异步httpclient(httpasyncclient)的使用与总结

Posted 2021-02-06 aspirant

参考：异步httpclient(httpasyncclient)的使用与总结

1. 前言
应用层的网络模型有同步与异步。同步意味当前线程是阻塞的，只有本次请求完成后才能进行下一次请求;异步意味着所有的请求可以同时塞入缓冲区,不阻塞当前的线程;

httpclient在4.x之后开始提供基于nio的异步版本httpasyncclient,httpasyncclient借助了Java并发库和nio进行封装(虽说NIO是同步非阻塞IO,但是HttpAsyncClient提供了回调的机制,与netty类似,所以可以模拟类似于AIO的效果),其调用方式非常便捷,但是其中也有许多需要注意的地方。

2. pom文件
本文依赖4.1.2,当前最新的客户端版本是4.1.3maven repository 地址

<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
<version>4.5.2</version>
</dependency>

<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpcore</artifactId>
<version>4.4.5</version>
</dependency>

<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpcore-nio</artifactId>
<version>4.4.5</version>
</dependency>

<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpasyncclient</artifactId>
<version>4.1.2</version>
</dependency>
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3. 简单的实例
public class TestHttpClient {
public static void main(String[] args){

RequestConfig requestConfig = RequestConfig.custom()
.setConnectTimeout(50000)
.setSocketTimeout(50000)
.setConnectionRequestTimeout(1000)
.build();

//配置io线程
IOReactorConfig ioReactorConfig = IOReactorConfig.custom().
setIoThreadCount(Runtime.getRuntime().availableProcessors())
.setSoKeepAlive(true)
.build();
//设置连接池大小
ConnectingIOReactor ioReactor=null;
try {
ioReactor = new DefaultConnectingIOReactor(ioReactorConfig);
} catch (IOReactorException e) {
e.printStackTrace();
}
PoolingNHttpClientConnectionManager connManager = new PoolingNHttpClientConnectionManager(ioReactor);
connManager.setMaxTotal(100);
connManager.setDefaultMaxPerRoute(100);

final CloseableHttpAsyncClient client = HttpAsyncClients.custom().
setConnectionManager(connManager)
.setDefaultRequestConfig(requestConfig)
.build();

//构造请求
String url = "http://127.0.0.1:9200/_bulk";
HttpPost httpPost = new HttpPost(url);
StringEntity entity = null;
try {
String a = "{ "index": { "_index": "test", "_type": "test"} } " +
"{"name": "上海","age":33} ";
entity = new StringEntity(a);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
httpPost.setEntity(entity);

//start
client.start();

//异步请求
client.execute(httpPost, new Back());

while(true){
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

static class Back implements FutureCallback<HttpResponse>{

private long start = System.currentTimeMillis();
Back(){
}

public void completed(HttpResponse httpResponse) {
try {
System.out.println("cost is:"+(System.currentTimeMillis()-start)+":"+EntityUtils.toString(httpResponse.getEntity()));
} catch (IOException e) {
e.printStackTrace();
}
}

public void failed(Exception e) {
System.err.println(" cost is:"+(System.currentTimeMillis()-start)+":"+e);
}

public void cancelled() {

}
}
}
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4. 几个重要的参数
4.1 TimeOut(3个)的设置

ConnectTimeout : 连接超时,连接建立时间,三次握手完成时间。
SocketTimeout : 请求超时,数据传输过程中数据包之间间隔的最大时间。
ConnectionRequestTimeout : 使用连接池来管理连接,从连接池获取连接的超时时间。

在实际项目开发过程中,这三个值可根据具体情况设置。

(1) 下面针对ConnectionRequestTimeout的情况进行分析

实验条件:设置连接池最大连接数为1,每一个异步请求从开始到回调的执行时间在100ms以上;

