Spring restTemplate

什么是RestTemplate

RestTemplate是Spring提供的用于访问Rest服务的客户端，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。

 

项目中注入RestTemplate

首先在项目中添加依赖：

<!-- Jackson对自动解析JSON和XML格式的支持 -->
<dependency>
    <groupId>com.fasterxml.jackson.jaxrs</groupId>
    <artifactId>jackson-jaxrs-json-provider</artifactId>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-xml</artifactId>
</dependency>
 
<!-- HttpClient -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
</dependency>

在注入RestTemplate的bean的时候，可以通过ClientHtppRequestFactory指定RestTemplate发起HTTP请求的底层实现所采用的类库。对此，ClientHttpRequestFactory接口主要提供了以下两种方法： 
一种是SimpleClientHttpRequestFactory，使用J2SE提供的方式(即java.net包提供的方式)创建底层的HTTP请求连接。 
另一种是使用HttpComponentsClientHttpRequestFactory方式，底层使用HttpClient访问远程的http服务，使用HttpClient可以配置连接池和证书等信息。 
以下的两个方法都采用线程安全的单例(懒汉模式) 
(1)SimpleClientHttpRequestFactory

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Lazy;
import org.springframework.http.client.SimpleClientHttpRequestFactory;
import org.springframework.http.converter.FormHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
import org.springframework.stereotype.Component;
import org.springframework.web.client.DefaultResponseErrorHandler;
import org.springframework.web.client.RestTemplate;

import javax.annotation.PostConstruct;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;

@Component
@Lazy(false)
public class SimpleRestClient {

    private static final Logger LOGGER = LoggerFactory.getLogger(SimpleRestClient.class);

    private static RestTemplate restTemplate;

    static {
        SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
        requestFactory.setReadTimeout(5000);
        requestFactory.setConnectTimeout(5000);

        // 添加转换器
        List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
        messageConverters.add(new StringHttpMessageConverter(Charset.forName("UTF-8")));
        messageConverters.add(new FormHttpMessageConverter());
        messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
        messageConverters.add(new MappingJackson2HttpMessageConverter());

        restTemplate = new RestTemplate(messageConverters);
        restTemplate.setRequestFactory(requestFactory);
        restTemplate.setErrorHandler(new DefaultResponseErrorHandler());

        LOGGER.info("SimpleRestClient初始化完成");
    }

    private SimpleRestClient() {

    }

    @PostConstruct
    public static RestTemplate getClient() {
        return restTemplate;
    }

}

(2）HttpComponentsClientHttpRequestFactory（推荐使用）

import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
 
import org.apache.http.Header;
import org.apache.http.client.HttpClient;
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.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.converter.FormHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
import org.springframework.web.client.RestTemplate;
 
@Configuration
public class RestTemplateConfig {
 
    /**
     * 返回RestTemplate
     * @param factory
     * @return
     */
    @Bean
    public RestTemplate restTemplate(ClientHttpRequestFactory factory){
        //消息转换器，Spring Boot环境可省略，只需要添加相关依赖即可
//        List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
//        messageConverters.add(new StringHttpMessageConverter(Charset.forName("UTF-8")));
//        messageConverters.add(new FormHttpMessageConverter());
//        messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
//        messageConverters.add(new MappingJackson2HttpMessageConverter());
        
        RestTemplate restTemplate = new RestTemplate(factory);
//        restTemplate.setMessageConverters(messageConverters);
        
        return restTemplate;
    }
    
    /**
     * ClientHttpRequestFactory接口的另一种实现方式（推荐使用），即：
     * HttpComponentsClientHttpRequestFactory：底层使用Httpclient连接池的方式创建Http连接请求
     * @return
     */
    @Bean
    public HttpComponentsClientHttpRequestFactory httpComponentsClientHttpRequestFactory(){
        //Httpclient连接池，长连接保持30秒
        PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager(30, TimeUnit.SECONDS);
        
        //设置总连接数
        connectionManager.setMaxTotal(1000);
        //设置同路由的并发数
        connectionManager.setDefaultMaxPerRoute(1000);
        
        //设置header
        List<Header> headers = new ArrayList<Header>();
        headers.add(new BasicHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.3; rv:36.0) Gecko/20100101 Firefox/36.04"));
        headers.add(new BasicHeader("Accept-Encoding", "gzip, deflate"));
        headers.add(new BasicHeader("Accept-Language", "zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3"));
        headers.add(new BasicHeader("Connection", "keep-alive"));
        
