Spring Cloud系列（七）RestTemplate详解

在系列四中讲解Ribbon时使用了RestTemplate对象。该对象会使用Ribbon的自动化配置，并同时配置@LoadBalanced还能够开启客户端负载均衡。下面介绍一下RestTemplate针对不同请求类型和参数类型的使用。

GET请求

在RestTemplate中对GET请求可以通过如下两种方式实现。

第一种，getForEntity函数。该方法返回的是ResponseEntity，该对象是Spring对Http请求响应的封装。其中主要存储了HTTP的几个重要元素，比如HTTP请求状态码的枚举对象HttpStatus（我们常说的404,500）、在他的父类HttpEntity中还存储着HTTP请求的头信息对象HttpHeaders以及泛型类型的请求体对象(响应码、contentType、contentLength、响应消息体等)。

常用方式

ResponseEntity<String> responseEntity = restTemplate.getForEntity("http://HELLO-SERVICE/user1?name={1}", String.class,"xiaoming");
String body = responseEntity.getBody();

//返回对象格式
ResponseEntity<User> responseEntity = restTemplate.getForEntity("http://HELLO-SERVICE/user2?name={1}&age={2}", User.class,"xiaoming",22);
User user = responseEntity.getBody();

getForEntity函数提供了三种重载方法

1.getForEntity(String url,Class responseType,Object...urlVariables)

该方法提供了三个参数，第一个参数url为请求的地址，第二个参数responseType是请求响应体body的包装类型，urlVariables为url中的参数绑定。get请求参数可以拼接到url后面，例如：http:ip//xxx/xx?username=xxx，但是更好的方式是使用占位符并配合urlVariables参数实现get请求参数的绑定。注意因为urlVariables是一个数组，所以它的顺序会对应url值占位符的数字顺序。当然你也可以使用json字符串的形式：

ResponseEntity<User> responseEntity = restTemplate.getForEntity("http://HELLO-SERVICE/user3?jsonStr={jsonStr}", User.class,"{\"name\":\"xiaoming\",\"age\":\"22\"}");
User user = responseEntity.getBody();

2.getForEntity(String url,Class responseType,Map urlVariables)

这里urlVariables参数类型是Map，所以在使用该方法进行参数绑定时必须在占位符中指定Map中参数的key值。

Map<String,Object> params = new HashMap<String,Object>();
params.put("name", "xiaoming");
params.put("age", 22);
ResponseEntity<User> responseEntity = restTemplate.getForEntity("http://HELLO-SERVICE/user2?name={name}&age={age}", User.class,params);
User user = responseEntity.getBody();

3.getForEntity(URI uri,Class responseType)

该方法使用URI对象来替代之前的url和urlVariables参数来指定访问地址和参数绑定。URI是JDK java.net包下的类，他表示一个统一资源标识符引用。

UriComponents uriComponents = UriComponentsBuilder.fromUriString("http://HELLO-SERVICE/user1?name={name}").build().expand("xiaoming").encode();
URI uri = uriComponents.toUri();
ResponseEntity<String> responseEntity = restTemplate.getForEntity(uri, String.class);
String body = responseEntity.getBody();

第二种，getForObject函数，该方法可以理解为getForEntity函数的进一步封装。它通过HttpMessageConverterExtractor对HTTP的请求响应体body内容进行对象转换，实现请求直接返回包装好的对象内容,该函数少了一步获取body的步骤所以更方便。比如：

String result = restTemplate.getForObject("http://HELLO-SERVICE/user1?name={1}",String.class,"xiaoming");

//返回对象格式
User user = restTemplate.getForObject("http://HELLO-SERVICE/user2?name={1}&age={2}", User.class, "xiaoming",22);

getForObject函数也提供了三种重载方法，参数类似于上面介绍的三个。

1.getForObject(String url,Class responseType,Object...urlVariables)

2.getForObject(String url,Class responseType,Map urlVariables)

3.getForObject(URI uri,Class responseType)

