本文是在学习中的总结，欢迎转载但请注明出处： http://blog.csdn.net/pistolove/article/details/51428562

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Ⅰ、前言

          在上一篇博客中讲述ListenableFuture通过异步回调机制来实现请求的非阻塞。通常情况下，客户端获取数据并不会只发送一次http请求，可能会有多个http请求。这样，使用上一篇博客中的方法，就会产生大量的冗余代码，因为请求处理的代码除了一些参数不同外，其它地方都大致相同。我们发现不同请求之间的区别在于：请求地址的不同、响应类型的不同，可能还会有额外请求参数的不同。我们可以将请求数据和响应数据进行封装，这样，只需要一个字段来标识每一次http请求属于哪一个业务就可以实现批量发送http请求，整个过程是异步非阻塞的，一旦获取到数据就会触发回调函数，进而获取到响应数据，最后再进行业务逻辑相关处理。

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Ⅱ、RestTemplate简介

1、定义

          RestTemplate是Spring3.0中出现的新类，其可以简化HTTP服务器通信，处理HTTP连接，使应用程序代码通过提供url和响应类型(可能的模板变量)便可提取结果。

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2、方法

  //get方法
//其中url为请求地址，responseType为响应类(需要自己依据响应格式来确定)
//urlVariables为数组变量
public <T> T getForObject(String url, Class<T> responseType, Object... urlVariables) throws RestClientException 

//urlVariables为Map类型变量，其中key为请求字段名，value为请求字段值
public <T> T getForObject(String url, Class<T> responseType, Map<String, ?> urlVariables)

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

//ResponseEntity
public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... urlVariables) throws RestClientException

public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> urlVariables) throws RestClientException

public <T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType) throws RestClientException 


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

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

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

public <T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Object... uriVariables) throws RestClientException

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

public <T> ResponseEntity<T> postForEntity(URI url, Object request, Class<T> responseType) throws RestClientException

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3、说明

          Spring提供的RestTemplate可用于访问Rest服务的客户端，其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，但其并没有实现异步调用的功能。下面将引入Spring4.0提供的AsyncRestTemplate，该类可实现异步非阻塞处理http请求。

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Ⅲ、AsyncRestTemplate简介

1、定义

          AsyncRestTemplate是在Spring4.0中对RestTemplate进行扩展产生的新类，其为客户端提供了异步http请求处理的一种机制，通过返回ListenableFuture对象生成回调机制，以达到异步非阻塞发送http请求。

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2、方法

  //get
public <T> ListenableFuture<ResponseEntity<T>> getForEntity(String url, Class<T> responseType, Object... uriVariables) throws RestClientException

public <T> ListenableFuture<ResponseEntity<T>> getForEntity(String url, Class<T> responseType, Map<String, ?> urlVariables) throws RestClientException

public <T> ListenableFuture<ResponseEntity<T>> getForEntity(URI url, Class<T> responseType) throws RestClientException


//post
public <T> ListenableFuture<ResponseEntity<T>> postForEntity(String url, HttpEntity<?> request, Class<T> responseType, Object... uriVariables) throws RestClientException

public <T> ListenableFuture<ResponseEntity<T>> postForEntity(String url, HttpEntity<?> request, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException 

public <T> ListenableFuture<ResponseEntity<T>> postForEntity(URI url, HttpEntity<?> request, Class<T> responseType) throws RestClientException 

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3、说明

          相比于RestTemplate，AsyncRestTemplate通过回调机制能够很好地异步处理多个http请求，使得客户端在主方法中不必等待服务器响应，而是继续执行后续代码，这样就较大地提高了代码的执行效率，减少响应时间。

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Ⅳ、基于AsyncRestTemplate实现批量异步调用

          下面将介绍基于AsyncRestTemplate异步调用的轻量级框架，说框架有点吹牛皮的感觉，不过代码结构整体上看起来还是挺清晰的，如有不妥之处，请提供宝贵建议。其主要分为5个部分：业务标识、请求、响应，异步调用、请求处理。对应的类如下所示：

         业务标识：IEnum、UserEnum(具体业务标识)

         请求：BaseRequest、UserRequest(具体业务请求)、ConcreateWapper(请求包装)

