标题: 上哪儿查看System.err.println()的输出

https://scz.617.cn/android/201701161610.txt

Q:

APK中有如下代码:

--------------------------------------------------------------------------
try
{
    System.loadLibrary( "sczutiljni" );
}
catch ( UnsatisfiedLinkError e )
{
    System.err.println( "Cannot load sczutiljni [" + e.toString() + "]" );
}
--------------------------------------------------------------------------

上哪儿查看System.err.println()的输出？

A: scz

对于Android开发，不建议使用System.err.println()，应该直接使用logcat机制

https://developer.android.com/studio/command-line/logcat.html
https://developer.android.com/reference/android/util/Log.html

--------------------------------------------------------------------------
import android.util.Log;

Log.<log level>( "<your tag>", "<your msg>" );

v
d
i
w
e
--------------------------------------------------------------------------

从Android SDK Build-tools 21.0.3开始，TAG被限制在23个字符以内。

System.err.println()相当于:

Log.w( "System.err", "..." )

System.out.println相当于:

Log.i( "System.out", "..." )

这个与log.redirect-stdio属性无关。

$ adb shell "ps | grep com.anything.crackmegui_jni"
u0_a47     1789 27933 326008 28104 ffffffff b7700827 S com.anything.crackmegui_jni

$ adb shell "logcat -d -v brief -s System.err:W | grep -E \"W/System.err\( 1789\):\""
$ adb logcat -d -v brief -s "System.err:W" | grep -E "W/System.err\( 1789\):"
W/System.err( 1789): Cannot load sczutiljni [java.lang.UnsatisfiedLinkError: Couldn't load sczutiljni from loader dalvik.system.PathClassLoader[dexPath=/data/app/com.anything.crackmegui_jni-1.apk,libraryPath=/data/app-lib/com.anything.crackmegui_jni-1]: findLibrary returned null]

与之类似:

$ adb shell "logcat -d -v brief -s System.out:I | grep -E \"I/System.out\( 1789\):\""
$ adb logcat -d -v brief -s "System.out:I" | grep -E "I/System.out\( 1789\):"
I/System.out( 1789): ...

注意PID固定占5个字节，不足5个字节时左侧用空格补齐。

在Android Studio中使用logcat更方便。在左下角选中Android Monitor标签页，
"Edit Filter Configuration"可以设置很细粒度的过滤规则，包括:

Log Tag
Log Message
Package Name
PID
Log Level

未被捕捉的UnsatisfiedLinkError异常:

$ adb shell "logcat -d -v brief -s AndroidRuntime:E"
E/AndroidRuntime( 3141): FATAL EXCEPTION: main
E/AndroidRuntime( 3141): java.lang.UnsatisfiedLinkError: Native method not found: com.anything.sczutil.HashUtility.gethash_via_jni:(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
E/AndroidRuntime( 3141):        at com.anything.sczutil.HashUtility.gethash_via_jni(Native Method)
E/AndroidRuntime( 3141):        at com.anything.sczutil.HashUtility.VerifyHash(HashUtility.java:65)
E/AndroidRuntime( 3141):        at com.anything.crackmegui_jni.SecretActivity$2.onClick(SecretActivity.java:73)
E/AndroidRuntime( 3141):        at android.view.View.performClick(View.java:4204)
E/AndroidRuntime( 3141):        at android.view.View$PerformClick.run(View.java:17355)
E/AndroidRuntime( 3141):        at android.os.Handler.handleCallback(Handler.java:725)
E/AndroidRuntime( 3141):        at android.os.Handler.dispatchMessage(Handler.java:92)
E/AndroidRuntime( 3141):        at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime( 3141):        at android.app.ActivityThread.main(ActivityThread.java:5041)
E/AndroidRuntime( 3141):        at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 3141):        at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime( 3141):        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
E/AndroidRuntime( 3141):        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
E/AndroidRuntime( 3141):        at dalvik.system.NativeStart.main(Native Method)