实验过程:连续发送2次请求

public class TestHttpClient {
public static void main(String[] args){

RequestConfig requestConfig = RequestConfig.custom()
.setConnectTimeout(50000)
.setSocketTimeout(50000)
.setConnectionRequestTimeout(10)//设置为10ms
.build();

//配置io线程
IOReactorConfig ioReactorConfig = IOReactorConfig.custom().
setIoThreadCount(Runtime.getRuntime().availableProcessors())
.setSoKeepAlive(true)
.build();
//设置连接池大小
ConnectingIOReactor ioReactor=null;
try {
ioReactor = new DefaultConnectingIOReactor(ioReactorConfig);
} catch (IOReactorException e) {
e.printStackTrace();
}
PoolingNHttpClientConnectionManager connManager = new PoolingNHttpClientConnectionManager(ioReactor);
connManager.setMaxTotal(1);//最大连接数设置1
connManager.setDefaultMaxPerRoute(1);//per route最大连接数设置1

final CloseableHttpAsyncClient client = HttpAsyncClients.custom().
setConnectionManager(connManager)
.setDefaultRequestConfig(requestConfig)
.build();

//构造请求
String url = "http://127.0.0.1:9200/_bulk";
List<HttpPost> list = new ArrayList<HttpPost>();
for(int i=0;i<2;i++){
HttpPost httpPost = new HttpPost(url);
StringEntity entity = null;
try {
String a = "{ "index": { "_index": "test", "_type": "test"} } " +
"{"name": "上海","age":33} ";
entity = new StringEntity(a);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
httpPost.setEntity(entity);
list.add(httpPost);
}

client.start();

for(int i=0;i<2;i++){
client.execute(list.get(i), new Back());
}

while(true){
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

static class Back implements FutureCallback<HttpResponse>{

private long start = System.currentTimeMillis();
Back(){
}

public void completed(HttpResponse httpResponse) {
try {
System.out.println("cost is:"+(System.currentTimeMillis()-start)+":"+EntityUtils.toString(httpResponse.getEntity()));
} catch (IOException e) {
e.printStackTrace();
}
}

public void failed(Exception e) {
e.printStackTrace();
System.err.println(" cost is:"+(System.currentTimeMillis()-start)+":"+e);
}

public void cancelled() {

}
}
}
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实验结果 :
第一次请求执行时间在200ms左右
第二请求回调直接抛出TimeOutException

java.util.concurrent.TimeoutException
at org.apache.http.nio.pool.AbstractNIOConnPool.processPendingRequest(AbstractNIOConnPool.java:364)
at org.apache.http.nio.pool.AbstractNIOConnPool.processNextPendingRequest(AbstractNIOConnPool.java:344)
at org.apache.http.nio.pool.AbstractNIOConnPool.release(AbstractNIOConnPool.java:318)
at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.releaseConnection(PoolingNHttpClientConnectionManager.java:303)
at org.apache.http.impl.nio.client.AbstractClientExchangeHandler.releaseConnection(AbstractClientExchangeHandler.java:239)
at org.apache.http.impl.nio.client.MainClientExec.responseCompleted(MainClientExec.java:387)
at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.responseCompleted(DefaultClientExchangeHandlerImpl.java:168)
at org.apache.http.nio.protocol.HttpAsyncRequestExecutor.processResponse(HttpAsyncRequestExecutor.java:436)
at org.apache.http.nio.protocol.HttpAsyncRequestExecutor.inputReady(HttpAsyncRequestExecutor.java:326)
at org.apache.http.impl.nio.DefaultNHttpClientConnection.consumeInput(DefaultNHttpClientConnection.java:265)
at org.apache.http.impl.nio.client.InternalIODispatch.onInputReady(InternalIODispatch.java:81)
at org.apache.http.impl.nio.client.InternalIODispatch.onInputReady(InternalIODispatch.java:39)
at org.apache.http.impl.nio.reactor.AbstractIODispatch.inputReady(AbstractIODispatch.java:114)
at org.apache.http.impl.nio.reactor.BaseIOReactor.readable(BaseIOReactor.java:162)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvent(AbstractIOReactor.java:337)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvents(AbstractIOReactor.java:315)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.execute(AbstractIOReactor.java:276)
at org.apache.http.impl.nio.reactor.BaseIOReactor.execute(BaseIOReactor.java:104)
at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor$Worker.run(AbstractMultiworkerIOReactor.java:588)
at java.lang.Thread.run(Thread.java:745)
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结果分析：由于连接池大小是1,第一次请求执行后连接被占用(时间在100ms),第二次请求在规定的时间内无法获取连接,于是直接连接获取的TimeOutException

