前段时间有个需求在springmvc mapping的url跳转前完成一个统计的业务。显然需要进行异步的处理,不然出错或者异常会影响到后面的网页跳转。异步的方式也就是非阻塞式的,当异步调用成功与否程序会接着往下执行,不必等到输入输出处理完毕才返回。
主要用到httpasyncclient-4.0.1.jar,httpclient-4.3.2.jar,httpcore-4.3.2.jar,httpcore-nio-4.3.2.jar,commons-logging-1.1.3.jar。
java.util.concurrent中主要包括三类工具,Executor Freamework,并发集合(Concurrent Collection),以及同步器(Synchronizer)。下面的例子是利用java.util.concurrent.Future只请求一个url异步请求。Future接口表示异步计算的结果。它提供了检查计算是否完成的方法,以等待计算的完成,并获取计算的结果。计算完成后只能使用 get 方法来获取结果,如有必要,计算完成前可以阻塞此方法。取消则由 cancel 方法来执行。还提供了其他方法,以确定任务是正常完成还是被取消了。一旦计算完成,就不能再取消计算。如果为了可取消性而使用 Future 但又不提供可用的结果,则可以声明 Future> 形式类型、并返回 null 作为底层任务的结果。
import java.util.concurrent.Future;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.nio.client.CloseableHttpAsyncClient;
import org.apache.http.impl.nio.client.HttpAsyncClients;
/**
* This example demonstrates a basic asynchronous HTTP request / response
* exchange. Response content is buffered in memory for simplicity.
*/
public class AsyncClientHttpExchange {
public static void main(final String[] args) throws Exception {
CloseableHttpAsyncClient httpclient = HttpAsyncClients.createDefault();// 默认的配置
try {
httpclient.start();
HttpGet request = new HttpGet("http://www.apache.org/");
Future future = httpclient.execute(request, null);
HttpResponse response = future.get();// 获取结果
System.out.println("Response: " + response.getStatusLine());
System.out.println("Shutting down");
} finally {
httpclient.close();
}
System.out.println("Done");
}
}
import java.util.concurrent.CountDownLatch;
import org.apache.http.HttpResponse;
import org.apache.http.client.config.RequestConfig;
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;
/**
* This example demonstrates a fully asynchronous execution of multiple HTTP
* exchanges where the result of an individual operation is reported using a
* callback interface.
*/
public class AsyncClientHttpExchangeFutureCallback {
public static void main(final String[] args) throws Exception {
RequestConfig requestConfig = RequestConfig.custom()
.setSocketTimeout(3000).setConnectTimeout(3000).build();
CloseableHttpAsyncClient httpclient = HttpAsyncClients.custom()
.setDefaultRequestConfig(requestConfig).build();
try {
httpclient.start();
final HttpGet[] requests = new HttpGet[] {
new HttpGet("http://www.apache.org/"),
new HttpGet("https://www.verisign.com/"),
new HttpGet("http://www.google.com/"),
new HttpGet("http://www.baidu.com/") };
final CountDownLatch latch = new CountDownLatch(requests.length);
for (final HttpGet request : requests) {
httpclient.execute(request, new FutureCallback() {
//无论完成还是失败都调用countDown()
@Override
public void completed(final HttpResponse response) {
latch.countDown();
System.out.println(request.getRequestLine() + "->"
+ response.getStatusLine());
}
@Override
public void failed(final Exception ex) {
latch.countDown();
System.out.println(request.getRequestLine() + "->" + ex);
}
@Override
public void cancelled() {
latch.countDown();
System.out.println(request.getRequestLine()
+ " cancelled");
}
});
}
latch.await();
System.out.println("Shutting down");
} finally {
httpclient.close();
}
System.out.println("Done");
}
}