntity(url,jsonObject,R.class);
System.out.println("---ret-getBody: " +responseEntity.getBody());
System.out.println("---ret-getBody-getCode: " +responseEntity.getBody().getCode());
System.out.println("---ret-getBody-getData: " +responseEntity.getBody().getData());

# POST以表单方式提交
//请求地址
String url2 = "......";
//设置请求头, x-www-form-urlencoded格式的数据
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
//提交参数设置
MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
map.add("name","aaaaaa");
//组装请求体
HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(map, httpHeaders);
//发送post请求并打印结果 以String类型接收响应结果JSON字符串
String s = restTemplate.postForObject(url2, request, String.class);
System.out.println(s);

2.3.3、PUT、DELETE请求

PUT请求
一般用来新增或修改资源，没返回值。
	String url = "......";
	User user = new User();
	user.setName("鲁大师");
	restTemplate.put(url,user);

DELETE请求
没返回值,与PUT请求一样。

2.3.4、EXECUTE

RestTemplate restTemplate = new RestTemplate();
//请求地址
String url = "http://172.18.20.200:8080/cms/work/queryWorks";
User user = new User();
user.setName("aaa");
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.setContentType(MediaType.APPLICATION_JSON);
HttpEntity<User> userHttpEntity = new HttpEntity<User>(user, httpHeaders);
ResponseEntity<Object> execute = restTemplate.execute(url, HttpMethod.POST, restTemplate.httpEntityCallback(userHttpEntity), restTemplate.responseEntityExtractor(Object.class));
System.out.println(execute);

2.3.5、上传、下载文件

上传文件
	//需要上传的文件
	String filePath = "/C:/cms/aaa.jpg";
	//请求地址
	String url = "http://localhost:8080/rest/file/test/post/upload";
	// 请求头设置,multipart/form-data格式的数据
	HttpHeaders headers = new HttpHeaders();
	headers.setContentType(MediaType.MULTIPART_FORM_DATA);
	//提交参数设置
	MultiValueMap<String, Object> param = new LinkedMultiValueMap<>();
	param.add("multipartFile", new FileSystemResource(new File(filePath)));
	param.add("userCode", "anightmonarch");
	param.add("userName", "一宿君");
	// 组装请求体
	HttpEntity<MultiValueMap<String, Object>> request = new HttpEntity<>(param, headers);
	//发起请求
	ResponseBean responseBean = restTemplate.postForObject(url, request, ResponseBean.class);
	System.out.println(responseBean);

下载文件
	//需要下载的文件
	String fileName = "121dfga0ab3ba.jpg";
	//用户信息
	String userId = "123456789";
	//请求地址
	String url = "......";
	//提交参数设置
	Map<String,Object> paramMap = new HashMap<String,Object>();
	paramMap.put("fileName",fileName);
	paramMap.put("userId",userId);
	//发起请求（响应内容为字节文件）
	ResponseEntity<byte[]> response = restTemplate.getForEntity(url, byte[].class, paramMap);
	System.out.println("HTTP 响应状态：" + response.getStatusCode());
	//下载文件保存路径
	File savePath = new File("C:\\cms\\download\\img\\");
	if (!savePath.isDirectory()){
		savePath.mkdirs();
	}
	Path path = Paths.get(savePath.getPath() + File.separator + fileName);
	Files.write(path, Objects.requireNonNull(response.getBody(),"下载文件失败！"));