         响应：BaseResponse、UserRequest（具体业务响应）

         异步调用：Templete、AbstractTemplete、AsynClientTemplete、CommonListenableCallBack

         请求处理：FutureTpDao

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1、业务标识（使用枚举类来标识业务请求）

          使用枚举类能够比较好地标识具体业务，但是枚举类无法继承，这里通过定义一个空的接口IEnum对其进行抽象。可能看起来会有所不妥，但是也算是一种解决方法吧。

  //空的接口
package acync;

public interface IEnum {
}

  //具体业务标识枚举类，实现了IEnum接口
//
public enum UserEnum implements IEnum {
    ADD,
    UPDATE,
    DELETE,
    MODIFY;
}

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2、请求

          通常情况下，客户端都是发送http请求（使用url的方式）来获取数据，这样，我们主需要获取请求的url地址即可。这里，定义接口BaseRequest提供build方法来构建请求接口，对于具体的业务请求只需实现接口并构建请求url即可。

  //基础请求接口，提供构建URL方法
package acync;

public interface BaseRequest {
    public String build();
}

  //具体的请求类，依据业务情况自行构建URL地址
package acync;

public class UserRequest implements BaseRequest {
    private static final String REQ_URL = "http://www.126.com";

    @Override
    public String build() {
        return REQ_URL;
    }

}

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3、响应

          对于请求响应这里也是定义抽象类BaseResponse，提供status来表示请求的响应状态，而具体的业务响应只需要实现抽象类，自定义实现即可。（其中，BaseResponse抽象类可依据具体的业务框架来定义实现）

  //基础响应抽象类，提供状态码
package acync;

import java.io.Serializable;

public abstract class  BaseResponse implements Serializable{
    private String status;
}

  //具体业务响应类
package acync;

public class UserResponse extends BaseResponse{
//TODO
}

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4、异步调用

          下面的所列代码是整个请求的核心代码。首先，定义模版接口，接口中只提供了若干主要方法，从整体上看，方法的参数为业务请求类和响应类型，返回值为泛型类型的ListenableFuture对象；其次，定义抽象类和具体的实现类；最后，进过请求处理即可获取请求接口。这里不累赘，见下方代码。

  //异步调用模板接口
package acync;

import java.util.Map;

import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.ResponseEntity;
import org.springframework.util.concurrent.ListenableFuture;

public interface Templete {
    <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest, Class<T> responseType) throws Exception;

    <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest,
            ParameterizedTypeReference<T> responseType) throws Exception;

    <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest, Class<T> responseType,
            Map<String, ?> uriVariables) throws Exception;

    <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest,
            ParameterizedTypeReference<T> responseType, Map<String, ?> uriVariables) throws Exception;
}

  //异步调用抽象类
//这里仅仅提供少量的调取方法，可以自行扩展

package acync;

import java.util.Map;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.web.client.AsyncRestTemplate;

public abstract class AbstractTemplete implements Templete{
    public AsyncRestTemplate asyncRestTemplate;

    @Override
    public <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest, Class<T> responseType)
            throws Exception {
        String url = baserequest.build();
        try {
            ListenableFuture<ResponseEntity<T>> t = asyncRestTemplate.getForEntity(url, responseType);
            return t;
        } catch (Exception e) {
            throw e;
        }
    }

    @Override
    public <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest,
            ParameterizedTypeReference<T> responseType) throws Exception {
        String url = baserequest.build();
        try {
            ListenableFuture<ResponseEntity<T>> t = asyncRestTemplate.exchange(url, HttpMethod.GET, null, responseType);
            return t;
        } catch (Exception e) {
            throw e;
        }
    }

    @Override
    public <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest, Class<T> responseType,
            Map<String, ?> uriVariables) throws Exception {
        String url = baserequest.build();
        ListenableFuture<ResponseEntity<T>> t = null;
        try {
            t = asyncRestTemplate.exchange(url, HttpMethod.GET, null, responseType, uriVariables);
            return t;
        } catch (Exception e) {
            throw e;
        }
    }

    @Override
    public <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest,
            ParameterizedTypeReference<T> responseType, Map<String, ?> uriVariables) throws Exception {
        String url = baserequest.build();
        ListenableFuture<ResponseEntity<T>> t = null;
        try {
            t = asyncRestTemplate.exchange(url, HttpMethod.GET, null, responseType, uriVariables);
            return t;
        } catch (Exception e) {
            throw e;
        }
    }

    abstract void setTemplete(AsyncRestTemplate asyncRestTemplate);