POST请求

在RestTemplate中，对POST请求可以通过如下三个方法进行调用实现。

第一种：postForEntity函数。该方法同GET请求中的getForEntity类似，会在调用后返回ResponseEntity<T>对象，其中T为请求响应的body类型。比如：

User user = new User("xiaoming",22);
ResponseEntity<String> responseEntity = restTemplate.postForEntity("http://HELLO-SERVICE/user4", user, String.class);
String body = responseEntity.getBody();

postForEntity函数也实现了三种重载方法

1.postForEntity(String url,Object request,Class responseType,Object...urlVariables)

2.postForEntity(String url,Object request,Class responseType,Map urlVariables)

3.postForEntity(URI uri,Object request,Class responseType)

这些函数中的参数方法大部分与getForEntity一致，需要注意的是新加的request参数，该参数可以是一个普通对象，也可以是一个HttpEntity对象。如果是一个普通对象，而非HttpEntity对象的时候，RestTemplate会将请求对象转换为一个HttpEntity对象来处理，其中Object就是request的类型，request内容会被视作完整的body来处理；而如果request是一个HttpEntity对象，那么就会被当作一个完整的HTTP请求对象来处理，这个request中不仅包含了body的内容也包含了header的内容。

HttpHeaders headers = new HttpHeaders();
headers.add("token", "xxxxxxxxxxx");
HttpEntity httpEntity = new HttpEntity(headers);
headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
MultiValueMap<String, String> map= new LinkedMultiValueMap<String, String>();
map.add("age", "33");
HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<MultiValueMap<String, String>>(map, headers);
ResponseEntity<User> responseEntity = restTemplate.postForEntity("http://HELLO-SERVICE/user5", request, User.class);
String body = responseEntity.getBody().toString();

第二种，postForObject函数。该方法和getForObject类似，它的作用是简化postForEntity的后续处理。通过直接将请求响应的body内容包装成对象来使用。

User user = new User("xiaoming",22);
String body = restTemplate.postForObject("http://HELLO-SERVICE/user4", user, String.class);

postForObject函数也实现了三种重载方法，可以参考get请求的getForObject

1.postForObject(String url,Object request,Class responseType,Object...urlVariables)

2.postForObject(String url,Object request,Class responseType,Map urlVariables)

3.postForObject(URI uri,Object request,Class responseType)

第三种，postForLocation函数。该方法实现了以POST请求提交资源，并返回新资源的URI。

User user = new User("xiaoming",22);
URI uri = restTemplate.postForLocation("http://HELLO-SERVICE/user", user);

postForLocation函数也实现了三种重载方法，可以参考get请求的getForObject

1.postForLocation(String url,Object request,Object...urlVariables)

2.postForLocation(String url,Object request,Map urlVariables)

3.postForLocation(URI uri,Object request)

由于postForLocation函数会返回新资源的URI，该URI就相当于指定返回类型，所以此方法实现的POST请求不需要像postForEntity和postForObject那样指定responseType。

PUT请求

int id = 1;
User user = new User("xiaoming",22);
restTemplate.put("http://HELLO-SERVICE/user6/{1}", user, id);

put函数也实现了三种重载方法

1.put(String url,Object request,Object...urlVariables)

2.put(String url,Object request,Map urlVariables)

3.put(URI uri,Object request)

put方法返回类型为void，所以没有返回值。

DELETE请求

int id = 1;
restTemplate.delete("http://HELLO-SERVICE/user7/{1}",id);

delete函数也实现了三种重载方法

1.delete(String url,Object...urlVariables)

2.delete(String url,Map urlVariables)

3.delete(URI uri)

由于我们进行REST请求时，通常将DELETE请求的唯一标识拼接在url中，所以DELETE请求也不需要request的body信息。

exchange()函数

当然也可以用统一的模板进行四中方式的请求

restTemplate.exchange(
        String url, 
        HttpMethod method,
        HttpEntity requestEntity, 
        Class responseType, 
        Object uriVariables[]
    )

1）url: 请求地址；
2）method: 请求类型(如：POST,PUT,DELETE,GET)；
3）requestEntity: 请求实体，封装请求头，请求内容
4）responseType: 响应类型，根据服务接口的返回类型决定
5）uriVariables: url中参数变量值

