在java核心库中，由于无法导入android的包，要想使用Log，最粗暴的方式就是用反射调用，还有一种方式就是移植Android的Log到java核心库中。

具体实现如下：

创建JLog.java

aosp/libcore/ojluni/src/main/java/java/langpackage java.lang;import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.json.JSONObject;public class JLog {public static final String mTag = "Yooha-log";public static final int INFO = 4;public static final int ERROR = 6;public static native int println_native(int bufID, int priority, String tag, String msg);public static native int getpid();public static void print_info(String tag, String info) {try{JSONObject jsinfo = new JSONObject();jsinfo.put("Type", tag);jsinfo.put("PID", getProcessID());jsinfo.put("Info", info);i(mTag, jsinfo.toString());} catch (Exception e){showException(e);}}public static void print_stack(String type, String clz, String method, String ret, String...param) {try{JSONObject jsinfo = new JSONObject();jsinfo.put("Type", type);jsinfo.put("PID", getProcessID());jsinfo.put("Class", clz);jsinfo.put("Method", method);if (param != null){jsinfo.put("Param", param.toString());}else{jsinfo.put("Param", "NULL");}if (ret == null){jsinfo.put("Return", "NULL");}else{jsinfo.put("Return", ret);}jsinfo.put("stackTrace", getStackTrace());i(mTag, jsinfo.toString());} catch (Exception e){showException(e);}}public static String getStackTrace() {StringBuffer sb = new StringBuffer();try{Throwable ex = new Throwable();StackTraceElement[] stackElements = ex.getStackTrace();for (int i = 0; i < stackElements.length; i++) {StackTraceElement element = stackElements[i];sb.append("at " +element.getClassName() +"." +element.getMethodName() +"(" +element.getFileName() +":" +element.getLineNumber() +")\n");}} catch(Exception e){}return sb.toString();}public static void showException(Exception e){e(mTag, "Type:Exception, ExceptionLine:" + getExceptionLine() + ", Exception:" + e.toString());}public static String getExceptionLine(){StackTraceElement element = new Throwable().getStackTrace()[1];return element.getFileName() + "-->" + element.getLineNumber() + " : " + element.getClassName();}public static int getProcessID(){try{return getpid();} catch (Exception e){}return -1;}public static int i(String tag, String msg){return println_native(0, INFO, tag, msg);}public static int e(String tag, String msg){return println_native(0, ERROR, tag, msg);}
}

• 将JLog.java文件添加到编译文件链

- 路径：/home/yooha/aosp/libcore/penjdk_java_files.bpfilegroup {name: "openjdk_javadoc_files",srcs: [...省略"ojluni/src/main/java/java/lang/System.java",///ADD START"ojluni/src/main/java/java/lang/JLog.java",///ADD END"ojluni/src/main/java/java/lang/ThreadDeath.java",...省略],
}

• 在libcore native层添加JLog.c

/aosp/libcore/ojluni/src/main/native#include <log/log.h>
#include <utils/Log.h>
#include <jni.h>
#include <nativehelper/JNIHelp.h>
//#include <process.h>
#include <unistd.h>static jint java_lang_JLog_println_native(JNIEnv* env, jclass clazz,jint bufID, jint priority, jstring tagObj, jstring msgObj)
{const char* tag = NULL;const char* msg = NULL;if (msgObj == NULL) {//JNU_ThrowNullPointerException(env, "println needs a message");return -1;}if (bufID < 0 || bufID >= LOG_ID_MAX) {//JNU_ThrowNullPointerException(env, "bad bufID");return -1;}if (tagObj != NULL)tag = (*env)->GetStringUTFChars(env,tagObj, NULL);msg = (*env)->GetStringUTFChars(env,msgObj, NULL);int res = __android_log_buf_write(bufID, (android_LogPriority)priority, tag, msg);if (tag != NULL)(*env)->ReleaseStringUTFChars(env,tagObj, tag);(*env)->ReleaseStringUTFChars(env,msgObj, msg);return res;
}static jint java_lang_JLog_getpid(JNIEnv* env, jclass clazz){return getpid();
}static const JNINativeMethod gMethods[] = {/* name, signature, funcPtr */{ "println_native",  "(IILjava/lang/String;Ljava/lang/String;)I", (void*) java_lang_JLog_println_native },{ "getpid",  "()I", (void*) java_lang_JLog_getpid }
};void register_java_lang_JLog(JNIEnv* env) {jniRegisterNativeMethods(env, "java/lang/JLog", gMethods, NELEM(gMethods));
}

• OnLoad.cpp中声明和调用 register_java_lang_JLog

- 路径：libcore/ojluni/src/main/native/OnLoad.cpp...省略
///ADD START
extern "C" void register_java_lang_JLog(JNIEnv* env);
///ADD END
...省略
extern "C" JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void*) {...省略///ADD STARTregister_java_lang_JLog(env);///ADD END...省略
}
...省略

• Android.bp中添加XLog.c文件到编译文件中

- 路径：/home/yooha/aosp/libcore/ojluni/src/main/native/Android.bpfilegroup {name: "libopenjdk_native_srcs",srcs: [...省略///ADD START"JLog.c",///ADD END...省略],
}

最后编译刷机，就可以正常使用了