}

  // 具体的异步调用实现类
package acync;

import java.util.Map;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.ResponseEntity;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.web.client.AsyncRestTemplate;

public class AsynClientTemplete extends AbstractTemplete {

    public AsynClientTemplete(AsyncRestTemplate template) {
        setTemplete(template);
    }

    public <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest, Class<T> responseType)
            throws Exception {
        return super.getAsyncForObject(baserequest, responseType);
    }

    public <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest,
            ParameterizedTypeReference<T> responseType) throws Exception {
        return super.getAsyncForObject(baserequest, responseType);
    }

    public <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest, Class<T> responseType,
            Map<String, ?> uriVariables) throws Exception {
        return super.getAsyncForObject(baserequest, responseType, uriVariables);
    }

    public <T> ListenableFuture<ResponseEntity<T>> getAsyncForObject(BaseRequest baserequest,
            ParameterizedTypeReference<T> responseType, Map<String, ?> uriVariables) throws Exception {
        return super.getAsyncForObject(baserequest, responseType, uriVariables);
    }

    @Override
    void setTemplete(AsyncRestTemplate template) {
        asyncRestTemplate = template == null ? new AsyncRestTemplate() : template;
    }

}

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5、请求处理

          上述四步都是为这一步做准备。请求处理这一步是请求的入口，在FutureTpDao中，通过getHttpData方法传入请求包装类ConcreateWapper，返回的Map对象Map<即为响应结果，只需依据具体的业务枚举类即可获取对应的业务请求数据。

  //包装了具体的请求信息
//其中的每一个Concreate对应一个具体的请求，baseEnum对应业务标识，variables为请求的额外参数，request为请求类和响应类组成的map

package acync;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class ConcreateWapper {
    private List<Concreate> wrapper = new ArrayList<Concreate>();

    public ConcreateWapper(){}

    public void setParams(IEnum baseEnum, Map<String, ?> variables, Map<BaseRequest, ?> request) {
        wrapper.add(new Concreate(baseEnum, variables, request));
    }

    public List<Concreate> getWrapper() {
        return wrapper;
    }

    public static class Concreate {
        private IEnum baseEnum;
        private Map<String, ?> variables;
        private Map<BaseRequest, ?> request;

        public Concreate(IEnum baseEnum, Map<String, ?> variables, Map<BaseRequest, ?> request) {
            this.baseEnum = baseEnum;
            this.variables = variables;
            this.request = request;
        }

        public IEnum getBaseEnum() {
            return baseEnum;
        }

        public void setBaseEnum(IEnum baseEnum) {
            this.baseEnum = baseEnum;
        }

        public Map<String, ?> getVariables() {
            return variables;
        }

        public void setVariables(Map<String, ?> variables) {
            this.variables = variables;
        }

        public Map<BaseRequest, ?> getRequest() {
            return request;
        }

        public void setRequest(Map<BaseRequest, ?> request) {
            this.request = request;
        }
    }
}

  //实现ListenableFutureCallback，实现回调功能
package acync;

import java.util.Map;
import java.util.concurrent.CountDownLatch;
import org.springframework.http.ResponseEntity;
import org.springframework.util.concurrent.ListenableFutureCallback;


public class CommonListenableCallBack<T> implements ListenableFutureCallback<T> {
    private IEnum type;
    private Map<IEnum, Object> resultValue;
    private volatile CountDownLatch latch;

    public CommonListenableCallBack(IEnum type, Map<IEnum, Object> resultValue, CountDownLatch latch) {
        this.type = type;
        this.resultValue = resultValue;
        this.latch = latch;
    }

    @Override
    public void onSuccess(T result) {
        ResponseEntity<T> re = (ResponseEntity<T>) result;
        if (re != null && re.getBody() != null) {
            T body = re.getBody();
            if (type != null) {
                resultValue.put(type, body);
            }
        }
        latch.countDown();
    }

    @Override
    public void onFailure(Throwable ex) {
        latch.countDown();
    }

