總結-HttpClient-RetryHandler重試

目前的項目接口都是http，所以在Java項目中使用apache httpclient進行數據傳輸、訪問。

目前程序中涉及到須要callback操做，product須要被動的接收consume的處理狀態，爲了最大程度的可以callback成功所以consume在http調用出現問題（如：服務不可用、異常、超時）狀況下須要進行重試（retry request），在這裏我列舉出我找到的retry方案，有些成功有些不成功。 我是用的httpclient版本是4.5.2。關於retry功能我在網上也找了很多的資料，可是都不是我對應的httpclient版本，大可能是過期的。 在httpclient版本4.5.2提供瞭如下幾種retry方案：

StandardHttpRequestRetryHandler

 

這種方案沒有測試經過，StandardHttpRequestRetryHandler其實是DefaultHttpRequestRetryHandler的子類，這是官方提供的一個標準的retry方案，爲了保證冪等性約定resetful接口必須是GET, HEAD, PUT, DELETE, OPTIONS, and TRACE中的一種，以下，是我定義的httpclient pool

public static CloseableHttpClient getHttpClient() {
    PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
    cm.setMaxTotal(MAX_TOTAL);
    cm.setDefaultMaxPerRoute(MAX_PERROUTE);
    CloseableHttpClient httpClient = HttpClients
        .custom()
        .setRetryHandler(new StandardHttpRequestRetryHandler())
        .setConnectionManager(cm)
        .build();
    return httpClient;
}

以下是個人測試代碼

@Test
public void test6(){
    HttpPost httpPost=new HttpPost("http://127.0.0.1:8080/testjobs1");
    try {
        rsp=httpClient.execute(httpPost);
        log.info(">> {}",rsp.getStatusLine().getStatusCode());
    } catch (Exception e) {
        log.error(e.getMessage(),e);
    }finally{
        HttpUtil.close(rsp);
    }
}

運行測試，當url錯誤、後臺報錯、後臺超時等狀況的時候不能進行retry，所以放棄了此方案。

DefaultHttpRequestRetryHandler

這種方案沒有測試經過，和上面的StandardHttpRequestRetryHandler相似，它提供了一種默認的retry方案，並無像StandardHttpRequestRetryHandler同樣約定接口必須是冥等的，以下，是我定義的httpclient pool

public static CloseableHttpClient getHttpClient() {
    PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
    cm.setMaxTotal(MAX_TOTAL);
    cm.setDefaultMaxPerRoute(MAX_PERROUTE);
    CloseableHttpClient httpClient = HttpClients
        .custom()
        .setRetryHandler(new DefaultHttpRequestRetryHandler())
        .setConnectionManager(cm)
        .build();
    return httpClient;
}

以下是個人測試代碼

@Test
public void test6(){
    HttpPost httpPost=new HttpPost("http://127.0.0.1:8080/testjobs1");
    try {
        rsp=httpClient.execute(httpPost);
        log.info(">> {}",rsp.getStatusLine().getStatusCode());
    } catch (Exception e) {
        log.error(e.getMessage(),e);
    }finally{
        HttpUtil.close(rsp);
    }
}

依然沒有達到但願的效果。

HttpRequestRetryHandler

能夠實現，可是不夠完美。在官方文檔有這麼一段，以下，

HttpRequestRetryHandler myRetryHandler = new HttpRequestRetryHandler() {
    public boolean retryRequest(
        IOException exception,
        int executionCount,
        HttpContext context) {
        if (executionCount >= 5) {
            // Do not retry if over max retry count
            return false;
        }
        if (exception instanceof InterruptedIOException) {
            // Timeout
            return false;
        }
        if (exception instanceof UnknownHostException) {
            // Unknown host
            return false;
        }
        if (exception instanceof ConnectTimeoutException) {
            // 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 httpclient = HttpClients.custom().setRetryHandler(myRetryHandler).build();

自定義retry實現，這比較靈活，能夠根據異常自定義retry機制以及重試次數，而且能夠拿到返回信息，以下，是我定義的httpclient pool

public static CloseableHttpClient getHttpClient() {
    HttpRequestRetryHandler retryHandler = new HttpRequestRetryHandler() {
        public boolean retryRequest(
            IOException exception,
            int executionCount,
            HttpContext context) {
            if (executionCount >= 5) {
                // Do not retry if over max retry count
                return false;
            }
            if (exception instanceof InterruptedIOException) {
                // Timeout
                return false;
            }
            if (exception instanceof UnknownHostException) {
                // Unknown host
                return false;
            }
            if (exception instanceof ConnectTimeoutException) {
                // 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;
        }
    };
    PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
    cm.setMaxTotal(MAX_TOTAL);
    cm.setDefaultMaxPerRoute(MAX_PERROUTE);
    CloseableHttpClient httpClient = HttpClients
        .custom()
        .setRetryHandler(retryHandler)
        .setConnectionManager(cm)
        .build();
    return httpClient;
}

以下是個人測試代碼

@Test
public void test6(){
    HttpPost httpPost=new HttpPost("http://127.0.0.1:8080/testjobs1");
    try {
        rsp=httpClient.execute(httpPost);
        log.info(">> {}",rsp.getStatusLine().getStatusCode());
    } catch (Exception e) {
        log.error(e.getMessage(),e);
    }finally{
        HttpUtil.close(rsp);
    }
}

這種方案，能夠實現retry，而且能夠根據個人需求進行retry，如：retry count，可是就不能控制retry時間的間隔，也只好放棄了，繼續尋找找到了下面這個ServiceUnavailableRetryStrategy。

ServiceUnavailableRetryStrategy

能夠實現，知足需求，這具備HttpRequestRetryHandler的全部有點，而且能夠自定義retry時間的間隔，以下，是我定義的httpclient pool，

public static CloseableHttpClient getHttpClient() {
    ServiceUnavailableRetryStrategy serviceUnavailableRetryStrategy = new ServiceUnavailableRetryStrategy() {
        /**
         * retry邏輯
         */
        @Override
        public boolean retryRequest(HttpResponse response, int executionCount, HttpContext context) {
            if (executionCount <= 3)
                return true;
            else
                return false;
        }
        /**
         * retry間隔時間
         */
        @Override
        public long getRetryInterval() {
            return 2000;
        }
    };
    PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
    cm.setMaxTotal(MAX_TOTAL);
    cm.setDefaultMaxPerRoute(MAX_PERROUTE);
    CloseableHttpClient httpClient = HttpClients.custom().setRetryHandler(new DefaultHttpRequestRetryHandler())
        .setConnectionManager(cm).build();
    return httpClient;
}

以下是個人測試代碼

@Test
public void test6(){
    HttpPost httpPost=new HttpPost("http://127.0.0.1:8080/testjobs1");
    try {
        rsp=httpClient.execute(httpPost);
        log.info(">> {}",rsp.getStatusLine().getStatusCode());
    } catch (Exception e) {
        log.error(e.getMessage(),e);
    }finally{
        HttpUtil.close(rsp);
}
}