我想使用属性文件来读取我的 Android 应用程序中的一些配置数据。当我将属性文件放置在处理程序的类文件夹中时,一切正常,但我想将属性文件放置在项目根目录中。我已经尝试使用相对路径(../../../
等),但它不起作用。
有没有一种“简单”的方法可以做到这一点(/config.properties
也不起作用)?
这是我的代码:
private Properties prop;
public PropertiesHandler() {
this.prop = new Properties();
InputStream input = null;
try {
input = getClass().getResourceAsStream("config.properties");
//input = new FileInputStream("config.properties");
prop.load(input);
} catch (IOException ex) {
ex.printStackTrace();
} finally {
if (input != null) {
try {
input.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
任何帮助将不胜感激。
编辑:
不幸的是,我在应用建议的解决方案时遇到了此异常:
10-08 15:10:05.903: E/AndroidRuntime(967): FATAL EXCEPTION: main
10-08 15:10:05.903: E/AndroidRuntime(967): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.dev.app1234/com.dev.app1234.Register}: java.lang.NullPointerException
10-08 15:10:05.903: E/AndroidRuntime(967): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
10-08 15:10:05.903: E/AndroidRuntime(967): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
10-08 15:10:05.903: E/AndroidRuntime(967): at android.app.ActivityThread.access$600(ActivityThread.java:130)
10-08 15:10:05.903: E/AndroidRuntime(967): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-08 15:10:05.903: E/AndroidRuntime(967): at android.os.Handler.dispatchMessage(Handler.java:99)
10-08 15:10:05.903: E/AndroidRuntime(967): at android.os.Looper.loop(Looper.java:137)
10-08 15:10:05.903: E/AndroidRuntime(967): at android.app.ActivityThread.main(ActivityThread.java:4745)
10-08 15:10:05.903: E/AndroidRuntime(967): at java.lang.reflect.Method.invokeNative(Native Method)
10-08 15:10:05.903: E/AndroidRuntime(967): at java.lang.reflect.Method.invoke(Method.java:511)
10-08 15:10:05.903: E/AndroidRuntime(967): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-08 15:10:05.903: E/AndroidRuntime(967): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-08 15:10:05.903: E/AndroidRuntime(967): at dalvik.system.NativeStart.main(Native Method)
10-08 15:10:05.903: E/AndroidRuntime(967): Caused by: java.lang.NullPointerException
10-08 15:10:05.903: E/AndroidRuntime(967): at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:101)
10-08 15:10:05.903: E/AndroidRuntime(967): at com.dev.app1234.Register.<init>(Register.java:68)
10-08 15:10:05.903: E/AndroidRuntime(967): at java.lang.Class.newInstanceImpl(Native Method)
10-08 15:10:05.903: E/AndroidRuntime(967): at java.lang.Class.newInstance(Class.java:1319)
10-08 15:10:05.903: E/AndroidRuntime(967): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
10-08 15:10:05.903: E/AndroidRuntime(967): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
10-08 15:10:05.903: E/AndroidRuntime(967): ... 11 more
这是我的代码:
public PropertiesHandler(Context context) {
this.prop = new Properties();
InputStream input = null;
try {
input = context.getAssets().open("config.properties");
我这样调用它:
private final String URL = new PropertiesHandler(this.getApplicationContext()).getUrl()
+ "url.php";
编辑2:
代码:
private final String URL = new PropertiesHandler(Register.this).getUrl()
+ "url.php";
堆栈跟踪:
10-08 20:45:14.421: E/AndroidRuntime(1024): FATAL EXCEPTION: main
10-08 20:45:14.421: E/AndroidRuntime(1024): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.dev.app1234/com.dev.app1234.Register}: java.lang.NullPointerException
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.app.ActivityThread.access$600(ActivityThread.java:130)
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.os.Handler.dispatchMessage(Handler.java:99)
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.os.Looper.loop(Looper.java:137)
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.app.ActivityThread.main(ActivityThread.java:4745)
10-08 20:45:14.421: E/AndroidRuntime(1024): at java.lang.reflect.Method.invokeNative(Native Method)
10-08 20:45:14.421: E/AndroidRuntime(1024): at java.lang.reflect.Method.invoke(Method.java:511)
10-08 20:45:14.421: E/AndroidRuntime(1024): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-08 20:45:14.421: E/AndroidRuntime(1024): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-08 20:45:14.421: E/AndroidRuntime(1024): at dalvik.system.NativeStart.main(Native Method)
10-08 20:45:14.421: E/AndroidRuntime(1024): Caused by: java.lang.NullPointerException
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.content.ContextWrapper.getAssets(ContextWrapper.java:75)
10-08 20:45:14.421: E/AndroidRuntime(1024): at com.dev.app1234.model.PropertiesHandler.<init>(PropertiesHandler.java:25)
10-08 20:45:14.421: E/AndroidRuntime(1024): at com.dev.app1234.Register.<init>(Register.java:68)
10-08 20:45:14.421: E/AndroidRuntime(1024): at java.lang.Class.newInstanceImpl(Native Method)
10-08 20:45:14.421: E/AndroidRuntime(1024): at java.lang.Class.newInstance(Class.java:1319)
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
10-08 20:45:14.421: E/AndroidRuntime(1024): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
10-08 20:45:14.421: E/AndroidRuntime(1024): ... 11 more
最佳答案
此调用:
private final String URL = new PropertiesHandler(Register.this).getUrl() + "url.php";
需要放置在 Activity 的 onCreate()
内方法。就像这样:
class Register extends Activity {
private String URL;
// ...
protected void onCreate(Bundle savedInstanceState) {
// ...
URL = new PropertiesHandler(Register.this).getUrl() + "url.php";
// ...
}
}
通过在创建 Activity 之前创建自定义类,您可以有效地传递 null
在此代码中:new PropertiesHandler(Register.this)
,因此堆栈跟踪中会出现空指针错误。
像这样的错误经常发生,因为 Android 中许多有用的系统调用都需要 Context
。发生这种情况的一个很好的线索是在堆栈跟踪中看到对 <init>
的引用。虚方法,指类中未包含在其他方法中的所有变量初始值设定项。就像给出的堆栈跟踪中的这一行一样:
10-08 20:45:14.421: E/AndroidRuntime(1024): at com.dev.app1234.Register.<init>(Register.java:68)
关于java - 在 Android 应用程序中使用属性文件时出现 NullPointerException,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/26242009/