在Java中嵌套try / catch語句是否可以接受？

Question

我試圖從傳入的值（使用Bundle）在Android中創建一個IP地址，如果失敗，我將使用硬編碼的默認IP地址創建它。 如果失敗，那么我退出應用程序。

我想知道的是，如果可以像我在這里做的那樣嵌套try / catch，或者是否有更好的方法。

try {
    // serverSettings is the Bundle name that was passed in.
    ipAddress = InetAddress.getByName(serverSettings.getString("serverIp"));
} catch (UnknownHostException e) {
    Log.e("ERROR:", "IOException: Failed to create IP, trying default");
    try {
        // DEFAULT_IP is the hard-coded default fall-back address
        ipAddress = InetAddress.getByName(DEFAULT_IP);
    } catch (UnknownHostException e1) {
        Log.e("ERROR:", "IOException: Total fail, exiting");
        e1.printStackTrace();
        finish();
    }
}

Answer 1

這是合法的Java。 它看起來很笨我，我可能會采用不同的方式，但它有效並且有效。

這是我如何做到的：

public InetAddress getServerAddress() {
    for (String address : new String[] {serverSettings.getString("serverIp"), DEFAULT_IP}) {
        try {
            return InetAddress.getByName(address);
        } catch (UnknownHostException e) {
            Log.e("ERROR:", "Cannot resolve " + address);
        }
    }
    Log.e("ERROR:", "Total fail, exiting");
    finish();
    return null;    // not reached
}

Answer 2

我認為這將是有爭議的更好的方式，但這是另一種選擇，有些人可能認為更具“表現力”和可讀性，雖然它是更多的代碼行：

public InetAddress tryHost(String hostName) {
    InetAddress address = null;
    try {
        address = InetAddress.getByName(hostName);
    } catch (UnknownHostException e) {
        e.printStackTrace();
    }
    return null;
}

然后在你的代碼中，只需：

InetAddress address = null;
address = tryHost(serverSettings.getString("serverIp"));
if (address = null)
    address = tryHost(DEFAULT_IP);
if (address = null) {
    // handle error, throw exception
}
finish();

Answer 3

另一種變體是首先設置默認值：

ipAddress = null;
try {
    // serverSettings is the Bundle name that was passed in.
    ipAddress = InetAddress.getByName(DEFAULT_IP); // Set default address
    ipAddress = InetAddress.getByName(serverSettings.getString("serverIp")); // Try passed-in address
} catch (UnknownHostException e) {
    if (ipAddress == null) {
        Log.e("ERROR:", "IOException: Total fail, exiting");
        e1.printStackTrace();
        finish();
    }
}

如果使用Bundle'd值的調用失敗，則在修改ipAddress之前拋出異常，因此ipAddress已設置為默認值。 當然，如果DEFAULT_IP始終可以解析，這只是一個有效的模式。

Answer 4

沒關系。 您還可以使用在第一個catch中打開的布爾標志，因此如果您的布爾標志打開，則在catch外部通過IP執行請求。

boolean failed = false;
try {
    // serverSettings is the Bundle name that was passed in.
    ipAddress = InetAddress.getByName(serverSettings.getString("serverIp"));
} catch (UnknownHostException e) {
    failed = true;
    Log.e("ERROR:", "IOException: Failed to create IP, trying default");    
}

if(failed){
    try {
            // DEFAULT_IP is the hard-coded default fall-back address
            ipAddress = InetAddress.getByName(DEFAULT_IP);
        } catch (UnknownHostException e1) {
            Log.e("ERROR:", "IOException: Total fail, exiting");
            e1.printStackTrace();
            finish();
        }
    }
}

Answer 5

我更喜歡這個。 它有點清潔，不涉及額外的標志。

InetAddress ipAddress = null;
try {
    // serverSettings is the Bundle name that was passed in.
    ipAddress = InetAddress.getByName(serverSettings.getString("serverIp"));
} catch (UnknownHostException e) {
    Log.e("ERROR:", "IOException: Failed to create IP, trying default");
}
if(ipAddress==null){
    try {
        // DEFAULT_IP is the hard-coded default fall-back address
        ipAddress = InetAddress.getByName(DEFAULT_IP);

    } catch (UnknownHostException e1) {
        Log.e("ERROR:", "IOException: Total fail, exiting");
        e1.printStackTrace();
        finish();
    }
}

Answer 6

在進行更大規模的測試時，我喜歡另一種變化（在第一次勝利的基礎上）：

ipAddress = null;
// serverSettings is the Bundle name that was passed in.
String[] addresses = { DEFAULT_IP,
                       serverSettings.getString("serverIp") };

int i = 0;
do {
    try {
        ipAddress = InetAddress.getByName(addresses[i]);
    } catch (UnknownHostException e) {
        Log.e("ERROR:", "IOException: Failed to create IP, trying next");
    }
} while (ipAddress == null && i < addresses.length);

if (ipAddress == null) {
    Log.e("ERROR:", "IOException: Total fail, exiting");
    e1.printStackTrace();
    finish();
}

這在我的正常用例中可能更合適（循環使用SimpleDateFormats來匹配第三方日期字符串）