Android异常 NullPointerException: Attempt to invoke virtual method int java.lang.Integer.intValue()

异常详情

05-23 16:15:41.672  4206  6875 E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.Integer.intValue()' on a null object reference
05-23 16:15:41.672  4206  6875 E AndroidRuntime:    at org.libjingle.LibjingleWrapper$MessageEventHandler.handleMessage(LibjingleWrapper.java:310)
05-23 16:15:41.672  4206  6875 E AndroidRuntime:    at android.os.Handler.dispatchMessage(Handler.java:102)
05-23 16:15:41.672  4206  6875 E AndroidRuntime:    at android.os.Looper.loop(Looper.java:142)
05-23 16:15:41.672  4206  6875 E AndroidRuntime:    at android.os.HandlerThread.run(HandlerThread.java:61)

相关代码

private static Map<String, Integer> downloadingFiles = null;
...
downloadingFiles.put(fileInfo.strFileName, msgId);
...
int msgid = downloadingFiles.get(serverFileName);

问题原因：

@1. 当serverFileName为null时，Map.get(Object key)会产生异常

java.lang.NullPointerException if the specified key is null and this map does not permit null keys (optional)

@2. 当downloadingFiles.get(serverFileName)为null时，会产生NullPointerException

解决方法：

将如下代码
int msgid = downloadingFiles.get(serverFileName);
更改为：
public int getId(String serverFileName) {
if (null ！= serverFileName && downloadingFiles.containsKey(serverFileName)) {
return downloadingFiles.get(serverFileName);
}
return 0;
}

不要直接调用Map.get(Object key)方法，应该先判断Map.containsKey(String key)是否包含该字段，然后再从中取。