}

  //FutureTpDao的构造函数可以传入自定义的AsyncRestTemplate，不传的话就是默认的
//其中的getHttpData()方法传入多个请求的包装类ConcreateWapper，返回数据组成的Map
//其中Map中的key对应的是业务标识，value对应的是请求对应的结果类

package acync;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.web.client.AsyncRestTemplate;
import acync.ConcreateWapper.Concreate;

public class FutureTpDao {
    public AsynClientTemplete asynHttpClient;

    public FutureTpDao(){
        asynHttpClient = new AsynClientTemplete(null);
    }

    public FutureTpDao(AsyncRestTemplate tp) {
        asynHttpClient = new AsynClientTemplete(tp);
    }

    //获取数据
    public Map<IEnum, Object> getHttpData(ConcreateWapper wapper) {
        if (wapper == null)
            return new HashMap<IEnum, Object>();
        final CountDownLatch latch = new CountDownLatch(wapper.getWrapper().size());
        final Map<IEnum, Object> result = new HashMap<IEnum, Object>();

        if (wapper.getWrapper() != null) {
            for (final Concreate wp : wapper.getWrapper()) {
                try {
                    Map<BaseRequest, ?> requestMap = wp.getRequest();
                    for (final BaseRequest tpRequestInfo : requestMap.keySet()) {
                        getHttpdata(wp, tpRequestInfo, latch, requestMap, result);
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }

            try {
                latch.await();
            } catch (Exception e) {
                throw new RuntimeException(e.getMessage());
            }
        }
        return result;
    }

   //发送http请求，获取请求结果
    private void getHttpdata(Concreate wp, BaseRequest tpRequestInfo, CountDownLatch latch,
            Map<BaseRequest, ?> requestMap, Map<IEnum, Object> result) throws Exception {
        ListenableFuture<?> statResponse = null;

        if (requestMap.get(tpRequestInfo) instanceof ParameterizedTypeReference<?>) {
            ParameterizedTypeReference<?> responseType = (ParameterizedTypeReference<?>) requestMap.get(tpRequestInfo);
            statResponse = asynHttpClient.getAsyncForObject(tpRequestInfo, responseType, wp.getVariables());
        } else if (requestMap.get(tpRequestInfo) instanceof Class<?>) {
            Class<?> responseType = (Class<?>) requestMap.get(tpRequestInfo);
            statResponse = asynHttpClient.getAsyncForObject(tpRequestInfo, responseType);
        } else {
            throw new RuntimeException("requestType error...");
        }

        addCallBack(statResponse, wp.getBaseEnum(), latch, result);
    }

    //增加回调
    private <T> void addCallBack(ListenableFuture<T> statResponse, IEnum baseEnum, CountDownLatch latch,
            Map<IEnum, Object> result) {
        if (statResponse != null) {
            statResponse.addCallback(new CommonListenableCallBack<T>(baseEnum, result, latch));
        }
    }
}

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6、示例

  package acync;

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

/**
 * 示例
 * 示例仅仅是一个样板，无法运行
 * 需要在web环境下运行，例如启动tomcat服务器并进行相关配置
 * @author liqqc
 *
 */
public class Demo {

    public static void main(String[] args) {
        ConcreateWapper wapper = new ConcreateWapper();

        Map<BaseRequest, Class<? extends BaseResponse>> request = new HashMap<BaseRequest, Class<? extends BaseResponse>>();
        request.put(new UserRequest(), new UserResponse().getClass());
        wapper.setParams(UserEnum.ADD, null, request);
        wapper.setParams(UserEnum.DELETE, null, request);
        wapper.setParams(UserEnum.UPDATE, null, request);
        wapper.setParams(UserEnum.MODIFY, null, request);

        FutureTpDao futureTpDao = new FutureTpDao();
        Map<IEnum, Object> futureData = futureTpDao.getHttpData(wapper);
        for (IEnum ienum : futureData.keySet()) {
            System.err.println(ienum + "=" + futureData.get(ienum));
        }
    }
}

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Ⅴ、总结

          本文提供了一种基于AsyncRestTemplate来实现批量请求处理的一种方法。整个框架的结构还是比较清晰，由于技术能力有限，若干地方可能考虑有所欠缺，还需进一步深入研究改进。不管怎样，希望本文对你有所帮助。如有疑问可以留言或邮件，谢谢。