使用Apache HttpClient 4.x进行异常重试

在进行http请求时，难免会遇到请求失败的情况，失败后需要重新请求，尝试再次获取数据。

Apache的HttpClient提供了异常重试机制，在该机制中，我们可以很灵活的定义在哪些异常情况下进行重试。

重试前提

被请求的方法必须是幂等的：就是多次请求服务端结果应该是准确且一致的。 

适合的方法：比如根据ID，修改人员姓名，无论请求多次结果都是一样，这就是幂等。 

不适合的方法：比如减少账号50元，多次请求将多次扣减。

实现方式

想要实现异常重试，需要实现它提供的一个接口  HttpRequestRetryHandler ，并实现 retryRequest 方法。然后set到HttpClient中。该httpClient就具备了重试机制。

 

HttpClient自身提供了 StandardHttpRequestRetryHandler 和 DefaultHttpRequestRetryHandler 两个实现类。 DefaultHttpRequestRetryHandler 继承自 DefaultHttpRequestRetryHandler ， StandardHttpRequestRetryHandler 默认几个方法为幂等，如PUT、GET、HEAD等除POST外的方法，如果自定义可以参考它的实现方式。

 

代码如下：

import java.io.IOException;
import java.io.InterruptedIOException;
import java.net.ConnectException;
import java.net.UnknownHostException;

import javax.net.ssl.SSLException;

import org.apache.commons.lang3.ObjectUtils;
import org.apache.commons.lang3.StringUtils;
import org.apache.http.Consts;
import org.apache.http.HttpEntityEnclosingRequest;
import org.apache.http.HttpRequest;
import org.apache.http.HttpStatus;
import org.apache.http.ParseException;
import org.apache.http.client.HttpRequestRetryHandler;
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.client.protocol.HttpClientContext;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.protocol.HttpContext;
import org.apache.http.util.EntityUtils;

/**
 * @author 29  *
 * @date 2017年5月18日 上午9:17:30
 *
 * @Description
 */
public class HttpPostUtils {
    /**
     * 
     * @param uri
     *            the request address
     * @param json
     *            the request data that must be a JSON string
     * @param retryCount
     *            the number of times this method has been unsuccessfully
     *            executed
     * @param connectTimeout
     *            the timeout in milliseconds until a connection is established
     * @param connectionRequestTimeout
     *            the timeout in milliseconds used when requesting a connection
     *            from the connection manager
     * @param socketTimeout
     *            the socket timeout in milliseconds, which is the timeout for
     *            waiting for data or, put differently, a maximum period
     *            inactivity between two consecutive data packets
     * @return null when method parameter is null, "", " "
     * @throws IOException
     *             if HTTP connection can not opened or closed successfully
     * @throws ParseException
     *             if response data can not be parsed successfully
     */
    public String retryPostJson(String uri, String json, int retryCount, int connectTimeout,
            int connectionRequestTimeout, int socketTimeout) throws IOException, ParseException {
        if (StringUtils.isAnyBlank(uri, json)) {
            return null;
        }

        HttpRequestRetryHandler httpRequestRetryHandler = new HttpRequestRetryHandler() {

            @Override
            public boolean retryRequest(IOException exception, int executionCount, HttpContext context) {
                if (executionCount > retryCount) {
                    // Do not retry if over max retry count
                    return false;
                }
                if (exception instanceof InterruptedIOException) {
                    // An input or output transfer has been terminated
                    return false;
                }
                if (exception instanceof UnknownHostException) {
                    // Unknown host 修改代码让不识别主机时重试，实际业务当不识别的时候不应该重试，再次为了演示重试过程，执行会显示retryCount次下面的输出
                    System.out.println("不识别主机重试"); return true;
                }
                if (exception instanceof ConnectException) {
                    // Connection refused
                    return false;
                }
                if (exception instanceof SSLException) {
                    // SSL handshake exception
                    return false;
                }
                HttpClientContext clientContext = HttpClientContext.adapt(context);
                HttpRequest request = clientContext.getRequest();
                boolean idempotent = !(request instanceof HttpEntityEnclosingRequest);
                if (idempotent) {
                    // Retry if the request is considered idempotent
                    return true;
                }
                return false;
            }
        };

        CloseableHttpClient client = HttpClients.custom().setRetryHandler(httpRequestRetryHandler).build();
        HttpPost post = new HttpPost(uri);
        // Create request data
        StringEntity entity = new StringEntity(json, ContentType.APPLICATION_JSON);
        // Set request body
        post.setEntity(entity);

        RequestConfig config = RequestConfig.custom().setConnectTimeout(connectTimeout)
                .setConnectionRequestTimeout(connectionRequestTimeout).setSocketTimeout(socketTimeout).build();
        post.setConfig(config);
        // Response content
        String responseContent = null;
        CloseableHttpResponse response = null;
        try {
            response = client.execute(post, HttpClientContext.create());
            if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                responseContent = EntityUtils.toString(response.getEntity(), Consts.UTF_8.name());
            }
        } finally {
            if (ObjectUtils.anyNotNull(response)) {
                response.close();
            }
            if (ObjectUtils.anyNotNull(client)) {
                client.close();
            }
        }
        return responseContent;
    }

 

转载自：http://www.cnblogs.com/wuxiaofeng/p/6879292.html，感谢分享。