RestTemplate使用详解

                 RestTemplate使用详解

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

我之前的HTTP开发是用apache的HttpClient开发，代码复杂，还得操心资源回收等。代码很复杂，冗余代码多，稍微截个图，这是我封装好的一个post请求工具：

 

本教程将带领大家实现Spring生态内RestTemplate的Get请求和Post请求还有exchange指定请求类型的实践和RestTemplate核心方法源码的分析，看完你就会用优雅的方式来发HTTP请求。

1. 简述RestTemplate

是Spring用于同步client端的核心类，简化了与http服务的通信，并满足RestFul原则，程序代码可以给它提供URL，并提取结果。默认情况下，RestTemplate默认依赖jdk的HTTP连接工具。当然你也可以 通过setRequestFactory属性切换到不同的HTTP源，比如Apache HttpComponents、Netty和OkHttp。

RestTemplate能大幅简化了提交表单数据的难度，并且附带了自动转换JSON数据的功能，但只有理解了HttpEntity的组成结构（header与body），且理解了与uriVariables之间的差异，才能真正掌握其用法。这一点在Post请求更加突出，下面会介绍到。

该类的入口主要是根据HTTP的六个方法制定：

HTTP method	RestTemplate methods
DELETE	delete
GET	getForObject
	getForEntity
HEAD	headForHeaders
OPTIONS	optionsForAllow
POST	postForLocation
	postForObject
PUT	put
any	exchange
	execute

此外，exchange和excute可以通用上述方法。

在内部，RestTemplate默认使用HttpMessageConverter实例将HTTP消息转换成POJO或者从POJO转换成HTTP消息。默认情况下会注册主mime类型的转换器，但也可以通过setMessageConverters注册其他的转换器。(其实这点在使用的时候是察觉不到的，很多方法有一个responseType 参数，它让你传入一个响应体所映射成的对象，然后底层用HttpMessageConverter将其做映射)

HttpMessageConverterExtractor responseExtractor =
                new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);

HttpMessageConverter.java源码：

public interface HttpMessageConverter {
        //指示此转换器是否可以读取给定的类。
    boolean canRead(Class clazz, @Nullable MediaType mediaType);

        //指示此转换器是否可以写给定的类。
    boolean canWrite(Class clazz, @Nullable MediaType mediaType);

        //返回List
    List getSupportedMediaTypes();

        //读取一个inputMessage
    T read(Class clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException;

        //往output message写一个Object
    void write(T t, @Nullable MediaType contentType, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException;

}

在内部，RestTemplate默认使用SimpleClientHttpRequestFactory和DefaultResponseErrorHandler来分别处理HTTP的创建和错误，但也可以通过setRequestFactory和setErrorHandler来覆盖。

2. get请求实践

2.1. getForObject()方法

public  T getForObject(String url, Class responseType, Object... uriVariables){}
public  T getForObject(String url, Class responseType, Map uriVariables)
public  T getForObject(URI url, Class responseType)

getForObject()其实比getForEntity()多包含了将HTTP转成POJO的功能，但是getForObject没有处理response的能力。因为它拿到手的就是成型的pojo。省略了很多response的信息。

2.1.1 POJO:

public class Notice {
    private int status;
    private Object msg;
    private List data;
}
public  class DataBean {
  private int noticeId;
  private String noticeTitle;
  private Object noticeImg;
  private long noticeCreateTime;
  private long noticeUpdateTime;
  private String noticeContent;
}

示例：2.1.2 不带参的get请求

    /**
     * 不带参的get请求
     */
    @Test
    public void restTemplateGetTest(){
        RestTemplate restTemplate = new RestTemplate();
        Notice notice = restTemplate.getForObject("http://xxx.top/notice/list/1/5"
                , Notice.class);
        System.out.println(notice);
    }

控制台打印：

INFO 19076 --- [           main] c.w.s.c.w.c.HelloControllerTest          
: Started HelloControllerTest in 5.532 seconds (JVM running for 7.233)

Notice{status=200, msg=null, data=[DataBean{noticeId=21, noticeTitle='aaa', noticeImg=null, 
noticeCreateTime=1525292723000, noticeUpdateTime=1525292723000, noticeContent='
aaa
'}, 
DataBean{noticeId=20, noticeTitle='ahaha', noticeImg=null, noticeCreateTime=1525291492000, 
noticeUpdateTime=1525291492000, noticeContent='
ah.......'

示例：2.1.3 带参数的get请求1

Notice notice = restTemplate.getForObject("http://fantj.top/notice/list/{1}/{2}"
                , Notice.class,1,5);

明眼人一眼能看出是用了占位符{1}。

示例：2.1.4 带参数的get请求2

        Map map = new HashMap();
        map.put("start","1");
        map.put("page","5");
        Notice notice = restTemplate.getForObject("http://fantj.top/notice/list/"
                , Notice.class,map);

明眼人一看就是利用map装载参数，不过它默认解析的是PathVariable的url形式。

2.2 getForEntity()方法

public  ResponseEntity getForEntity(String url, Class responseType, Object... uriVariables){}
public  ResponseEntity getForEntity(String url, Class responseType, Map uriVariables){}
public  ResponseEntity getForEntity(URI url, Class responseType){}

与getForObject()方法不同的是返回的是ResponseEntity对象，如果需要转换成pojo，还需要json工具类的引入，这个按个人喜好用。不会解析json的可以百度FastJson或者Jackson等工具类。然后我们就研究一下ResponseEntity下面有啥方法。

ResponseEntity、HttpStatus、BodyBuilder结构

ResponseEntity.java

public HttpStatus getStatusCode(){}
public int getStatusCodeValue(){}
public boolean equals(@Nullable Object other) {}
public String toString() {}
public static BodyBuilder status(HttpStatus status) {}
public static BodyBuilder ok() {}
public static  ResponseEntity ok(T body) {}
public static BodyBuilder created(URI location) {}
...

