Spring MVC中使用RestTemplate访问REST服务详解
< 返回列表时间: 2018-10-17来源:OSCHINA
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在Java Web开发中,我们通常需要通过GET、POST请求其他系统提供的服务。其中, JDK自带的HttpURLConnection 、 Apache HttpClient 等方式都可以实现。当然,这些方式都有一个很明显的缺陷,那就是代码很繁琐。而Spring提供的RestTemplate封装了这些库的实现,可以让我们的HTTP请求更加简洁、直观。
在RestTemplate中定义了11个独立的操作,它们分别是:
方法 描述
delete() 在特定的URL上对资源执行HTTP DELETE操作
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
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
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资源到特定的URL
headForHeaders() optionsForAllow()
发送HTTP HEAD请求,返回包含特定资源URL的HTTP头 发送HTTP OPTIONS请求,返回对特定URL的Allow头信息

接下来,我将对常用的几个方法分别介绍。
(1)在项目中添加依赖:



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<!-- 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>

<!-- Fastjson -->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.46</version>
</dependency>


(2)在项目中注入RestTemplate:
在注入RestTemplate的bean的时候,可以通过ClientHttpRequestFactory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实现方法:
i)SimpleClientHttpRequestFactory:
也就是底层使用java.net包提供的方式创建Http连接请求。示例代码如下:


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package cn.zifangsky.springbootdemo.config;

import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.ClientHttpRequestFactory;
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.web.client.RestTemplate;

@Configuration
public class RestTemplateConfig {

/**
* 返回RestTemplate
* @param factory
* @return
*/
@Bean
public RestTemplate restTemplate(ClientHttpRequestFactory factory){
//消息转换器,一般情况下可以省略,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接口的第一种实现方式,即:
* SimpleClientHttpRequestFactory:底层使用java.net包提供的方式创建Http连接请求
* @return
*/
@Bean
public SimpleClientHttpRequestFactory simpleClientHttpRequestFactory(){
SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();

requestFactory.setReadTimeout(5000);
requestFactory.setConnectTimeout(5000);

return requestFactory;
}

}



ii)HttpComponentsClientHttpRequestFactory(推荐使用):
也就是底层使用Httpclient连接池的方式创建Http连接请求。示例代码如下:


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package cn.zifangsky.springbootdemo.config;

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;
}

}



(3)使用getForObject()方法发起GET请求:
getForObject()方法实际上是对getForEntity()方法的进一步封装,二者用法类似。 唯一的区别在于getForObject()方法只返回所请求类型的对象, 而getForEntity()方法会返回请求的对象以及响应的Header、响应状态码等额外信息。
三个getForObject()方法的签名如下:


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<T> T getForObject(String url, Class<T> responseType, Object... uriVariables) throws RestClientException;

<T> T getForObject(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;

<T> T getForObject(URI url, Class<T> responseType) throws RestClientException;

示例代码如下:


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package cn.zifangsky.SpringBootDemo.controller;

import java.util.HashMap;
import java.util.Map;

import org.junit.Test;
import org.junit.runner.RunWith;
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.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.web.WebAppConfiguration;
import org.springframework.web.client.RestTemplate;

import cn.zifangsky.springbootdemo.config.RestTemplateConfig;
import cn.zifangsky.springbootdemo.config.WebMvcConfig;
import cn.zifangsky.springbootdemo.model.DemoObj;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes={WebMvcConfig.class,RestTemplateConfig.class})
@WebAppConfiguration("src/main/resources")
public class TestRestTemplate {

@Autowired
private RestTemplate restTemplate;

/**
* 测试最基本的Get请求
*/
@Test
public void testGetMethod1(){
DemoObj obj = restTemplate.getForObject("http://127.0.0.1:9090/rest/testJson2?id={1}&name={2}"
, DemoObj.class
, 1,"Tom");

System.out.println(obj);
}

}

注:本篇文章的单元测试请求的REST服务均来源于上一篇文章: https://www.zifangsky.cn/1215.html
上面代码设置请求参数使用了数字占位符,同时getForObject()方法的最后一个参数是一个可变长度的参数,用于一一替换前面的占位符。当然,除了这种方式之外,还可以使用Map来设置参数,比如:


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/**
* 测试Get请求另一种设置参数的方式
*/
@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);
}

运行单元测试之后,最后输出如下: DemoObj [id=2, name=Tom Ret]
此外需要注意的是,由于上面代码只是简单的单元测试,因此请求URL就直接硬编码在代码中了。实际开发则需要将之配置到配置文件或者Zookeeper、Redis中。比如这样:


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package cn.zifangsky.springbootdemo.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import cn.zifangsky.springbootdemo.model.DemoObj;

@RestController
@RequestMapping("/restTemplate")
public class RestTemplateController {

@Value("${SERVER_URL}")
private String SERVER_URL;

@Autowired
private RestTemplate restTemplate;

@RequestMapping(path="/getDemoObj",produces={MediaType.APPLICATION_JSON_UTF8_VALUE})
public DemoObj getDemoObj(){
DemoObj obj = restTemplate.getForObject(SERVER_URL + "/rest/testXML?id={1}&name={2}"
, DemoObj.class
, 1,"Tom");

return obj;
}

}



(4)使用getForEntity()方法发起GET请求:
三个getForEntity()方法的签名如下:


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<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;

示例代码如下:


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/**
* 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(){
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);
}

运行单元测试之后,最后输出如下: 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]}
(5)使用postForObject()方法发起POST请求:
在RestTemplate中,POST请求跟GET请求类似,也可以使用如下三个方法来请求:


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<T> T postForObject(String url, Object request, Class<T> responseType, Object... uriVariables)
throws RestClientException;

<T> T postForObject(String url, Object request, Class<T> responseType, Map<String, ?> uriVariables)
throws RestClientException;

<T> T postForObject(URI url, Object request, Class<T> responseType) throws RestClientException;

示例代码如下:


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/**
* 测试最基本的Post请求
*/
@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);
}

运行单元测试之后,最后输出如下: DemoObj [id=2, name=Tim Ret]
(6)使用postForEntity()方法发起POST请求:
三个postForEntity()方法的签名如下:


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<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;

示例代码如下:


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/**
* 测试Post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 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);
}

运行单元测试之后,最后输出如下: 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]}
(7)使用exchange()方法执行指定的HTTP请求:
exchange()方法跟上面的getForObject()、getForEntity()、postForObject()、postForEntity()等方法不同之处在于它可以指定请求的HTTP类型。示例代码如下:


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/**
* 测试Exchange请求
*/
@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());
}

运行单元测试之后,最后输出如下: responseEntity.getBody():{“id”:2,”name”:”Converter Ret”}
responseEntity.getHeaders():{Date=[Fri, 09 Feb 2018 06:42:29 GMT], Content-Type=[application/x-zifangsky], Transfer-Encoding=[chunked]}
参考: https://segmentfault.com/a/1190000011093597 http://rensanning.iteye.com/blog/2362105
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