(2) 修改ConnectionRequestTimeout

RequestConfig requestConfig = RequestConfig.custom()
.setConnectTimeout(50000)
.setSocketTimeout(50000)
.setConnectionRequestTimeout(1000)//设置为1000ms
.build();
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上述两次请求正常执行。

下面进一步看一下代码中抛异常的地方：

 

 

从上面的代码中可以看到如果要设置永不ConnectionRequestTimeout，只需要将ConnectionRequestTimeout设置为小于0即可,当然后这种设置一定要慎用, 如果处理不当,请求堆积会导致OOM。

4.2 连接池大小的设置

ConnTotal:连接池中最大连接数;
ConnPerRoute(1000):分配给同一个route(路由)最大的并发连接数,route为运行环境机器到目标机器的一条线路,举例来说,我们使用HttpClient的实现来分别请求 www.baidu.com 的资源和 www.bing.com 的资源那么他就会产生两个route;

对于上述的实验,在一定程度上可以通过增大最大连接数来解决ConnectionRequestTimeout的问题！

后续：本文重点在于使用，后续会对源码进行分析与解读

下载地址：http://hc.apache.org/downloads.cgi

在NetBeans中导入以下jar文件：

1：一次请求：

 public static void oneReuest(){
        final CloseableHttpAsyncClient httpClient = HttpAsyncClients.createDefault();
        httpClient.start();
        final HttpGet request = new HttpGet("http://www.apache.org/");
        final Future future = httpClient.execute(request, null);
        try {
            HttpResponse response = (HttpResponse) future.get();
            System.out.println("Response:" + response.getStatusLine());
            System.out.println("Shutting down");
        } catch (Exception ex) {
            Logger.getLogger(Httpasyncclient.class.getName()).log(Level.SEVERE, null, ex);
        }finally{
            try {
                httpClient.close();
            } catch (IOException ex) {
                Logger.getLogger(Httpasyncclient.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        
        System.out.println("执行完毕");
    }

2：多次异步请求：

 public static void moreRequest(){
        final RequestConfig requestConfitg = RequestConfig.custom()
                .setSocketTimeout(3000)
                .setConnectTimeout(3000).build();
        
        final CloseableHttpAsyncClient httpClient = HttpAsyncClients.custom()
                .setDefaultRequestConfig(requestConfitg)
                .build();
        
        httpClient.start();
        
        final HttpGet[] requests = new HttpGet[]{
            new HttpGet("http://www.apache.org/"),
            new HttpGet("http://www.baidu.com/"),
            new HttpGet("http://www.oschina.net/")
        };
        
        final CountDownLatch latch = new CountDownLatch(requests.length);
        for(final HttpGet request: requests){
            
                httpClient.execute(request, new FutureCallback(){
                    @Override
                    public void completed(Object obj) {
                       final HttpResponse response = (HttpResponse)obj;
                       latch.countDown();
                       System.out.println(request.getRequestLine() + "->" + response.getStatusLine());
                    }

                    @Override
                    public void failed(Exception excptn) {
                        latch.countDown();
                        System.out.println(request.getRequestLine() + "->" + excptn);
                    }