HttpStatus.java

public enum HttpStatus {
public boolean is1xxInformational() {}
public boolean is2xxSuccessful() {}
public boolean is3xxRedirection() {}
public boolean is4xxClientError() {}
public boolean is5xxServerError() {}
public boolean isError() {}
}

BodyBuilder.java

public interface BodyBuilder extends HeadersBuilder {
    //设置正文的长度，以字节为单位，由Content-Length标头
      BodyBuilder contentLength(long contentLength);
    //设置body的MediaType 类型
      BodyBuilder contentType(MediaType contentType);
    //设置响应实体的主体并返回它。
       ResponseEntity body(@Nullable T body);
｝

可以看出来，ResponseEntity包含了HttpStatus和BodyBuilder的这些信息，这更方便我们处理response原生的东西。

示例：

@Test
public void rtGetEntity(){
        RestTemplate restTemplate = new RestTemplate();
        ResponseEntity entity = restTemplate.getForEntity("http://fantj.top/notice/list/1/5"
                , Notice.class);

        HttpStatus statusCode = entity.getStatusCode();
        System.out.println("statusCode.is2xxSuccessful()"+statusCode.is2xxSuccessful());

        Notice body = entity.getBody();
        System.out.println("entity.getBody()"+body);


        ResponseEntity.BodyBuilder status = ResponseEntity.status(statusCode);
        status.contentLength(100);
        status.body("我在这里添加一句话");
        ResponseEntity> body1 = status.body(Notice.class);
        Class body2 = body1.getBody();
        System.out.println("body1.toString()"+body1.toString());
    }

statusCode.is2xxSuccessful()true
entity.getBody()Notice{status=200, msg=null, data=[DataBean{noticeId=21, noticeTitle='aaa', ...
body1.toString()<200 OK,class com.waylau.spring.cloud.weather.pojo.Notice,{Content-Length=[100]}>

当然，还有getHeaders()等方法没有举例。

3. post请求实践

同样的,post请求也有postForObject和postForEntity。

public  T postForObject(String url, @Nullable Object request, Class responseType, Object... uriVariables)
            throws RestClientException {}
public  T postForObject(String url, @Nullable Object request, Class responseType, Map uriVariables)
            throws RestClientException {}
public  T postForObject(URI url, @Nullable Object request, Class responseType) throws RestClientException {}

示例

我用一个验证邮箱的接口来测试。

@Test
public void rtPostObject(){
    RestTemplate restTemplate = new RestTemplate();
    String url = "http://47.xxx.xxx.96/register/checkEmail";
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
    MultiValueMap map= new LinkedMultiValueMap<>();
    map.add("email", "[email protected]");

    HttpEntity> request = new HttpEntity<>(map, headers);
    ResponseEntity response = restTemplate.postForEntity( url, request , String.class );
    System.out.println(response.getBody());
}

执行结果：

{"status":500,"msg":"该邮箱已被注册","data":null}

代码中，MultiValueMap是Map的一个子类，它的一个key可以存储多个value，简单的看下这个接口：

public interface MultiValueMap extends Map> {...}

为什么用MultiValueMap?因为HttpEntity接受的request类型是它。

public HttpEntity(@Nullable T body, @Nullable MultiValueMap headers){}
我这里只展示它的一个construct,从它可以看到我们传入的map是请求体，headers是请求头。

为什么用HttpEntity是因为restTemplate.postForEntity方法虽然表面上接收的request是@Nullable Object request类型，但是你追踪下去会发现，这个request是用HttpEntity来解析。核心代码如下：

if (requestBody instanceof HttpEntity) {
    this.requestEntity = (HttpEntity) requestBody;
}else if (requestBody != null) {
    this.requestEntity = new HttpEntity<>(requestBody);
}else {
    this.requestEntity = HttpEntity.EMPTY;
}

我曾尝试用map来传递参数，编译不会报错，但是执行不了，是无效的url request请求(400 ERROR)。其实这样的请求方式已经满足post请求了，cookie也是属于header的一部分。可以按需求设置请求头和请求体。其它方法与之类似。

4. 使用exchange指定调用方式

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。

但是你会发现exchange的方法中似乎都有@Nullable HttpEntity requestEntity这个参数，这就意味着我们至少要用HttpEntity来传递这个请求体，之前说过源码所以建议就使用HttpEntity提高性能。

示例

    @Test
    public void rtExchangeTest() throws JSONException {
        RestTemplate restTemplate = new RestTemplate();
        String url = "http://xxx.top/notice/list";
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
        JSONObject jsonObj = new JSONObject();
        jsonObj.put("start",1);
        jsonObj.put("page",5);

        HttpEntity entity = new HttpEntity<>(jsonObj.toString(), headers);
        ResponseEntity exchange = restTemplate.exchange(url, 
                                          HttpMethod.GET, entity, JSONObject.class);
        System.out.println(exchange.getBody());
    }

这次可以看到，我使用了JSONObject对象传入和返回。

当然，HttpMethod方法还有很多，用法类似。

5. excute()指定调用方式

excute()的用法与exchange()大同小异了，它同样可以指定不同的HttpMethod，不同的是它返回的对象是响应体所映射成的对象，而不是ResponseEntity。

需要强调的是，execute()方法是以上所有方法的底层调用。随便看一个：

    @Override
    @Nullable
    public  T postForObject(String url, @Nullable Object request, Class responseType, Map uriVariables)
            throws RestClientException {

        RequestCallback requestCallback = httpEntityCallback(request, responseType);
        HttpMessageConverterExtractor responseExtractor =
                new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
        return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
    }

在项目中，当我们需要远程调用一个HTTP接口时，我们经常会用到RestTemplate这个类。这个类是Spring框架提供的一个工具类。Spring官网对它的介绍如下：

RestTemplate: The original Spring REST client with a synchronous, template method API.

