将log保存到本地

app在现场测试,发生crash时无法从logcat找到原因,如能将发生错误时的log记录下来,对debug非常有利.
关键接口:Thread.UncaughtExceptionHandler用来捕获运行时未被程序捕获的异常
关键方法
@Override
public void uncaughtException(Thread thread, Throwable ex) {
//错误发生后要执行的操作,如保存错误报告
//这个是最关键的函数，当程序中有未被捕获的异常，系统将会自动调用#uncaughtException方法
//thread为出现未捕获异常的线程，ex为未捕获的异常，有了这个ex，我们就可以得到异常信息。报告
}
通过Thread.setDefaultUncaughtExceptionHandler()方法将异常处理类设置到线程上即可.

下面是收集log的工具类的范例代码:

public class LogCollectionUtil implements UncaughtExceptionHandler {

private Context mContext;

private static final String SDCARD_PATH = Environment
            .getExternalStorageDirectory().toString();

// 系统默认的异常处理(默认情况下系统会终止当前的异常程序)
private UncaughtExceptionHandler mUncaughtExceptionHandler;

private CopyOfLogCollectionUtil2() {
    };

private static CopyOfLogCollectionUtil2 instance = new CopyOfLogCollectionUtil2();

public static CopyOfLogCollectionUtil2 getLogCollectionUtil() {
return instance;
    }

/**
 * 初始化,注册Context对象, 获取系统默认的UncaughtException处理器, 设置该CrashHandler为程序的默认处理器
 * 
 * @param context
 */
public void setCrashHandler(Context context) {
        mContext = context;
        Thread.setDefaultUncaughtExceptionHandler(this);
    }

/**
 * 当uncaughtException发生时会转入该函数处理
 */
@Override
public void uncaughtException(Thread thread, Throwable ex) {
        dumpExceptionToSDCard(mContext, ex);
        showToast(mContext, "我挂了...");
try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
// 如果系统提供了默认异常处理器，交给系统结束我们的程序，否则自己结束自己
if (mUncaughtExceptionHandler != null) {
            mUncaughtExceptionHandler.uncaughtException(thread, ex);
        } else {
            android.os.Process.killProcess(android.os.Process.myPid());
            System.exit(1);
        }
    }

/**
 * save exception info to sd
 * 
 * @param context
 * @param ex
 * @return
 */

private void dumpExceptionToSDCard(Context context, Throwable ex) {

        String fileName = createFile();

try {
            PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter(
                    fileName)));
            dumpPhoneInfo(pw);
            pw.println();
            dumpCrashInfo(ex, pw);
            pw.close();
        } catch (Exception e) {
            Log.e("dd", "dump crash info failed");
        }
    }

/**
 * create file in SDCard
 * 
 * @return
 */
private String createFile() {
        String fileName;
        File dir = null;
if (Environment.getExternalStorageState().equals(
                Environment.MEDIA_MOUNTED)) {
            dir = new File(SDCARD_PATH + File.separator + "crash" + File.separator);
if (!dir.exists()) {
                dir.mkdir();
            }
        }
return fileName = dir.toString() + File.separator
                + parseTime(System.currentTimeMillis()) + ".log";
    }

/**
 * collect device info
 * 
 * @param pw
 * @throws NameNotFoundException
 */
private void dumpPhoneInfo(PrintWriter pw) throws NameNotFoundException {
        PackageManager pm = mContext.getPackageManager();
        PackageInfo packageInfo = pm.getPackageInfo(mContext.getPackageName(),
                PackageManager.GET_ACTIVITIES);
        pw.println("App version: " + packageInfo.versionName + '_'
                + packageInfo.versionCode);
        pw.println("OS version: " + Build.VERSION.RELEASE + '_'
                + Build.VERSION.SDK_INT);
// The manufacturer of the product/hardware.
        pw.println("Vendor: " + Build.MANUFACTURER);
        pw.println("Model: " + Build.MODEL);
        pw.println("Product: " + Build.PRODUCT);
        pw.println("Brand: " + Build.BRAND);
        pw.println("Display: " + Build.DISPLAY);
        pw.println("Device: " + Build.DEVICE);
        pw.println("CPU abi: " + Build.CPU_ABI);
        pw.println("Fingerprint: " + Build.FINGERPRINT);
    }

/**
 * collect log info
 * 
 * @param throwable
 * @param pw
 */
private void dumpCrashInfo(Throwable throwable, PrintWriter pw) {
        throwable.printStackTrace(pw);
    }

/**
 * format time
 * 
 * @param milliseconds
 * @return
 */
private String parseTime(long milliseconds) {
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        format.setTimeZone(TimeZone.getDefault());
        String times = format.format(new Date(milliseconds));
return times;
    }

/**
 * give user tips
 * 
 * @param context
 * @param msg
 */
private void showToast(final Context context, final String msg) {
new Thread(new Runnable() {
@Override
public void run() {
                Looper.prepare();
                Toast.makeText(context, msg, Toast.LENGTH_LONG).show();
                Looper.loop();
            }
        }).start();
    }

}

使用时将以上代码放到你的包里,将如下代码添加到application类的onCreate()方法里即可使用(放在activity的onCreate()方法里也是可以的,这样只能捕获这个activity的crash,定义在application类里可以捕获app所有线程的异常.).
LogCollectionUtil mLogCollection=LogCollectionUtil.getLogCollectionUtil();
mLogCollection.setCrashHandler(this);
发生crash后,在你手机里的crash文件夹下寻找log.