POST请求

String params= "{\"name\":\"小明\",\"age\":33}";
HttpHeaders headers = new HttpHeaders(); 
MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8");
headers.setContentType(type);
HttpEntity<String> entity = new HttpEntity<String>(params,headers);
ResponseEntity<User> resp = restTemplate.exchange("http://HELLO-SERVICE/user9", HttpMethod.POST, entity, User.class);

PUT请求

String params= "{\"name\":\"小明\",\"age\":33}";
HttpHeaders headers = new HttpHeaders(); 
//乱码
MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8");
headers.setContentType(type);
HttpEntity<String> entity = new HttpEntity<String>(params,headers);
ResponseEntity<String> resp = restTemplate.exchange("http://HELLO-SERVICE/user10", HttpMethod.PUT, entity, String.class);

DELETE请求


ResponseEntity<String> resp = restTemplate.exchange("http://HELLO-SERVICE/user11/{1}", HttpMethod.DELETE, null, String.class,1);

GET请求

ResponseEntity<User> resp = restTemplate.exchange("http://HELLO-SERVICE/user8?jsonStr={jsonStr}", HttpMethod.GET, null, User.class,"{\"name\":\"xiaoming\",\"age\":33}");

如果返回复杂的数据比如数组或list需要用下面的方式

StringBuilder sb = new StringBuilder();
ResponseEntity<User[]> resp = restTemplate.exchange("http://HELLO-SERVICE/user12?jsonStr={jsonStr}", HttpMethod.GET, null, User[].class,"{\"name\":\"xiaoming\",\"age\":33}");
for(User user : resp.getBody()){
	sb.append(user.toString()+"<br>");
}

StringBuilder sb = new StringBuilder();
ParameterizedTypeReference<List<User>> res = new ParameterizedTypeReference<List<User>>(){};
ResponseEntity<List<User>> resp = restTemplate.exchange("http://HELLO-SERVICE/user13?jsonStr={jsonStr}", HttpMethod.GET, null, res,"{\"name\":\"xiaoming\",\"age\":33}");
for(User user : resp.getBody()){
	sb.append(user.toString()+"<br>");
}

对于返回属性中有范型数据的复合对象，比如分页对象

ResponseEntity<String> results = restTemplate.exchange(url,HttpMethod.GET, null, String.class, params);
// 借助com.fasterxml.jackson.databind.ObjectMapper 对象来解析嵌套的json字符串    
ObjectMapper mapper = new ObjectMapper(); mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
PageInfo<Product> page = mapper.readValue(results.getBody(), new TypeReference<PageInfo<Product>>() { });

最后附上代码

消费者代码

package com.wya.springboot.controller;


import java.util.Map;

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.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@RestController
public class RestTemplateController {

	@Autowired
	private RestTemplate restTemplate;
	
	@GetMapping("restTemplate1")
	public String rest1(){
		ResponseEntity<String> responseEntity = 
				restTemplate.getForEntity("http://HELLO-SERVICE/user1?name={1}", String.class,"xiaoming");
		String body = responseEntity.getBody();
		return body;
	}
	
	@GetMapping("restTemplate2")
	public String rest2(){
		ResponseEntity<User> responseEntity = 
				restTemplate.getForEntity("http://HELLO-SERVICE/user2?name={1}&age={2}", User.class,"xiaoming",22);
		User user = responseEntity.getBody();
		return user.toString();
	}
	
	@GetMapping("restTemplate3")
	public String rest3(){
		ResponseEntity<User> responseEntity = 
				restTemplate.getForEntity("http://HELLO-SERVICE/user3?jsonStr={jsonStr}", User.class,"{\"name\":\"xiaoming\",\"age\":22}");
		User user = responseEntity.getBody();
		return user.toString();
	}
	
	@GetMapping("restTemplate4")
	public String rest4(){
		String result = restTemplate.getForObject("http://HELLO-SERVICE/user1?name={1}",String.class,"xiaoming");
		return result;
	}