从上面的介绍中我们可以知道：RestTemplate是一个同步的Rest API客户端。下面我们就来介绍下RestTemplate的常用功能。

RestTemplate简单使用#

RestTemplate提供高度封装的接口，可以让我们非常方便地进行Rest API调用。常见的方法如下：

表格：RestTemplate的方法

上面的方法我们大致可以分为三组：

• getForObject --- optionsForAllow分为一组，这类方法是常规的Rest API（GET、POST、DELETE等）方法调用；
• exchange：接收一个RequestEntity 参数，可以自己设置HTTP method, URL, headers和body。返回ResponseEntity。
• execute：通过callback 接口，可以对请求和返回做更加全面的自定义控制。

一般情况下，我们使用第一组和第二组方法就够了。

创建RestTemplate#

@Bean
public RestTemplate restTemplate(ClientHttpRequestFactory factory) {
    RestTemplate restTemplate = new RestTemplate(factory);
    return restTemplate;
}

@Bean
public ClientHttpRequestFactory simpleClientHttpRequestFactory() {
    SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();
    factory.setReadTimeout(5000);
    factory.setConnectTimeout(15000);
    //设置代理
    //factory.setProxy(null);
    return factory;
}

创建RestTemplate时需要一个ClientHttpRequestFactory，通过这个请求工厂，我们可以统一设置请求的超时时间，设置代理以及一些其他细节。通过上面代码配置后，我们直接在代码中注入RestTemplate就可以使用了。

接口调用#

1. 普通接口调用

Map vars = Collections.singletonMap("hotel", "42");
//通过GET方式调用，返回一个String值，还可以给URL变量设置值（也可通过uriTemplateHandler这个属性自定义）
String result = restTemplate.getForObject(
        "https://example.com/hotels/{hotel}/rooms/{hotel}", String.class, vars);

String url = "http://127.0.0.1:8080/hello";
JSONObject param = new JSONObject();
//restTemplate会根据params的具体类型，调用合适的HttpMessageConvert将请求参数写到请求体body中，并在请求头中添加合适的content-type；
//也会根据responseType的类型（本列子中是JSONObject），设置head中的accept字段，当响应返回的时候再调用合适的HttpMessageConvert进行响应转换
ResponseEntity responseEntity=restTemplate.postForEntity(url,params,JSONObject.class);
int statusCodeValue = responseEntity.getStatusCodeValue();
HttpHeaders headers = responseEntity.getHeaders();
JSONObject body = responseEntity.getBody();

2. 添加Header和Cookie

有时候，我们需要在请求中的Head中添加值或者将某些值通过cookie传给服务端，那么上面这种调用形式就不太满足要求了。

 UriComponents uriComponents = UriComponentsBuilder.fromHttpUrl("127.0.0.1:8080").
                path("/test").build(true);
 URI uri = uriComponents.toUri();
 
RequestEntity requestEntity = RequestEntity.post(uri).
                //添加cookie(这边有个问题，假如我们要设置cookie的生命周期，作用域等参数我们要怎么操作)
                header(HttpHeaders.COOKIE,"key1=value1").
                //添加header
                header(("MyRequestHeader", "MyValue")
                accept(MediaType.APPLICATION_JSON).
                contentType(MediaType.APPLICATION_JSON).
                body(requestParam);
ResponseEntity responseEntity = restTemplate.exchange(requestEntity,JSONObject.class);
//响应结果
JSONObject responseEntityBody = responseEntity.getBody();

3. 文件上传

上面两个列子基本能覆盖我们平时开发的大多数功能了。这边再讲个文件上传的列子（RestTemplate功能还是蛮全的）。

public Object uplaod(@RequestBody JSONObject params) throws Exception{

        final String url = "http://localhost:8888/hello/m3";
        //设置请求头
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.MULTIPART_FORM_DATA);
        //设置请求体，注意是LinkedMultiValueMap
        FileSystemResource resource1 = new FileSystemResource("D:\\dir1\\ss\\pic1.jpg");
        FileSystemResource resource2 = new FileSystemResource("D:\\dir1\\ss\\pic2.jpg");
       
        MultiValueMap form = new LinkedMultiValueMap<>();
        form.add("file", resource1);
        form.add("file", resource2);
        form.add("param1","value1");

        HttpEntity> files = new HttpEntity<>(form, headers);
        JSONObject s = restTemplate.postForObject(url, files, JSONObject.class);
        return s;
    }

上面的代码中上传了两个本地图片，通过下面代码可以顺利接收。

@RequestMapping("/m3")
public Object fileUpload(@RequestParam("file") MultipartFile[] files, HttpServletRequest request) throws Exception {
    //携带的其他参数可以使用getParameter方法接收
    String param1 = request.getParameter("param1");
    Response response = new Response();
    if (files == null) {
        response.failure("文件上传错误,服务端未拿到上传的文件！");
        return response;
    }
    for (MultipartFile file : files) {
        if (!file.isEmpty() && file.getSize() > 0) {
            String fileName = file.getOriginalFilename();
            //参考FileCopyUtils这个工具类
            file.transferTo(new File("D:\\" + fileName));
            logger.info("文件:{} 上传成功...",fileName);
        }
    }
    response.success("文件上传成功");
    return response;
    }

但是我们发现上面的上传代码中，上传文件的类必须使用FileSystemResource。有时我们会碰到这种情况：文件我们会从文件服务下载到内存中一个InputStream的形式存在，那此时在使用FileSystemResource就不行了。