        //创建HttpClient
        HttpClient httpClient = HttpClientBuilder.create()
                .setConnectionManager(connectionManager)
                .setDefaultHeaders(headers)
                .setRetryHandler(new DefaultHttpRequestRetryHandler(3, true)) //设置重试次数
                .setKeepAliveStrategy(new DefaultConnectionKeepAliveStrategy()) //设置保持长连接
                .build();
        
        //创建HttpComponentsClientHttpRequestFactory实例
        HttpComponentsClientHttpRequestFactory requestFactory = 
                new HttpComponentsClientHttpRequestFactory(httpClient);
        
        //设置客户端和服务端建立连接的超时时间
        requestFactory.setConnectTimeout(5000);
        //设置客户端从服务端读取数据的超时时间
        requestFactory.setReadTimeout(5000);
        //设置从连接池获取连接的超时时间，不宜过长
        requestFactory.setConnectionRequestTimeout(200);
        //缓冲请求数据，默认为true。通过POST或者PUT大量发送数据时，建议将此更改为false，以免耗尽内存
        requestFactory.setBufferRequestBody(false);
        
        return requestFactory;
    }
    
}

RestTemplate提供了很多方法，可以与HTTP方法对应。

HTTP方法	RestTemplate方法	说明
DELETE	delete()	在特定的URL上对资源执行HTTP DELETE操作
GET	getForEntity() getForObject()	getForEntity():发送一个HTTP GET请求，返回的ResponseEntity包含了响应体所映射成的对象。  getForObject():发送一个HTTP GET请求，返回根据响应体映射形成的对象
POST	postForEntity() postForLocation() postForObject()	postForEntity(): POST数据到一个URL，返回的ResponseEntity包含了响应体所映射成的对象。  postForLocation(): POST数据到一个URL，返回新创建资源的URL。 postForObject(): POST数据到一个URL，返回根据响应体映射形成的对象
PUT	put()	PUT资源到特定的URL
HEAD	headForHeaders()	发送HTTP HEAD请求，返回包含特定资源URL的HTTP头
OPTIONS	optionsForAllow()	发送HTTP OPTIONS请求，返回对特定URL的Allow头信息
PATCH and others	exchange() execute()	exchange(): 在URL上执行特定的HTTP方法，返回的ResponseEntity包含了响应体所映射成的对象  execute():在URL上执行特定的HTTP方法，返回一个从响应体映射得到的对象

接下来讲一下RestTemplate的这几个方法如何使用。 

GET请求方式的两种方法 
1. getForEntity() 
三个getForEntity()方法的签名：

<T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... uriVariables) throws RestClientException;
 
<T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;
 
<T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType) throws RestClientException;

示例代码：

    /**
     * 测试Get请求返回详细信息，包括：响应正文、响应状态码、响应Header等
     */
    @Test
    public void testGetMethod3(){
        //第一个参数为要调用的服务的地址，第二个参数为返回值的类型，第三和第四个参数时url中的传参
        ResponseEntity<DemoObj> responseEntity = restTemplate.getForEntity("http://127.0.0.1:9090/rest/testJson2?id={1}&name={2}"
                , DemoObj.class
                , 1,"Tom");
        
        DemoObj body = responseEntity.getBody();
        int statusCodeValue = responseEntity.getStatusCodeValue();
        HttpHeaders headers = responseEntity.getHeaders();
        
        System.out.println("responseEntity.getBody()：" + body);
        System.out.println("responseEntity.getStatusCodeValue()：" + statusCodeValue);
        System.out.println("responseEntity.getHeaders()：" + headers);
    }

结果：

responseEntity.getBody()：DemoObj [id=2, name=Tom Ret]
responseEntity.getStatusCodeValue()：200
responseEntity.getHeaders()：{Date=[Fri, 09 Feb 2018 06:22:28 GMT], Content-Type=[application/json;charset=utf-8], Transfer-Encoding=[chunked]}

再来看一个Map传参的例子：

@RequestMapping("/sayhello2")
public String sayHello2() {
    Map<String, String> map = new HashMap<>();
    map.put("name", "李四");
    ResponseEntity<String> responseEntity = restTemplate.getForEntity("http://HELLO-SERVICE/sayhello?name={name}", String.class, map);
    return responseEntity.getBody();
}

当然，第一个参数也可以是URI而不是字符串，可以通过Spring中的UriComponents来构建uri即可。

@RequestMapping("/sayhello3")
public String sayHello3() {
    UriComponents uriComponents = UriComponentsBuilder.fromUriString("http://HELLO-SERVICE/sayhello?name={name}").build().expand("王五").encode();
    URI uri = uriComponents.toUri();
    ResponseEntity<String> responseEntity = restTemplate.getForEntity(uri, String.class);
    return responseEntity.getBody();
}

