# 第四十二周ARTS总结

# Algorithm

Group Anagrams (opens new window)

6ms | 99.49% Run time
45.6MB | 34.50% Memory

public List<List<String>> groupAnagrams(String[] strs) {
    Map<String, List<String>> map = new HashMap<>();

    for (String str : strs) {
        String sortedStr = sort(str);
        List<String> value = map.get(sortedStr);

        if (value == null) {
            value = new ArrayList<>();
            map.put(sortedStr, value);
        }

        value.add(str);
    }

    return new ArrayList<>(map.values());
}

/**
 * 对字符串按照字符进行排序
 *
 * @param str 原始字符串
 * @return 排序完之后的字符串
 */
private String sort(String str) {
    char[] chars = str.toCharArray();
    Arrays.sort(chars);
    return new String(chars);
}

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# Review

How to Promote an App on the App Store and Google Play (opens new window)

# Tip

优雅实现保活 [1] ：

申请白名单

配置权限

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

判断是否在白名单中

@RequiresApi(api = Build.VERSION_CODES.M)
private boolean isIgnoringBatteryOptimizations() {
    boolean isIgnoring = false;
    PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE);
    if (powerManager != null) {
        isIgnoring = powerManager.isIgnoringBatteryOptimizations(getPackageName());
    }
    return isIgnoring;
}

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申请白名单

@RequiresApi(api = Build.VERSION_CODES.M)
public void requestIgnoreBatteryOptimizations() {
    try {
        Intent intent = new Intent(Settings.ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS);
        intent.setData(Uri.parse("package:" + getPackageName()));
        startActivity(intent);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

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加入厂商后台管理白名单（需针对不同厂商进行适配）

如何优雅的打印一个Java对象 [2] (opens new window)
- 对象：实现toString()方法
- 数组：使用Arrays.toString()

防止二次打包最普遍方式 [3] ：签名校验

  private boolean doNormalSignCheck() {
      String trueSignMD5 = "d0add9987c7c84aeb7198c3ff26ca152";
      String nowSignMD5 = "";
      try {
          // 得到签名的MD5
          PackageInfo packageInfo = getPackageManager().getPackageInfo(
                  getPackageName(),
                  PackageManager.GET_SIGNATURES);
          Signature[] signs = packageInfo.signatures;
          String signBase64 = Base64Util.encodeToString(signs[0].toByteArray());
          nowSignMD5 = MD5Utils.MD5(signBase64);
      } catch (PackageManager.NameNotFoundException e) {
          e.printStackTrace();
      }
      return trueSignMD5.equals(nowSignMD5);
  }

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去除签名校验方法 [4] ：

替换原先的Application
在attachBaseContext里初始化hook
动态代理IPackageManager
hook替换掉signatures的值

public class HookApplication extends Application implements InvocationHandler {
    private static final int GET_SIGNATURES = 64;
    private String appPkgName = BuildConfig.FLAVOR;
    private Object base;
    private byte[][] sign;

    private void hook(Context context) {
        try {
            DataInputStream dataInputStream = new DataInputStream(new ByteArrayInputStream(Base64.decode("省略很长的签名 base64", 0)));
            byte[][] bArr = new byte[(dataInputStream.read() & 255)][];
            for (int i = 0; i < bArr.length; i++) {
                bArr[i] = new byte[dataInputStream.readInt()];
                dataInputStream.readFully(bArr[i]);
            }
            Class cls = Class.forName("android.app.ActivityThread");
            Object invoke = cls.getDeclaredMethod("currentActivityThread", new Class[0]).invoke(null, new Object[0]);
            Field declaredField = cls.getDeclaredField("sPackageManager");
            declaredField.setAccessible(true);
            Object obj = declaredField.get(invoke);
            Class cls2 = Class.forName("android.content.pm.IPackageManager");
            this.base = obj;
            this.sign = bArr;
            this.appPkgName = context.getPackageName();
            Object newProxyInstance = Proxy.newProxyInstance(cls2.getClassLoader(), new Class[]{cls2}, this);
            declaredField.set(invoke, newProxyInstance);
            PackageManager packageManager = context.getPackageManager();
            Field declaredField2 = packageManager.getClass().getDeclaredField("mPM");
            declaredField2.setAccessible(true);
            declaredField2.set(packageManager, newProxyInstance);
            System.out.println("PmsHook success.");
        } catch (Exception e) {
            System.err.println("PmsHook failed.");
            e.printStackTrace();
        }
    }

    /* access modifiers changed from: protected */
    public void attachBaseContext(Context context) {
        hook(context);
        super.attachBaseContext(context);
    }

    public Object invoke(Object obj, Method method, Object[] objArr) throws Throwable {
        if ("getPackageInfo".equals(method.getName())) {
            String str = objArr[0];
            if ((objArr[1].intValue() & 64) != 0 && this.appPkgName.equals(str)) {
                PackageInfo packageInfo = (PackageInfo) method.invoke(this.base, objArr);
                packageInfo.signatures = new Signature[this.sign.length];
                for (int i = 0; i < packageInfo.signatures.length; i++) {
                    packageInfo.signatures[i] = new Signature(this.sign[i]);
                }
                return packageInfo;
            }
        }
        return method.invoke(this.base, objArr);
    }
}

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去除签名校验的应对措施 [5] (opens new window)：
- 检查Application
- 在调用attachBaseContext之前检测签名
- 检查IPackageManager有没有被动态代理
- 使用别的API获取Package信息

暂无内容

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# 第四十二周ARTS总结

# Algorithm

# Review

# Tip

# Share