app在执行过程中。为了后期的维护升级，记录日志是一个很好的方法。

为了读取到app执行时的日志，一般的作法是单独开一个线程，在app执行的启动线程。然后app退出时停掉线程。

然而我们更好的方法是开启一个service，然后在里面做日志记录。代码例如以下：

package com.hai.logcat;import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.List;import android.app.ActivityManager;
import android.app.ActivityManager.RunningAppProcessInfo;
import android.app.Service;
import android.content.Intent;
import android.os.Environment;
import android.os.IBinder;
import android.os.Looper;
import android.util.Log;
import android.widget.Toast;public class MyLogcat extends Service {Thread thread;boolean readlog = true;@Overridepublic IBinder onBind(Intent intent) {return null;}@Overridepublic void onCreate() {super.onCreate();Log.d("hhp", "onCreate");thread = new Thread(new Runnable() {@Overridepublic void run() {log2();//个人认为这种方法更有用}});}@Overridepublic void onStart(Intent intent, int startId) {thread.start();Log.d("hhp", "onStart");super.onStart(intent, startId);}/*** 方法1*/private void log2() {Log.d("hhp", "log2 start");String[] cmds = { "logcat", "-c" };String shellCmd = "logcat -v time -s *:W "; // adb logcat -v time *:WProcess process = null;Runtime runtime = Runtime.getRuntime();BufferedReader reader = null;try {runtime.exec(cmds).waitFor();process = runtime.exec(shellCmd);reader = new BufferedReader(new InputStreamReader(process.getInputStream()));String line = null;while ((line = reader.readLine()) != null) {if (line.contains(String.valueOf(android.os.Process.myPid()))) {// line = new String(line.getBytes("iso-8859-1"), "utf-8");writeTofile(line);}}} catch (Exception e) {e.printStackTrace();}Log.d("hhp", "log2 finished");}/*** 方法2*/private void log() {Log.d("hhp", "log start");String[] cmds = { "logcat", "-c" };String shellCmd = "logcat -v time -s *:W ";// //adb logcat -v time *:WProcess process = null;InputStream is = null;DataInputStream dis = null;String line = "";Runtime runtime = Runtime.getRuntime();try {runtime.exec(cmds);process = runtime.exec(shellCmd);is = process.getInputStream();dis = new DataInputStream(is);// String filter = GetPid();String filter = android.os.Process.myPid() + "";while ((line = dis.readLine()) != null) { //这里假设输入流没断。会一直循环下去。line = new String(line.getBytes("iso-8859-1"), "utf-8");if (line.contains(filter)) {int pos = line.indexOf(":");Log.d("hhp2", line + "");writeTofile(line);}}} catch (Exception e) {}Log.d("hhp", "log finished");}private void writeTofile(String line) {String content = line + "\r\n";File file = new File(Environment.getExternalStorageDirectory().getAbsolutePath()+ "/logcat/myLog.txt");if (!file.exists()) {try {file.createNewFile();} catch (Exception e) {e.printStackTrace();}}FileOutputStream fos;try {fos = new FileOutputStream(file, true);fos.write(content.getBytes());fos.flush();fos.close();} catch (Exception e) {e.printStackTrace();}}@Overridepublic void onDestroy() {super.onDestroy();stopSelf();}
}

代码比較简单，所以没怎么注视了。说下大概思路：在service开启的时候。就开启线程不停地从logcat中读取输入流，

把读到的信息存入文件里，service停止的时候线程stop，就这么简单。

当然要读入系统日志还须要加入权限：

<uses-permission android:name="android.permission.READ_LOGS" />

以下是我记录的測试日志,信息记录的有点多。实际中能够运用正则过滤掉一些信息。

上面的代码基本能够记录本app执行中的日志，但假设中途有未捕获的异常导致app奔溃，那么这个未捕获的异常导致的奔溃上面代码就记录不到了。

由于这个异常导致app奔溃，虚拟机挂掉，那当然记录日志的线程也停了。那怎么捕获这类我们未捕获的异常（执行时异常）呢，幸好android这样

一个接口UncaughtExceptionHandler，当app奔溃前。它会先通知这个接口。这样我们就能够在app奔溃前做点自己想做的事了。

关于怎么捕获奔溃异常。我认为这位哥们的一片博客写的不错http://blog.csdn.net/liuhe688/article/details/6584143#。 我借鉴着改了下：

