解析xml android给出一个空指针异常

Question

我正在解析以下XML:

<?xml version="1.0"?>
<Root>
    <ResponseCode>1</ResponseCode>
    <ResponseMessage>Login Successfull</ResponseMessage>
    <ResultSet>
        <User>
            <id>3</id>
            <username>hassan</username>
            <email>hassan</email>
            <password>abcd</password>
            <profileimagepath>c:/hahaha/hahaha</profileimagepath>
            <createdOn>2013-03-23 12:45:51</createdOn>
            <status>1</status>
        </User>
    </ResultSet>
</Root>

我用来解析XML的代码是:

InputSource is = new InputSource();
is.setCharacterStream(new StringReader(xmlResult));
XPathFactory factory = XPathFactory.newInstance();
XPath xPath = factory.newXPath();
try {
    NodeList list = (NodeList) xPath.evaluate("/Root", is,XPathConstants.NODESET);
    for(int i=0; i<list.getLength(); i++){
        Node node = list.item(i);
        Element element = (Element) node;
        Log.d("VALUE OF NODE", element.getNodeValue());
    }
} catch (XPathExpressionException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

我无法判断为什么会出现这个异常。解析它的正确方法是什么?我在Android 4.0上执行此操作。这是logcat

03-24 01:50:54.412: I/Post service Response(1097): <?xml version="1.0"?><Root><ResponseCode>1</ResponseCode><ResponseMessage>Login Successfull</ResponseMessage><ResultSet><User><id>3</id><username>hassan</username><email>hassan</email><password>abcd</password><profileimagepath>c:/hahaha/hahaha</profileimagepath><createdOn>2013-03-23 12:45:51</createdOn><status>1</status></User></ResultSet></Root>
03-24 01:50:54.804: D/dalvikvm(1097): GC_CONCURRENT freed 1940K, 21% free 7888K/9927K, paused 11ms+15ms
03-24 01:50:55.284: W/dalvikvm(1097): threadid=11: thread exiting with uncaught exception (group=0x409961f8)
03-24 01:50:55.293: E/AndroidRuntime(1097): FATAL EXCEPTION: Thread-102
03-24 01:50:55.293: E/AndroidRuntime(1097): java.lang.NullPointerException: println needs a message
03-24 01:50:55.293: E/AndroidRuntime(1097):     at android.util.Log.println_native(Native Method)
03-24 01:50:55.293: E/AndroidRuntime(1097):     at android.util.Log.d(Log.java:138)
03-24 01:50:55.293: E/AndroidRuntime(1097):     at com.teamgreen.greenit.LoginActivity$1$1.run(LoginActivity.java:87)
03-24 01:51:28.253: I/Process(1097): Sending signal. PID: 1097 SIG: 9

Answer 1

你从Log.d()内部得到一个异常，因为element.getNodeValue()返回null。

不能提供null作为Log.d()的第二个参数。考虑将各自的行更改为:

Log.d("xml", "VALUE OF NODE: " + element.getNodeValue());

不要专注于特定的问题，而应该尝试理解解释堆栈跟踪。堆栈跟踪指向确切的问题:

E/AndroidRuntime(1097): at android.util.Log.d(Log.java:138)
E/AndroidRuntime(1097): at com.teamgreen.green . loginactivity $1$1.run(LoginActivity.java:87)