当然，我们使用讨巧一点的办法也是可以的：先将下载下来的InputStream保存到本地，然后再读取到FileSystemResource，上传后再删除本地临时文件。

但是总觉得这个方法不够完美。最后发现有个同事已经写了相关的实现。这边就直接拿来用了。

//自己实现了一个Resource
public class InMemoryResource extends ByteArrayResource {
    private final String filename;
    private final long lastModified;

    public InMemoryResource(String filename, String description, byte[] content, long lastModified) {
        super(content, description);
        this.lastModified = lastModified;
        this.filename = filename;
    }
    
    @Override
    public long lastModified() throws IOException {
        return this.lastModified;
    }

    @Override
    public String getFilename() {
        return this.filename;
    }
}

调整后的上传代码

 @PostMapping("/m3")
    public Object m3(@RequestBody JSONObject params) throws Exception{

        final String url = "http://localhost:8888/hello/m3";
        //设置请求头
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.MULTIPART_FORM_DATA);
        //设置请求体，注意是LinkedMultiValueMap
        //下面两个流从文件服务下载，这边省略（注意最后关闭流）
        InputStream fis1 = 
        InputStream fis2 = 

        InMemoryResource resource1 = new InMemoryResource("file1.jpg","description1", FileCopyUtils.copyToByteArray(fis1), System.currentTimeMillis());
        InMemoryResource resource2 = new InMemoryResource("file2.jpg","description2", FileCopyUtils.copyToByteArray(fis2), System.currentTimeMillis());
        MultiValueMap form = new LinkedMultiValueMap<>();
        form.add("file", resource1);
        form.add("file", resource2);
        form.add("param1","value1");

        HttpEntity> files = new HttpEntity<>(form, headers);
        JSONObject s = restTemplate.postForObject(url, files, JSONObject.class);
        return s;
    }

一些其他设置#

1. 拦截器配置

RestTemplate也可以设置拦截器做一些统一处理。这个功能感觉和Spring MVC的拦截器类似。配置也很简单：

class MyInterceptor implements ClientHttpRequestInterceptor{

        @Override
        public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
            logger.info("enter interceptor...");
            return execution.execute(request,body);
        }
    }

 @Bean
public RestTemplate restTemplate(ClientHttpRequestFactory factory) {
    RestTemplate restTemplate = new RestTemplate(factory);
    MyInterceptor myInterceptor = new MyInterceptor();
    List list = new ArrayList<>();
    list.add(myInterceptor);
    restTemplate.setInterceptors(list);
    return restTemplate;
}

2. ErrorHandler配置

ErrorHandler用来对调用错误对统一处理。

public class MyResponseErrorHandler extends DefaultResponseErrorHandler {

        @Override
        public boolean hasError(ClientHttpResponse response) throws IOException {
            return super.hasError(response);
        }

        @Override
        public void handleError(ClientHttpResponse response) throws IOException {
            HttpStatus statusCode = HttpStatus.resolve(response.getRawStatusCode());
            if (statusCode == null) {
                throw new UnknownHttpStatusCodeException(response.getRawStatusCode(), response.getStatusText(),
                        response.getHeaders(), getResponseBody(response), getCharset(response));
            }
            handleError(response, statusCode);
        }
        @Override
        protected void handleError(ClientHttpResponse response, HttpStatus statusCode) throws IOException {
            switch (statusCode.series()) {
                case CLIENT_ERROR:
                    HttpClientErrorException exp1 = new HttpClientErrorException(statusCode, response.getStatusText(), response.getHeaders(), getResponseBody(response), getCharset(response));
                    logger.error("客户端调用异常",exp1);
                    throw  exp1;
                case SERVER_ERROR:
                    HttpServerErrorException exp2 = new HttpServerErrorException(statusCode, response.getStatusText(),
                            response.getHeaders(), getResponseBody(response), getCharset(response));
                    logger.error("服务端调用异常",exp2);
                    throw exp2;
                default:
                    UnknownHttpStatusCodeException exp3 = new UnknownHttpStatusCodeException(statusCode.value(), response.getStatusText(),
                            response.getHeaders(), getResponseBody(response), getCharset(response));
                    logger.error("网络调用未知异常");
                    throw exp3;
            }
        }

    }

@Bean
public RestTemplate restTemplate(ClientHttpRequestFactory factory) {
    RestTemplate restTemplate = new RestTemplate(factory);
    MyResponseErrorHandler errorHandler = new MyResponseErrorHandler();
    restTemplate.setErrorHandler(errorHandler);
    List> messageConverters = restTemplate.getMessageConverters();
    //通过下面代码可以添加新的HttpMessageConverter
    //messageConverters.add(new );
    return restTemplate;
}

3. HttpMessageConverter配置
RestTemplate 也可以配置HttpMessageConverter，配置的原理和Spring MVC中类似。

简单总结#

通过RestTemplate，我们可以非常方便的进行Rest API调用。但是在Spring 5中已经不再建议使用RestTemplate，而是建议使用WebClient。WebClient是一个支持异步调用的Client。所以喜欢研究新东西的同学可以开始研究下新东西了。

 

同步RestTemplate和异步AsyncRestTemplate

我编写了以下代码来测试同步RestTemplate和AsyncRestTemplate的性能.我只是在POSTMAN上手动运行了几次.