                    @Override
                    public void cancelled() {
                        latch.countDown();
                        System.out.println(request.getRequestLine() + "cancelled");
                    }
                });
         }       
        
        try {
            latch.await();
            System.out.println("Shutting Down");
        } catch (InterruptedException ex) {
            Logger.getLogger(Httpasyncclient.class.getName()).log(Level.SEVERE, null, ex);
        }finally{
            try {
                httpClient.close();
            } catch (IOException ex) {
                Logger.getLogger(Httpasyncclient.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        System.out.println("Finish!");
    }

运行结果：

run:
GET http://www.baidu.com/ HTTP/1.1->HTTP/1.1 200 OK
GET http://www.oschina.net/ HTTP/1.1->HTTP/1.1 200 OK
GET http://www.apache.org/ HTTP/1.1->HTTP/1.1 200 OK
Shutting Down
Finish!
成功构建 (总时间: 2 秒)

可以看出是异步执行的！不是按照我们传入的URL参数顺序执行的！

 

篇提到了高性能处理的关键是异步，而我们当中许多人依旧在使用同步模式的HttpClient访问第三方Web资源，我认为原因之一是：异步的HttpClient诞生较晚，许多人不知道；另外也可能是大多数Web程序其实不在意这点性能损失了。

而要自己实现一个异步的HttpClient则比较困难，通常都是自己开一个新的工作线程，利用HttpClient的同步去访问，完成后再回调这种形式，这样做其实不是真正的异步，因为依旧会有一个线程处于阻塞中，等待着第三方Web资源的返回。

而如今访问第三方Web资源的情景越来越多，最典型就是使用第三方登录平台，如QQ或微信等，我们需要访问腾讯的服务器去验证登录者的身份，根据我的经验，这个过程可能会阻塞好几秒钟，可看作是一个“长时间调用”，所以最好要使用异步方式。

OK，废话少说，要使用异步的HttpClient，请Maven中带上：

        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpasyncclient</artifactId>
            <version>4.1.1</version>
        </dependency>

接下来是一个完整的Demo代码：

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.concurrent.FutureCallback;
import org.apache.http.impl.nio.client.CloseableHttpAsyncClient;
import org.apache.http.impl.nio.client.HttpAsyncClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;
import java.util.concurrent.CountDownLatch;

public class Main {
    public static void main(String[] argv) {
        CloseableHttpAsyncClient httpclient = HttpAsyncClients.createDefault();
        httpclient.start();

        final CountDownLatch latch = new CountDownLatch(1);
        final HttpGet request = new HttpGet("https://www.alipay.com/");

        System.out.println(" caller thread id is : " + Thread.currentThread().getId());

        httpclient.execute(request, new FutureCallback<HttpResponse>() {

            public void completed(final HttpResponse response) {
                latch.countDown();
                System.out.println(" callback thread id is : " + Thread.currentThread().getId());
                System.out.println(request.getRequestLine() + "->" + response.getStatusLine());
                try {
                    String content = EntityUtils.toString(response.getEntity(), "UTF-8");
                    System.out.println(" response content is : " + content);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            public void failed(final Exception ex) {
                latch.countDown();
                System.out.println(request.getRequestLine() + "->" + ex);
                System.out.println(" callback thread id is : " + Thread.currentThread().getId());
            }

            public void cancelled() {
                latch.countDown();
                System.out.println(request.getRequestLine() + " cancelled");
                System.out.println(" callback thread id is : " + Thread.currentThread().getId());
            }

        });
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        try {
            httpclient.close();
        } catch (IOException ignore) {

        }
    }
}

 呃……代码很简单，好像也没什么好说的了，稍作封装就可以实现如“getJson()”这样的方法。

也许你还注意到了，这个HttpClient跟同步的版本一样，直接支持https，但如果网站的证书是自签的，默认还是不行的，解决方法当然有，但代码有些麻烦，我觉得还不如直接买张证书来得简单，如果网站是你管的话。

参考：Java的异步HttpClient

参考：HttpAsyncClient 的简单使用