背景

经常会为log定位而烦恼。比如：同一个类，一样的log输出，无法定位到Log输出的行。

方案

1.java StackTraceElement

通过java StackTraceElement获取类名，以及log输出行

2. 具体实现

  @NonNull
  private static String getSourcePoint()
  {
    final StackTraceElement[] stackTrace = new Throwable().getStackTrace();
    assert stackTrace.length > CALL_STACK_INDEX : "Synthetic stacktrace doesn't have enough elements";

    final StackTraceElement st = stackTrace[CALL_STACK_INDEX];
    StringBuilder sb = new StringBuilder(80);
    final String fileName = st.getFileName();
    if (fileName != null)
    {
      sb.append(fileName);
      final int lineNumber = st.getLineNumber();
      if (lineNumber >= 0)
        sb.append(':').append(lineNumber);
      sb.append(' ');
    }
    sb.append(st.getMethodName()).append("()");
    return sb.toString();
  }

3. logger.java实现

package com.app.test.util.log;

import android.util.Log;

import androidx.annotation.Keep;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import com.app.test.BuildConfig;
import net.jcip.annotations.ThreadSafe;


@ThreadSafe
public final class Logger
{
  private static final String TAG = Logger.class.getSimpleName();
  private static final String CORE_TAG = "APP";
  private static final String FILENAME = "app.log";

  public static void v(String tag)
  {
    log(Log.VERBOSE, tag, "", null);
  }

  public static void v(String tag, String msg)
  {
    log(Log.VERBOSE, tag, msg, null);
  }

  public static void v(String tag, String msg, Throwable tr)
  {
    log(Log.VERBOSE, tag, msg, tr);
  }

  public static void d(String tag)
  {
    log(Log.DEBUG, tag, "", null);
  }

  public static void d(String tag, String msg)
  {
    log(Log.DEBUG, tag, msg, null);
  }

  public static void d(String tag, String msg, Throwable tr)
  {
    log(Log.DEBUG, tag, msg, tr);
  }

  public static void i(String tag)
  {
    log(Log.INFO, tag, "", null);
  }

  public static void i(String tag, String msg)
  {
    log(Log.INFO, tag, msg, null);
  }

  public static void i(String tag, String msg, Throwable tr)
  {
    log(Log.INFO, tag, msg, tr);
  }

  public static void w(String tag, String msg)
  {
    log(Log.WARN, tag, msg, null);
  }

  public static void w(String tag, String msg, Throwable tr)
  {
    log(Log.WARN, tag, msg, tr);
  }

  public static void e(String tag, String msg)
  {
    log(Log.ERROR, tag, msg, null);
  }

  public static void e(String tag, String msg, Throwable tr)
  {
    log(Log.ERROR, tag, msg, tr);
  }

  // Index of stacktrace depth where the original log method call resides.
  private static final int CALL_STACK_INDEX = 3;

  @NonNull
  private static String getSourcePoint()
  {
    final StackTraceElement[] stackTrace = new Throwable().getStackTrace();
    assert stackTrace.length > CALL_STACK_INDEX : "Synthetic stacktrace doesn't have enough elements";

    final StackTraceElement st = stackTrace[CALL_STACK_INDEX];
    StringBuilder sb = new StringBuilder(80);
    final String fileName = st.getFileName();
    if (fileName != null)
    {
      sb.append(fileName);
      final int lineNumber = st.getLineNumber();
      if (lineNumber >= 0)
        sb.append(':').append(lineNumber);
      sb.append(' ');
    }
    sb.append(st.getMethodName()).append("()");
    return sb.toString();
  }

  // Also called from JNI to proxy native code logging (with tag == null).
  @Keep
  private static void log(int level, @Nullable String tag, @NonNull String msg, @Nullable Throwable tr)
  {

    if (BuildConfig.DEBUG || level >= Log.INFO)
    {
      final StringBuilder sb = new StringBuilder(180);
      // Add source point info for file logging, debug builds and ERRORs if its not from core.
      if (tag != null && (BuildConfig.DEBUG || level == Log.ERROR))
        sb.append(getSourcePoint()).append(": ");
      sb.append(msg);
      if (tr != null)
        sb.append('\n').append(Log.getStackTraceString(tr));
      if (tag == null)
        tag = CORE_TAG;

      if (logsFolder == null || BuildConfig.DEBUG)
        Log.println(level, tag, sb.toString());

    }
  }

  private static char getLevelChar(int level)
  {
    switch (level)
    {
      case Log.VERBOSE:
        return 'V';
      case Log.DEBUG:
        return 'D';
      case Log.INFO:
        return 'I';
      case Log.WARN:
        return 'W';
      case Log.ERROR:
        return 'E';
    }
    assert false : "Unknown log level " + level;
    return '_';
  }
}

4. 结果：

如上图，可以看到log输出java的类名，以及行。 

总结

略