我们只是将10个引用传递给GET调用,以便我们可以返回10个链接：

RestTemplate – 同步并在2806ms返回：

ArrayList references = new ArrayList<>();
ArrayList links = new ArrayList<>();
RestTemplate restTemplate = new RestTemplate(); 
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());
for (int i = 0; i < 10; i++) {
    ResponseEntity resource = restTemplate.getForEntity(references.get(i), String.class);
    links.add(resource.getBody().toString());
}
复制代码

RestTemplate – 异步并返回2794ms：

//Creating a synchronizedList so that when the async resttemplate returns, there will be no concurrency issues
List links = Collections.synchronizedList(new ArrayList());

//CustomClientHttpRequestFactory just extends SimpleClientHttpRequestFactory but disables automatic redirects in SimpleClientHttpRequestFactory
CustomClientHttpRequestFactory customClientHttpRequestFactory = new CustomClientHttpRequestFactory();
//Setting the ThreadPoolTaskExecutor for the Async calls
org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor pool = new org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor();
pool.setCorePoolSize(5);
pool.setMaxPoolSize(10);
pool.setWaitForTasksToCompleteOnShutdown(true);
pool.initialize();
//Setting the TaskExecutor to the ThreadPoolTaskExecutor
customClientHttpRequestFactory.setTaskExecutor(pool);

ArrayList references = new ArrayList<>();
ArrayList links = new ArrayList<>();
AsyncRestTemplate asyncRestTemplate = new AsyncRestTemplate(customClientHttpRequestFactory); 
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());
for (int i = 0; i < 10; i++) {
    Future> resource = asyncRestTemplate.getForEntity(references.get(i), String.class);
    ResponseEntity entity = resource.get(); //this should start up 10 threads to get the links asynchronously
    links.add(entity.getBody().toString());
}
复制代码

在大多数情况下,两种方法实际上都以非常相似的时间返回结果,在异步和同步调用中平均为2800ms.

我做错了什么,因为我希望异步调用更快？

最佳答案

我会说你在这里错过了AsyncRest的真正好处.
您应该为要发送的每个请求添加回调,以便响应仅在可用时进行处理.

实际上,AsyncRestTemplate的getForEntity方法返回一个可以连接回调任务的ListenableFuture.有关详细信息,请参阅官方文档ListenableFuture.

例如,在您的情况下,它可能是：

for (int i = 0; i < 10; i++) {
     ListenableFuture> response = asyncRestTemplate.getForEntity(references.get(i), String.class);
     response.addCallback(new ListenableFutureCallback>() {
            @Override
            public void onSuccess(ResponseEntity result) {
                // Do stuff onSuccess 
                links.add(result.getBody().toString());
            }

            @Override
            public void onFailure(Throwable ex) {
                log.warn("Error detected while submitting a REST request. Exception was {}", ex.getMessage());
            }
        });
}

 

RestTemplate整合HttpClient、Okhttp

 

HttpClient入门

• 确定maven环境

   
    
        org.springframework.boot
        spring-boot-starter-parent
        2.1.4.RELEASE
    

    
        
        
            org.springframework.boot
            spring-boot-starter-web
        
        
        
            org.apache.httpcomponents
            httpclient
            4.5.6
        
        
        
            lombok
            lombok
            1.0
        
        
        
            com.alibaba
            fastjson
            1.2.49
        
        
            org.springframework.boot
            spring-boot-starter-test
        
    

• 使用HttpClient发送Get请求

		CloseableHttpClient httpClient = null;
        CloseableHttpResponse response = null;
		try {
            //1 创建Httpclient对象(默认连接),相当于打开了浏览器
            CloseableHttpClient httpClient = HttpClients.createDefault();

            //2 确定请求方式和请求路径，相当于在浏览器输入地址
            HttpGet httpGet = new HttpGet("http://localhost:9090/user");

            //3 执行请求并获取响应，相当于敲完地址后按下回车。
            CloseableHttpResponse response = httpClient.execute(httpGet);

            //4 判断状态码
            if(response.getStatusLine().getStatusCode() == 200){
                //5.1 获得响应数据的类型
                System.out.println(response.getEntity().getContentType());
                //5.2 获得响应体内容并使用EntityUtils工具进行处理
                String str = EntityUtils.toString(response.getEntity(),"UTF-8");
                System.out.println(str);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }finally {
          //6 释放资源
          response.close();
          httpClient.close();
        }

• 使用HttpClient发送Post请求

  		CloseableHttpClient httpClient = null;
          CloseableHttpResponse response = null;
          try {
              httpClient = HttpClients.createDefault();
  
              HttpPost httpPost = new HttpPost("http://localhost:9090/user");
              //  设置请求头
              httpPost.setHeader("content-type","application/json;charset=utf-8");
              //  设置并处理请求体
              String str = "{\"username\":\"jack\",\"password\":\"1111\"}";
              httpPost.setEntity(new StringEntity(str,"utf-8"));
  
              response = httpClient.execute(httpPost);
  
              if (response.getStatusLine().getStatusCode() == 200){
                  System.out.println(EntityUtils.toString(response.getEntity()));
              }
          } catch (IOException e) {
              e.printStackTrace();
          }finally {
              response.close();
              httpClient.close();
          }
  

• 使用HttpClient发送Put请求

  		CloseableHttpClient httpClient = null;
          CloseableHttpResponse response = null;
          try {
              httpClient = HttpClients.createDefault();
              HttpPut httpPut = new HttpPut("http://localhost:9090/user");
              httpPut.setHeader("content-type","application/json;charset=utf-8");
              String jsonStr = JSON.toJSONString(new User(1, "jack", "1111", 18));
              httpPut.setEntity(new StringEntity(jsonStr,"utf-8"));
  
              response = httpClient.execute(httpPut);
  
              if (response.getStatusLine().getStatusCode() == 200){
                  System.out.println(EntityUtils.toString(response.getEntity()));
              }
          } catch (IOException e) {
              e.printStackTrace();
          } finally {
              response.close();
              httpClient.close();
          }
  

