RestTemplate负载均衡原理

自定义注解

@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface MyLoadBalanced {

}

@Configuration
public class MyConfig {

	@Autowired(required = false)
	@MyLoadBalanced
	private List<RestTemplate> tpls = Collections.emptyList();
	
	@Bean
	public SmartInitializingSingleton lbInitializing() {
		return new SmartInitializingSingleton() {

			public void afterSingletonsInstantiated() {
				for(RestTemplate tpl : tpls) {
					List<ClientHttpRequestInterceptor> interceptors = tpl.getInterceptors();
					interceptors.add(new MyInterceptor());
					tpl.setInterceptors(interceptors);
				}
				//System.out.println(tpls.size());
			}
			
		};
	}
}

public class MyRequest implements HttpRequest {
	
	HttpRequest sourceRequest;
	
	public MyRequest(HttpRequest sourceRequest) {
		this.sourceRequest = sourceRequest;
	}

	public HttpHeaders getHeaders() {
		return sourceRequest.getHeaders();
	}

	public HttpMethod getMethod() {
		return sourceRequest.getMethod();
	}

	public URI getURI() {
		try {
			URI newUri = new URI("http://localhost:8080/hello");
			return newUri;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return sourceRequest.getURI();
	}

}

自定义拦截器：

public class MyInterceptor implements ClientHttpRequestInterceptor {

	public ClientHttpResponse intercept(HttpRequest request, byte[] body,
			ClientHttpRequestExecution execution) throws IOException {
		System.out.println("===============  这是自定义拦截器");
		System.out.println("         旧的uri：" + request.getURI());
		
		HttpRequest newRequest = new MyRequest(request);
		System.out.println("         新的uri:" + newRequest.getURI());
		
		return execution.execute(newRequest, body);
	}

}

@RestController
@Configuration
public class MyController {

	@Bean
	@MyLoadBalanced
	public RestTemplate tplA() {
		return new RestTemplate();
	}
	
	@RequestMapping(value = "/call", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
	public String call() {
		RestTemplate tpl = tplA();
		String json = tpl.getForObject("http://hello-servie/call", String.class);
		return json;
	}
	
	@RequestMapping(value = "/hello", method = RequestMethod.GET)
	public String hello() {
		return "Hello World";
	}

}

启动类：

@SpringBootApplication
public class MyApp {

	public static void main(String[] args) {
		SpringApplication.run(MyApp.class, args);
	}

}

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>org.crazyit.cloud</groupId>
	<artifactId>rest-tpl-test</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
			<version>1.5.4.RELEASE</version>
		</dependency>
	</dependencies>