通常我们在开发应用的时候需要将日志打印到终端，而当应用发布的时候就需要将日志记录到本地文件，因此在具体实现的时候使用了简单工厂模式。本地日志的实现已经有很多现成的优秀开源库，这里就不再重复造轮子了，本文使用的是Apache的开源库log4j，版本号1.2.17。下面来介绍具体实现。

先来预览一下文件目录结构：

ILog.java文件

package xxx.log;

public interface ILog {
    int LEVEL_TRACE = 0;
    int LEVEL_DEBUG = 1;
    int LEVEL_INFO = 2;
    int LEVEL_WARN = 3;
    int LEVEL_ERROR = 4;
    int LEVEL_FATAL = 5;

    void t(Object msg);
    void d(Object msg);
    void i(Object msg);
    void w(Object msg);
    void e(Object msg);
}

LogPrintImpl.java

package xxx.log;

import android.util.Log;

public class LogPrintImpl implements ILog {
    private final String mTag;
    private final int mLevel;

    public LogPrintImpl(int level, String tag) {
        mTag = tag;
        mLevel = level;
    }

    @Override
    public void t(Object msg) {
        if (mLevel > LEVEL_TRACE) {
            return;
        }
        if (!(msg instanceof String)) {
            msg = msg.toString();
        }
        Log.d(mTag, (String)msg);
    }

    @Override
    public void d(Object msg) {
        if (mLevel > LEVEL_DEBUG) {
            return;
        }
        if (!(msg instanceof String)) {
            msg = msg.toString();
        }
        Log.d(mTag, (String)msg);
    }

    @Override
    public void i(Object msg) {
        if (mLevel > LEVEL_INFO) {
            return;
        }
        if (!(msg instanceof String)) {
            msg = msg.toString();
        }
        Log.i(mTag, (String)msg);
    }

    @Override
    public void w(Object msg) {
        if (mLevel > LEVEL_WARN) {
            return;
        }
        if (!(msg instanceof String)) {
            msg = msg.toString();
        }
        Log.w(mTag, (String)msg);
    }

    @Override
    public void e(Object msg) {
        if (mLevel > LEVEL_ERROR) {
            return;
        }
        if (!(msg instanceof String)) {
            msg = msg.toString();
        }
        Log.e(mTag, (String)msg);
    }
}

LogFileImpl.java

package xxx.log;

import org.apache.log4j.Level;
import org.apache.log4j.PatternLayout;
import org.apache.log4j.RollingFileAppender;

import java.io.IOException;

public class LogFileImpl implements ILog {
    //constant
    private static final int MAX_FILE_SIZE = 10 * 1024 * 1024;//10M bytes

    //non-constant
    private final String mTag;
    private org.apache.log4j.Logger mLogger;

    public LogFileImpl(int level, String tag, String path) {
        mTag = tag;
        init(path, level);
    }

    public void init(String path, int level) {
        PatternLayout patternLayout = new PatternLayout();
        patternLayout.setConversionPattern("%d{yyyy-MM-dd HH:mm:ss} -%-5.5p- %m %n");

        RollingFileAppender rollingFileAppender = null;
        try {
            rollingFileAppender = new RollingFileAppender(patternLayout, path, true);
            rollingFileAppender.setMaximumFileSize(MAX_FILE_SIZE);
            rollingFileAppender.setMaxBackupIndex(2);
        } catch (IOException ex) {
        }

        mLogger = org.apache.log4j.Logger.getLogger(mTag);
        mLogger.addAppender(rollingFileAppender);

        Level l;
        switch(level) {
            case LEVEL_TRACE:
                l = Level.TRACE;
                break;
            case LEVEL_DEBUG:
                l = Level.DEBUG;
                break;
            case LEVEL_INFO:
                l = Level.INFO;
                break;
            case LEVEL_ERROR:
                l = Level.ERROR;
                break;
            case LEVEL_FATAL:
                l = Level.FATAL;
                break;
            default:
                l = Level.ERROR;
                break;
        }

        mLogger.setLevel(l);
    }

    @Override
    public void t(Object msg) {
        if (mLogger != null) {
            mLogger.trace(msg);
        }
    }

    @Override
    public void d(Object msg) {
        if (mLogger != null) {
            mLogger.debug(msg);
        }
    }

    @Override
    public void i(Object msg) {
        if (mLogger != null) {
            mLogger.info(msg);
        }
    }

    @Override
    public void w(Object msg) {
        if (mLogger != null) {
            mLogger.warn(msg);
        }
    }

    @Override
    public void e(Object msg) {
        if (mLogger != null) {
            mLogger.error(msg);
        }
    }
}

LogFactory.java

package xxx.log;

public class LogFactory {
    public ILog createLogger(int type, int level, String tag, String path) {
        ILog instance = null;
        switch(type) {
            case 0:
                instance = new LogPrintImpl(level, tag);
                break;
            case 1:
                instance = new LogFileImpl(level, tag, path);
                break;
            default:
                break;
        }
        return instance;
    }
}

LogUtil.java

package xxx.log;

public class LogUtils {
    private static ILog mLogger;

    public static void init(int type, int level, String tag, String path) {
        if (mLogger == null) {
            synchronized (LogUtils.class) {
                if (mLogger == null) {
                    LogFactory logFactory = new LogFactory();
                    mLogger = logFactory.createLogger(type, level, tag, path);
                }
            }
        }
    }

    public static void t(Object msg) {
        if (mLogger != null) {
            mLogger.t(msg);
        }
    }

    public static void d(Object msg) {
        if (mLogger != null) {
            mLogger.d(msg);
        }
    }

    public static void i(Object msg) {
        if (mLogger != null) {
            mLogger.i(msg);
        }
    }

    public static void w(Object msg) {
        if (mLogger != null) {
            mLogger.w(msg);
        }
    }

    public static void e(Object msg) {
        if (mLogger != null) {
            mLogger.e(msg);
        }
    }
}

使用日志类

LogUtils.init(0, ILog.LEVEL_INFO, "TAG", "");
//LogUtils.init(1, ILog.LEVEL_INFO, "TAG", "/sdcard/log");
LogUtils.i("Hello world!");