• 使用HttpClient发送Delete请求

  		CloseableHttpClient httpClient = null;
          CloseableHttpResponse response = null;
          try {
              //1, 创建客户端
              httpClient = HttpClients.createDefault();
              //2, 创建DELETE实例
              HttpDelete httpDelete = new HttpDelete("http://localhost:9090/user/1");
              //3, 发送请求
              response = httpClient.execute(httpDelete);
              //4, 判断状态码
              if (response.getStatusLine().getStatusCode() == 200){
                  //5, 实用工具处理响应数据
                  System.out.println(EntityUtils.toString(response.getEntity()));
              }
          } catch (IOException e) {
              e.printStackTrace();
          } finally {
              //6, 释放资源
              response.close();
              httpClient.close();
          }
  

4.RestTemplate

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

  ​ RestTemplate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

• Get请求

    [@Test](https://my.oschina.net/azibug)
      public void testGet(){
          RestTemplate restTemplate = new RestTemplate();
          //  设置url,返回值类型
          ResponseEntity entity = restTemplate.getForEntity("http://localhost:9090/user", BaseResult.class);
          //  返回状态码
          System.out.println(entity.getStatusCode());
          //  返回响应体
          System.out.println(entity.getBody().getData());
      }
  

• Post请求

   [@Test](https://my.oschina.net/azibug)
      public void testLogin(){
          RestTemplate restTemplate = new RestTemplate();
          //  设置url,请求体(自动处理),返回值类型
          ResponseEntity entity = restTemplate.postForEntity("http://localhost:9090/user/login", new User(1,"jack","1234",18), User.class);
          System.out.println(entity.getStatusCodeValue());
          System.out.println(entity.getBody());
      }
  

• Put请求

  [@Test](https://my.oschina.net/azibug)
      public void testPut(){
          RestTemplate restTemplate = new RestTemplate();
           //  设置url
          restTemplate.put("http://localhost:9090/user",new User(1,"jack","1234",18));
          System.out.println("修改成功");
      }
  

• Delete请求

   [@Test](https://my.oschina.net/azibug)
      public void testDelete(){
          RestTemplate restTemplate = new RestTemplate();
          //  设置url
          restTemplate.delete("http://localhost:9090/user/1");
          System.out.println(" 删除成功");
      }
  

5.SpringBoot 整合 HttpClient及RestTemplate自定义连接池

package com.czxy.config;

import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
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.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.web.client.RestTemplate;

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

/**
 * Created by 澈 on 2019/12/3.
 */
@Configuration
public class HttpClientConfig {

    //1. 自定义连接 httpClient
    @Bean
    public CloseableHttpClient httpClient(PoolingHttpClientConnectionManager connectionManager,
                                          RequestConfig requestConfig){
        return HttpClients.custom()
                .setConnectionManager(connectionManager)
                .setDefaultRequestConfig(requestConfig)
                .build();
    }

    //2. 配置PoolingHttpClientConnectionManager
    @Bean
    public PoolingHttpClientConnectionManager connectionManager(){
        //1.  HttpClient连接管理器
        PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
        //1.1.  最大连接数
        connectionManager.setMaxTotal(1000);
        //1.2.  设置并发访问数
        connectionManager.setDefaultMaxPerRoute(20);

        return connectionManager;
    }

    //3. 配置RequestConfig
    @Bean
    public RequestConfig requestConfig(){
        //1.3.  请求配置RequestConfig
        return RequestConfig.custom()
                .setConnectTimeout(1000)
                .setConnectionRequestTimeout(500)
                .setSocketTimeout(10 * 1000)
                .build();
    }

    //4. 创建一个工厂
    @Bean
    public ClientHttpRequestFactory requestFactory(HttpClient httpClient){
        return new HttpComponentsClientHttpRequestFactory(httpClient);
    }

    //5. 配置restTemplate
    @Bean
    public RestTemplate restTemplate(ClientHttpRequestFactory requestFactory){
        RestTemplate template = new RestTemplate(requestFactory);
        //乱码处理
        List> list = template.getMessageConverters();
        for (HttpMessageConverter mc : list) {
            if (mc instanceof StringHttpMessageConverter) {
                ((StringHttpMessageConverter) mc).setDefaultCharset(Charset.forName("UTF-8"));
            }
        }
        return template;
    }
}

6.整合SpringBoot测试类

• 在测试代码中可以进行Spring容器的注册

package com.czxy;

import com.alibaba.fastjson.JSON;
import com.czxy.domain.User;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.util.EntityUtils;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.web.client.RestTemplate;

import javax.annotation.Resource;
import java.io.IOException;

/**
 * Created by 澈 on 2019/12/4.
 */
@RunWith(SpringRunner.class)    //spring 整合junit
@SpringBootTest(classes = HttpClientApplication.class)      //spring整合启动类
public class Test04 {
  	
    @Resource
    private CloseableHttpClient httpClient;
    @Resource
    private RestTemplate restTemplate;
    @Resource
    private PoolingHttpClientConnectionManager connectionManager;
    @Resource
    private RequestConfig requestConfig;

    @Test
    public void testDemo02(){
        System.out.println(httpClient);
        System.out.println(restTemplate);
        System.out.println(connectionManager);
        System.out.println(requestConfig);
    }
}

springboot装配OkHttp组件

在SpringBoot应用中，发送Http通常我们使用RestTemplate，但有部分组件底层是使用OkHttp进行Http的操作，而且OKHttp也是一个很优秀的HTTP组件。

RestTempate的springboot封装参考：https://www.cnblogs.com/yangzhilong/p/6640207.html

application.yml

okhttp:
  connect-timeout-ms: 500
  keep-alive-duration-sec: 5000
  max-idle: 100
  read-timeout-ms: 500
  write-timeout-ms: 500