	@GetMapping("restTemplate5")
	public String rest5(){
		User user = restTemplate.getForObject("http://HELLO-SERVICE/user2?name={1}&age={2}", User.class, "xiaoming",22);
		return user.toString();
	}
	
	@GetMapping("restTemplate6")
	public String rest6(){
		User user = new User("xiaoming",22);
		ResponseEntity<String> responseEntity = restTemplate.postForEntity("http://HELLO-SERVICE/user4", user, String.class);
		return responseEntity.getBody();
	}
	
	@GetMapping("restTemplate7")
	public String rest7(){
		HttpHeaders headers = new HttpHeaders();
		headers.add("token", "xxxxxxxxxxx");
		HttpEntity httpEntity = new HttpEntity(headers);
		headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
		MultiValueMap<String, String> map= new LinkedMultiValueMap<String, String>();
		map.add("age", "33");
		HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<MultiValueMap<String, String>>(map, headers);
		ResponseEntity<User> responseEntity = restTemplate.postForEntity("http://HELLO-SERVICE/user5", request, User.class);
		String body = responseEntity.getBody().toString();
		return body;
	}
	
	@GetMapping("restTemplate8")
	public String rest8(){
		User user = new User("xiaoming",22);
		String body = restTemplate.postForObject("http://HELLO-SERVICE/user4", user, String.class);
		return body;
	}
	
	@GetMapping("restTemplate9")
	public String rest9(){
		int id = 1;
		User user = new User("xiaoming",22);
		restTemplate.put("http://HELLO-SERVICE/user6/{1}", user, id);
		return "success";
	}
	
	@GetMapping("restTemplate10")
	public String rest10(){
		int id = 1;
		restTemplate.delete("http://HELLO-SERVICE/user7/{1}",id);
		return "success";
	}
	
	@GetMapping("restTemplate11")
	public String rest11(){
		ResponseEntity<User> resp = restTemplate.exchange("http://HELLO-SERVICE/user8?jsonStr={jsonStr}", HttpMethod.GET, null, User.class,"{\"name\":\"xiaoming\",\"age\":33}");
		return resp.getBody().toString();
	}
	
	@GetMapping("restTemplate12")
	public String rest12(){
		String params= "{\"name\":\"小明\",\"age\":33}";
		HttpHeaders headers = new HttpHeaders(); 
		MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8");
        headers.setContentType(type);
		HttpEntity<String> entity = new HttpEntity<String>(params,headers);
		ResponseEntity<User> resp = restTemplate.exchange("http://HELLO-SERVICE/user9", HttpMethod.POST, entity, User.class);
		return resp.getBody().toString();
	}
	
	@GetMapping("restTemplate13")
	public String rest13(){
		String params= "{\"name\":\"小明\",\"age\":33}";
		HttpHeaders headers = new HttpHeaders(); 
		MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8");
        headers.setContentType(type);
		HttpEntity<String> entity = new HttpEntity<String>(params,headers);
		ResponseEntity<String> resp = restTemplate.exchange("http://HELLO-SERVICE/user10", HttpMethod.PUT, entity, String.class);
		return resp.getBody();
	}
	
	@GetMapping("restTemplate14")
	public String rest14(){
		ResponseEntity<String> resp = restTemplate.exchange("http://HELLO-SERVICE/user11/{1}", HttpMethod.DELETE, null, String.class,1);
		return resp.getBody();
	}

@GetMapping("restTemplate15")
	public String rest15(){
		StringBuilder sb = new StringBuilder();
		ResponseEntity<User[]> resp = restTemplate.exchange("http://HELLO-SERVICE/user12?jsonStr={jsonStr}", HttpMethod.GET, null, User[].class,"{\"name\":\"xiaoming\",\"age\":33}");
		for(User user : resp.getBody()){
			sb.append(user.toString()+"<br>");
		}
		return sb.toString();
	}
	