2.getForObject() 
getForObject()实际上是对getForEntity()的进一步封装，用法类似，唯一的区别就是getForObject()方法只返回请求类型的对象，而getForEntity()会返回请求的对象以及响应的Header，响应状态码等额外信息。

@RequestMapping("/book2")
public Book book2() {
    Book book = restTemplate.getForObject("http://HELLO-SERVICE/getbook1", Book.class);
    return book;
}

    @Test
    public void testGetMethod2(){
        Map<String, String> uriVariables = new HashMap<String, String>();
        uriVariables.put("var_id", "1");
        uriVariables.put("var_name", "Tom");
        
        DemoObj obj = restTemplate.getForObject("http://127.0.0.1:9090/rest/testJson2?id={var_id}&name={var_name}"
                , DemoObj.class
                , uriVariables);
        
        System.out.println(obj);
    }

POST请求的三种方法 
1. postForEntity() 
POST请求和GET请求类似，也是三种方法：

<T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Object... uriVariables)
            throws RestClientException;
 
<T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Map<String, ?> uriVariables)
            throws RestClientException;
 
<T> ResponseEntity<T> postForEntity(URI url, Object request, Class<T> responseType) throws RestClientException;

看个示例：

    @Test
    public void testPostMethod2(){
        DemoObj request = new DemoObj(1l, "Tim");
        
        ResponseEntity<DemoObj> responseEntity = restTemplate.postForEntity("http://127.0.0.1:9090/rest/testJson1"
                , request, DemoObj.class);
        
        DemoObj body = responseEntity.getBody();
        int statusCodeValue = responseEntity.getStatusCodeValue();
        HttpHeaders headers = responseEntity.getHeaders();
        
        System.out.println("responseEntity.getBody()：" + body);
        System.out.println("responseEntity.getStatusCodeValue()：" + statusCodeValue);
        System.out.println("responseEntity.getHeaders()：" + headers);
    }

结果：

responseEntity.getBody()：DemoObj [id=2, name=Tim Ret]
responseEntity.getStatusCodeValue()：200
responseEntity.getHeaders()：{Date=[Fri, 09 Feb 2018 06:32:02 GMT], Content-Type=[application/json;charset=utf-8], Transfer-Encoding=[chunked]}

2.postForObject()

    @Test
    public void testPostMethod1(){
        DemoObj request = new DemoObj(1l, "Tim");
        
        DemoObj obj = restTemplate.postForObject("http://127.0.0.1:9090/rest/testJson1"
                , request, DemoObj.class);
        
        System.out.println(obj);
    }

3.postForLocation()
postForLocation()也是提交新资源，提交成功之后，返回新资源的URI，postForLocation的参数和前面两种的参数基本一致，只不过该方法的返回值为Uri，这个只需要服务提供者返回一个Uri即可，该Uri表示新资源的位置。

PUT请求 
在RestTemplate中，PUT请求可以通过put方法调用，put方法的参数和前面介绍的postForEntity方法的参数基本一致，只是put方法没有返回值而已。

@RequestMapping("/put")
public void put() {
    Book book = new Book();
    book.setName("红楼梦");
    restTemplate.put("http://HELLO-SERVICE/getbook3/{1}", book, 99);
}

DELETE请求

@RequestMapping("/delete")
public void delete() {
    restTemplate.delete("http://HELLO-SERVICE/getbook4/{1}", 100);
}

exchange()方法执行指定的HTTP请求 
exchange()方法同上面的很多方法不同的是，它可以指定请求的HTTP方式。

    @Test
    public void testExchange(){
        //设置header
        HttpHeaders headers = new HttpHeaders();
        headers.add("Content-Type", "application/x-zifangsky");
        
        //设置参数
        String requestBody = "1#Converter";
        HttpEntity<String> requestEntity = new HttpEntity<String>(requestBody,headers);
 
        ResponseEntity<String> responseEntity = restTemplate.exchange("http://127.0.0.1:9090/convert"
                , HttpMethod.POST, requestEntity, String.class);
        
        System.out.println("responseEntity.getBody()：" + responseEntity.getBody());
        System.out.println("responseEntity.getHeaders()：" + responseEntity.getHeaders());
    }

手动指定转换器 
调用restful接口传递的数据是json格式的字符串，返回的响应也是json格式的字符串。