Configuration：

import java.util.concurrent.TimeUnit;

import javax.annotation.Resource;
import javax.validation.constraints.NotNull;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
import org.springframework.validation.annotation.Validated;

import com.longge.gateway.util.OkHttpUtils;

import lombok.Getter;
import lombok.Setter;
import okhttp3.ConnectionPool;
import okhttp3.OkHttpClient;

/**
 * @author roger yang
 * @date 9/16/2019
 */
public class OkHttpConfiguration {
    @Resource
    private OkHttpConfig okHttpConfig;
    
    @Bean
    public OkHttpClient okHttpClient() {
        OkHttpClient client = new OkHttpClient.Builder()
                .retryOnConnectionFailure(false)
                .connectionPool(pool())
                .connectTimeout(okHttpConfig.getConnectTimeoutMs(), TimeUnit.MILLISECONDS)
                .readTimeout(okHttpConfig.getReadTimeoutMs(), TimeUnit.MILLISECONDS)
                .writeTimeout(okHttpConfig.getWriteTimeoutMs(),TimeUnit.MILLISECONDS)
                .build();
        
        OkHttpUtils.setOkHttpClient(client);
        return client;
    }
    
    @Bean
    public ConnectionPool pool() {
        return new ConnectionPool(okHttpConfig.getMaxIdle(), okHttpConfig.getKeepAliveDurationSec(), TimeUnit.SECONDS);
    }
    
    @Component
    @ConfigurationProperties(prefix = "okhttp")
    @Getter
    @Setter
    @Validated
    static class OkHttpConfig {
        @NotNull
        private Long connectTimeoutMs;
        @NotNull
        private Long readTimeoutMs;
        @NotNull
        private Long writeTimeoutMs;
        @NotNull
        private Integer maxIdle;
        @NotNull
        private Long keepAliveDurationSec;
    }
}

 

Util帮助类：

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Map;
import java.util.Objects;

import com.alibaba.fastjson.JSONObject;

import lombok.NonNull;
import okhttp3.Callback;
import okhttp3.FormBody;
import okhttp3.Headers;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

/**
 * 参数中Callback表示发送异步请求
 * @author roger yang
 * @date 9/16/2019
 */
public class OkHttpUtils {
    private static OkHttpClient okHttpClient;

    public static void setOkHttpClient(OkHttpClient client) {
        okHttpClient = client;
    }
    
    /**
     * GET Method begin---------------------------------
     */
    
    public static  T get(@NonNull String url, Class clasz) {
        return get(url, null, null, clasz);
    }
    
    public static void get(@NonNull String url, Callback callback) {
        get(url, null, null, callback);
    }

    public static  T get(@NonNull String url, Map queryParameter, Class clasz) {
        return get(url, null, queryParameter, clasz);
    }
    
    public static void get(@NonNull String url, Map queryParameter, Callback callback) {
        get(url, null, queryParameter, callback);
    }

    public static  T get(@NonNull String url, Map headerParameter, Map queryParameter, Class clasz) {
        Request request = processGetParameter(url, headerParameter, queryParameter);

        try (Response resp = okHttpClient.newCall(request).execute();) {
            return processResponse(resp, clasz);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
    
    public static void get(@NonNull String url, Map headerParameter, Map queryParameter, Callback callback) {
        Request request = processGetParameter(url, headerParameter, queryParameter);
        okHttpClient.newCall(request).enqueue(callback);
    }
    
    private static Request processGetParameter(String url, Map headerParameter, Map queryParameter) {
        Request.Builder builder = new Request.Builder();
        if (!isEmptyMap(headerParameter)) {
            builder.headers(Headers.of(headerParameter));
        }
        if (isEmptyMap(queryParameter)) {
            builder.url(url);
        } else {
            boolean hasQuery = false;
            try {
                hasQuery = new URL(url).getQuery().isEmpty();
            } catch (MalformedURLException e) {
                throw new RuntimeException("url is illegal");
            }
            StringBuilder sb = new StringBuilder(url);
            if (!hasQuery) {
                sb.append("?1=1");
            }
            queryParameter.forEach((k, v) -> {
                sb.append("&").append(k).append("=").append(v);
            });
            builder.url(sb.toString());
        }
        return builder.build();
    }

    /**
     * POST Method With JSON begin---------------------------------
     */
    
    public static  T postJson(@NonNull String url, Class clasz) {
        return postJson(url, null, null, clasz);
    }
    
    public static void postJson(@NonNull String url, Callback callback) {
        postJson(url, null, null, callback);
    }

    public static  T postJson(@NonNull String url, Map headerParameter, Class clasz) {
        return postJson(url, headerParameter, null, clasz);
    }
    
    public static void postJson(@NonNull String url, Map headerParameter, Callback callback) {
        postJson(url, headerParameter, null, callback);
    }
    
    public static  T postJson(@NonNull String url, Map headerParameter, Object bodyObj, Class clasz) {
        Request request = processPostJsonParameter(url, headerParameter, bodyObj);
        try (Response resp = okHttpClient.newCall(request).execute();) {
            return processResponse(resp, clasz);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
    public static void postJson(@NonNull String url, Map headerParameter, Object bodyObj, Callback callback) {
        Request request = processPostJsonParameter(url, headerParameter, bodyObj);
        okHttpClient.newCall(request).enqueue(callback);
    }
    
    private static Request processPostJsonParameter(String url, Map headerParameter, Object bodyObj) {
        Request.Builder builder = new Request.Builder().url(url);
        if(!Objects.isNull(bodyObj)) {
            RequestBody body = RequestBody.create(MediaType.parse("application/json; charset=utf-8"), JSONObject.toJSONString(bodyObj));
            builder.post(body);
        } else {
            RequestBody body = RequestBody.create(MediaType.parse("application/json; charset=utf-8"), "{}");
            builder.post(body);
        }
        if (!isEmptyMap(headerParameter)) {
            builder.headers(Headers.of(headerParameter));
        }
        return builder.build();
    }
    