	@GetMapping("restTemplate16")
	public String rest16(){
		StringBuilder sb = new StringBuilder();
		ParameterizedTypeReference<List<User>> res = new ParameterizedTypeReference<List<User>>(){};
		ResponseEntity<List<User>> resp = restTemplate.exchange("http://HELLO-SERVICE/user13?jsonStr={jsonStr}", HttpMethod.GET, null, res,"{\"name\":\"xiaoming\",\"age\":33}");
		for(User user : resp.getBody()){
			sb.append(user.toString()+"<br>");
		}
		return sb.toString();
	}
	
}

服务提供者代码

package com.wya.springboot.controller;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URLDecoder;

import javax.servlet.http.HttpServletRequest;

import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import com.alibaba.fastjson.JSONObject;


@RestController
public class UserController {
	
	
	@GetMapping("user1")
	public String user1(String name){
		return name+",21";
	}
	
	@GetMapping("user2")
	public User user2(String name,int age){
		return new User(name, age);
	}
	
	@GetMapping("user3")
	public User user3(String jsonStr){
		JSONObject user = JSONObject.parseObject(jsonStr);
		String name = user.getString("name");
		int age = user.getIntValue("age");
		return new User(name, age);
	}
	
	@PostMapping("user4")
	public String user4(@RequestBody User user){
		return user.toString();
	}
	
	@PostMapping("user5")
	public User user5(int age,HttpServletRequest request){
		String token = request.getHeader("token");
		return new User(token,age);
	}
	
	@PutMapping("user6/{id}")
	public String user6(@PathVariable("id") int id,@RequestBody User user){
		System.out.println(id+","+user.toString());
		return user.toString();
	}
	
	@DeleteMapping("user7/{id}")
	public void user7(@PathVariable("id") int id){
		System.out.println(id);
	}
	
	@GetMapping("user8")
	public User user8(String jsonStr){
		JSONObject user = JSONObject.parseObject(jsonStr);
		String name = user.getString("name");
		int age = user.getIntValue("age");
		return new User(name, age);
	}
	
	@PostMapping("user9")
	public User user9(HttpServletRequest request){
		String jsonStr = getBody(request);
		JSONObject user = JSONObject.parseObject(jsonStr);
		String name = user.getString("name");
		int age = user.getIntValue("age");
		return new User(name, age);
	}
	
	@PutMapping("user10")
	public User user10(HttpServletRequest request){
		String jsonStr = getBody(request);
		JSONObject user = JSONObject.parseObject(jsonStr);
		String name = user.getString("name");
		int age = user.getIntValue("age");
		return new User(name, age);
	}
	
	@DeleteMapping("user11/{id}")
	public String user11(@PathVariable("id") int id){
		System.out.println(id);
		return "success";
	}

    @GetMapping("user12")
	public User[] user12(String jsonStr){
		JSONObject user = JSONObject.parseObject(jsonStr);
		String name = user.getString("name");
		int age = user.getIntValue("age");
		User[] users = {new User(name,age),new User(name, age)};
		return users;
	}
	
	@GetMapping("user13")
	public List<User> user13(String jsonStr){
		JSONObject user = JSONObject.parseObject(jsonStr);
		String name = user.getString("name");
		int age = user.getIntValue("age");
		List<User> users = new ArrayList<User>();
		users.add(new User(name,age));
		users.add(new User(name,age));
		return users;
	}
	
	private String getBody(HttpServletRequest request){
		BufferedReader br = null;
        StringBuilder sb = new StringBuilder("");
        try
        {
            br = request.getReader();
            String str;
            while ((str = br.readLine()) != null)
            {
                sb.append(str);
            }
            br.close();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (null != br)
            {
                try
                {
                    br.close();
                }
                catch (IOException e)
                {
                    e.printStackTrace();
                }
            }
        }
        return sb.toString();
	}
}

注意：消费者和服务提供者都需要创建User实体。

package com.wya.springboot.controller;

public class User implements Serializable{
    private static final long serialVersionUID = -3653242135661883164L;
	private String name;
    private Integer age;

    public User() {
    }

    public User(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "name=" + name + ", age=" +age;
    }

}

Spring Cloud系列（七）RestTemplate详解

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