Question

我有以下方法，它使用代理从服务器检索信息。有时由于代理不当，我会收到SocketException，SSLException，SSLHandshakeException或ConnectException

正如您在我的方法中所看到的，我已经在使用catch (IOException ioe)我需要这样做，以便在服务器返回除代码200之外的任何内容时获取服务器响应的内容。

如果出现上述异常，如何重试方法？

public String getMeta() throws IOException
{

    HttpsURLConnection con = null;
    InputStream is = null;
    StringWriter writer = new StringWriter();
    try
    {
        String url = "https://api.myapp.com/meta";
        URL urlObj = new URL(url);

        if (useProxy && fullProxy)
        {
            myapp.Proxy proxyCustom = getRandomProxy();
            Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(proxyCustom.getProxyIp(), proxyCustom.getProxyPort()));
            con = (HttpsURLConnection) urlObj.openConnection(proxy);
        }
        else
        {
            con = (HttpsURLConnection) urlObj.openConnection();
        }

        con.setRequestMethod("GET");
        con.setRequestProperty("User-Agent", USER_AGENT);
        con.setRequestProperty("Content-Type", "application/json; charset=utf-8");
        con.setRequestProperty("host", urlObj.getHost());
        con.setRequestProperty("Connection", "Keep-Alive");

        int responseCode = 0;

        responseCode = con.getResponseCode();

        is = con.getInputStream();
        writer = new StringWriter();
        IOUtils.copy(is, writer, "UTF-8");
    }
    catch (IOException ioe)
    {
        if (con instanceof HttpsURLConnection)
        {
            HttpsURLConnection httpConn = (HttpsURLConnection) con;
            int statusCode = httpConn.getResponseCode();
            if (statusCode != 200)
            {
                is = httpConn.getErrorStream();
                writer = new StringWriter();
                IOUtils.copy(is, writer, "UTF-8");
            }
        }
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }

    return writer.toString();
}

Answer 1

我将采用的方法是创建一个新的重试方法，并在getMeta（）方法结束时调用它，以便在出现异常时调用它我假设您应该只调用几次重试，因此getMeta应该在一定次数之后抛出一些异常，如RetryException

public String getMeta() throws IOException, RetryException
{

    HttpsURLConnection con = null;
    InputStream is = null;
    StringWriter writer = new StringWriter();
    try
    {
        String url = "https://api.myapp.com/meta";
        URL urlObj = new URL(url);

        if (useProxy && fullProxy)
        {
            myapp.Proxy proxyCustom = getRandomProxy();
            Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(proxyCustom.getProxyIp(), proxyCustom.getProxyPort()));
            con = (HttpsURLConnection) urlObj.openConnection(proxy);
        }
        else
        {
            con = (HttpsURLConnection) urlObj.openConnection();
        }

        con.setRequestMethod("GET");
        con.setRequestProperty("User-Agent", USER_AGENT);
        con.setRequestProperty("Content-Type", "application/json; charset=utf-8");
        con.setRequestProperty("host", urlObj.getHost());
        con.setRequestProperty("Connection", "Keep-Alive");

        int responseCode = 0;

        responseCode = con.getResponseCode();

        is = con.getInputStream();
        writer = new StringWriter();
        IOUtils.copy(is, writer, "UTF-8");

        return writer.toString();
    }
    catch (IOException ioe)
    {
        if (con instanceof HttpsURLConnection)
        {
            HttpsURLConnection httpConn = (HttpsURLConnection) con;
            int statusCode = httpConn.getResponseCode();
            if (statusCode != 200)
            {
                is = httpConn.getErrorStream();
                writer = new StringWriter();
                IOUtils.copy(is, writer, "UTF-8");

                return writer.toString();
            }
        }
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }

    return retryGetMeta();
}


private String retryGetMeta()
{
   try
   {
       return getMeta();
   }
   finally
   {
       //Do your stuff
   }
}

public RetryException extends Exception
{
    private   String message =  "Retries exceeded";

      public String getMessage()
      {
         return message;
      }

}

如果你的getMeta（）中抛出异常，catch会像你现在那样做它的东西，但之后，将调用retryGetMeta

Answer 2

如果出现上述异常，如何重试方法？

下面显示的一种方法是让getMeta方法实际抛出IOException。然后，由于任何捕获的异常，您可以使用caller方法递归调用自身。

我希望有一种简单的方法来设置它应该重试的次数

为了能够多次调用方法n，将次数作为参数传递，并相应地处理停止标准逻辑。例如：

public String caller(int total) throws IOException{
    return callerImpl(1, total);
}

public String callerImpl(int current, int total) throws IOException{
    try{
        return getMeta();
    }catch(IOException e){
        current++;
        if ( current > total ){
            throw e;//or return null or empty string, depending upon upstream requirements
        }
        return callerImpl(current, total);
    }

    return null;
}

在getMeta中：

try{
    ....
}catch(IOException io){
    //log or handle io
    throw io;
}

注意，上面没有涉及抛出异常的日志/逻辑，您可能希望以某种方式处理它们。

重试某些例外的方法

2 个答案: