[Android]Android 直接打开log的一种方法

针对Apk log内部控制方式是通过Log.isLoggable来控制的情况

Example: adb shell setprop log.tag.Finsky VERBOSE

一般code是这样写的：
import android.util.Log;

public class FinskyLog
{
public static final boolean DEBUG = Log.isLoggable(TAG, 2);
private static String TAG = “Finsky”;

Log.isLoggable的实现：
Native层处理文件：android_util_Log.cpp (\frameworks\base\core\jni)

Java 定义在Log.java \frameworks\base\core\java\android\util
public static native boolean isLoggable(String tag, int level);
非常有助于无source code apk的debug,比如google apk

struct levels_t {

jint verbose;
jint debug;
jint info;
jint warn;
jint error;
jint assert;

};
static levels_t levels;

static int toLevel(const char* value)
{

switch (value[0]) {
    case 'V': return levels.verbose;
    case 'D': return levels.debug;
    case 'I': return levels.info;
    case 'W': return levels.warn;
    case 'E': return levels.error;
    case 'A': return levels.assert;
    case 'S': return -1; // SUPPRESS
}
return levels.info;

}

static jboolean isLoggable(const char* tag, jint level) {

String8 key;
key.append(LOG_NAMESPACE);
key.append(tag);

char buf[PROPERTY_VALUE_MAX];
if (property_get(key.string(), buf, "") <= 0) {
    buf[0] = '\0';
}

int logLevel = toLevel(buf);
return logLevel >= 0 && level >= logLevel;

}