    /**
     * POST Method With Form begin---------------------------------
     */
    
    public static  T postForm(@NonNull String url, Class clasz) {
        return postForm(url, null, null, clasz);
    }
    
    public static void postForm(@NonNull String url, Callback callback) {
        postForm(url, null, null, callback);
    }

    public static  T postForm(@NonNull String url, Map headerParameter, Class clasz) {
        return postForm(url, headerParameter, null, clasz);
    }
    
    public static void postForm(@NonNull String url, Map headerParameter, Callback callback) {
        postForm(url, headerParameter, null, callback);
    }
    
    public static  T postForm(@NonNull String url, Map headerParameter, Map parameters, Class clasz) {
        Request request = processPostFormParameter(url, headerParameter, parameters);
        try (Response resp = okHttpClient.newCall(request).execute();) {
            return processResponse(resp, clasz);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
    public static void postForm(@NonNull String url, Map headerParameter, Map parameters, Callback callback) {
        Request request = processPostFormParameter(url, headerParameter, parameters);
        okHttpClient.newCall(request).enqueue(callback);
    }
    
    private static Request processPostFormParameter(String url, Map headerParameter, Map parameters) {
        Request.Builder builder = new Request.Builder().url(url);
        if(!Objects.isNull(parameters)) {
            FormBody.Builder formBuilder = new FormBody.Builder();
            parameters.forEach((k, v) -> {
                formBuilder.add(k, v);
            });
            builder.post(formBuilder.build());
        }
        if (!isEmptyMap(headerParameter)) {
            builder.headers(Headers.of(headerParameter));
        }
        return builder.build();
    }
    
    @SuppressWarnings("unchecked")
    private static  T processResponse(Response resp, Class clasz) throws IOException {
        if (resp.isSuccessful()) {
            if (Objects.equals(Void.class, clasz)) {
                return null;
            }
            String respStr = resp.body().string();
            if(Objects.equals(String.class, clasz)) {
                return (T)respStr;
            }
            return JSONObject.parseObject(respStr, clasz);
        }
        return null;
    }
    
    private static boolean isEmptyMap(Map map) {
        return Objects.isNull(map) || map.isEmpty();
    }
}

GitHub地址：https://github.com/yangzhilong/new-gateway-test.git

如果想要OkHttp的装配是非自动的，可以采用自定义@EnableXX注解来实现。

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.annotation.Import;

import com.longge.gateway.configuration.OkHttpConfiguration;

/**
 * @author roger yang
 * @date 9/16/2019
 */
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 @Import(OkHttpConfiguration.class)
public @interface EnableOkHttp {

}

然后把OkHttpConfiguration类的@Configuration注解去掉，当你要用时在启动类加上@EnableOkHttp即可。

 

对于OKhttp的设置还可参考：

1、简介

OkHttp是一个高效的HTTP客户端，允许所有同一个主机地址的请求共享同一个socket连接；连接池减少请求延时；透明的GZIP压缩减少响应数据的大小；缓存响应内容，避免一些完全重复的请求

当网络出现问题的时候OkHttp依然坚守自己的职责，它会自动恢复一般的连接问题，如果你的服务有多个IP地址，当第一个IP请求失败时，OkHttp会交替尝试你配置的其他IP，OkHttp使用现代TLS技术(SNI, ALPN)初始化新的连接，当握手失败时会回退到TLS 1.0。

1）使用：它的请求/响应 API 使用构造器模式builders来设计，它支持阻塞式的同步请求和带回调的异步请求。

    com.squareup.okhttp3
    okhttp
    3.10.0

import okhttp3.ConnectionPool;
import okhttp3.OkHttpClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.OkHttp3ClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.concurrent.TimeUnit;

@Configuration
public class OkHttpRestTemplateConfig {


    @Bean("okHttpRestTemplate")
    public RestTemplate okHttpRestTemplate() {
        OkHttpClient httpClient = okHttpClient();
        ClientHttpRequestFactory factory = new OkHttp3ClientHttpRequestFactory(httpClient);
        RestTemplate restTemplate = new RestTemplate(factory);
        // 可以添加消息转换
        //restTemplate.setMessageConverters(...);
        // 可以增加拦截器
        //restTemplate.setInterceptors(...);
        return restTemplate;
    }

    @Bean
    public OkHttpClient okHttpClient() {
        return new OkHttpClient.Builder()
                //.sslSocketFactory(sslSocketFactory(), x509TrustManager())
                .retryOnConnectionFailure(false)
                .connectionPool(pool())
                .connectTimeout(30, TimeUnit.SECONDS)
                .readTimeout(30, TimeUnit.SECONDS)
                .writeTimeout(30,TimeUnit.SECONDS)
                .build();
    }

    @Bean
    public X509TrustManager x509TrustManager() {
        return new X509TrustManager() {
            @Override
            public void checkClientTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
            }
            @Override
            public void checkServerTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
            }
            @Override
            public X509Certificate[] getAcceptedIssuers() {
                return new X509Certificate[0];
            }
        };
    }

    @Bean
    public SSLSocketFactory sslSocketFactory() {
        try {
            //信任任何链接
            SSLContext sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, new TrustManager[]{x509TrustManager()}, new SecureRandom());
            return sslContext.getSocketFactory();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (KeyManagementException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * Create a new connection pool with tuning parameters appropriate for a single-user application.
     * The tuning parameters in this pool are subject to change in future OkHttp releases. Currently
     */
    @Bean
    public ConnectionPool pool() {
        return new ConnectionPool(200, 5, TimeUnit.MINUTES);
    }
}