在Java中嵌套try/catch語句是否可接受？

Question

我想從傳入的值（使用Bundle）在Android中創建一個IP地址，如果失敗，我使用硬編碼的默認IP地址創建它。如果失敗，我退出應用程序。

我想知道的是，如果它可以像我在這裏做的那樣嵌套try/catch的，或者有更好的方法。

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。它對我來說看起來很笨重，我可能會以不同的方式做，但它是有效的，並且有效。

以下是我會做：

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

這是確定的。你也可以使用一個在第一個catch中被打開的布爾標誌，所以如果你的布爾標誌被打開，你可以通過catch之外的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 3

我認爲這將是值得商榷什麼樣的方式更好，但這裏的另一種選擇，有些人可能認爲是一個有點「表現」和可讀性，雖然它是多行代碼：

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

然後在你的代碼，只是做：

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

Answer 4

我喜歡這個。它有點乾淨，不需要額外的標誌。

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 5

另一種變化是設置默認第一：

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值調用失敗，則異常ip地址之前拋出被修改，所以ip地址已設置爲默認。當然，如果DEFAULT_IP應該總是可以解析的，這只是一個有效的模式。

Answer 6

另一種變型，通過更大的一組測試工作時，我喜歡（以先勝的基礎上）：

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(); 
} 

這可能是我在正常使用情況下，更合適的（通過SimpleDateFormats循環匹配3 -party日期字符串）