package com.hai.logcat;import java.io.File;
import java.io.FileOutputStream;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.io.Writer;
import java.lang.Thread.UncaughtExceptionHandler;
import java.lang.reflect.Field;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.Build;
import android.os.Environment;
import android.os.Looper;
import android.util.Log;
import android.widget.Toast;public class CrashHandler implements UncaughtExceptionHandler {public static final String TAG = "CrashHandler";// 系统默认的UncaughtException处理类private Thread.UncaughtExceptionHandler mDefaultHandler;// CrashHandler实例private static CrashHandler INSTANCE = new CrashHandler();// 程序的Context对象private Context mContext;// 用来存储设备信息和异常信息private Map<String, String> infos = new HashMap<String, String>();// 用于格式化日期,作为日志文件名称的一部分private DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss  ");/** 保证仅仅有一个CrashHandler实例 */private CrashHandler() {}/** 获取CrashHandler实例 ,单例模式 */public static CrashHandler getInstance() {return INSTANCE;}/*** 初始化* * @param context*/public void init(Context context) {mContext = context;// 获取系统默认的UncaughtException处理器mDefaultHandler = Thread.getDefaultUncaughtExceptionHandler();// 设置该CrashHandler为程序的默认处理器Thread.setDefaultUncaughtExceptionHandler(this);}/*** 当UncaughtException发生时会转入该函数来处理*/@Overridepublic void uncaughtException(Thread thread, Throwable ex) {if (!handleException(ex) && mDefaultHandler != null) {// 假设用户没有处理则让系统默认的异常处理器来处理mDefaultHandler.uncaughtException(thread, ex);} else {try {Thread.sleep(3000);} catch (InterruptedException e) {Log.e(TAG, "error : ", e);}// 退出程序android.os.Process.killProcess(android.os.Process.myPid());System.exit(1);}}/*** 自己定义错误处理,收集错误信息 发送错误报告等操作均在此完毕.* * @param ex* @return true:假设处理了该异常信息;否则返回false.*/private boolean handleException(final Throwable ex) {if (ex == null) {return false;}// 使用Toast来显示异常信息new Thread() {@Overridepublic void run() {Looper.prepare();ex.printStackTrace();Toast.makeText(mContext, "非常抱歉,程序出现异常,即将退出.", Toast.LENGTH_LONG).show();Looper.loop();}}.start();// 收集设备參数信息collectDeviceInfo(mContext);// 保存日志文件saveCrashInfo2File(ex);return true;}/*** 收集设备參数信息* * @param ctx*/public void collectDeviceInfo(Context ctx) {try {PackageManager pm = ctx.getPackageManager();PackageInfo pi = pm.getPackageInfo(ctx.getPackageName(), PackageManager.GET_ACTIVITIES);if (pi != null) {String versionName = pi.versionName == null ? "null" : pi.versionName;String versionCode = pi.versionCode + "";infos.put("versionName", versionName);infos.put("versionCode", versionCode);}} catch (NameNotFoundException e) {Log.e(TAG, "an error occured when collect package info", e);}Field[] fields = Build.class.getDeclaredFields();for (Field field : fields) {try {field.setAccessible(true);infos.put(field.getName(), field.get(null).toString());Log.d(TAG, field.getName() + " : " + field.get(null));} catch (Exception e) {Log.e(TAG, "an error occured when collect crash info", e);}}}/*** 保存错误信息到文件里* * @param ex* @return 返回文件名称称,便于将文件传送到server*/private String saveCrashInfo2File(Throwable ex) {StringBuffer sb = new StringBuffer();for (Map.Entry<String, String> entry : infos.entrySet()) {String key = entry.getKey();String value = entry.getValue();sb.append(key + "=" + value + "\n");}Writer writer = new StringWriter();PrintWriter printWriter = new PrintWriter(writer);ex.printStackTrace(printWriter);Throwable cause = ex.getCause();while (cause != null) {cause.printStackTrace(printWriter);cause = cause.getCause();}printWriter.close();String result = writer.toString();String time = formatter.format(new Date());sb.append(time + result);try {long timestamp = System.currentTimeMillis();String fileName = "crash.log";if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {String path =Environment.getExternalStorageDirectory().getAbsolutePath()+ "/logcat/";File dir = new File(path);if (!dir.exists()) {dir.mkdirs();}FileOutputStream fos = new FileOutputStream(path + fileName, true);fos.write((sb.toString()).getBytes());fos.close();}return fileName;} catch (Exception e) {Log.e(TAG, "an error occured while writing file...", e);}return null;}
}

上面我们实现了这个接口。然后在奔溃前做了一些友优点理。如存储奔溃日志，主动杀死进程，不让弹出系统的强制关闭对话框。

然后我们在Application中这样引用就可以

package com.hai;import android.app.Application;import com.hai.logcat.CrashHandler;public class MyApplication extends Application {CrashHandler handler = null;@Overridepublic void onCreate() {super.onCreate();handler = CrashHandler.getInstance();handler.init(getApplicationContext());}
}