1.判断安装文件是否存在

private boolean fileIsExists(){
        boolean isExists=false;
        try{
            String fileName= Environment.getExternalStorageDirectory() +APKpath+apk_name;
            File file = new File(fileName);
            if(file.exists()){
                isExists = true;
            }
        }catch (Exception e) {
            // TODO: handle exception
        }
        return  isExists;
    }

2.自动安装

private void InstallAPK() {
        try {
            File file = new File(Environment.getExternalStorageDirectory()+APKpath, apk_name);
            if(!fileIsExists())
            {
                Toast.makeText(getApplicationContext(), "对不起，更新的文件找不到！",  Toast.LENGTH_SHORT).show();
                return ;
            }
            Intent intent = new Intent();
            //执行动作
            intent.setAction(Intent.ACTION_VIEW);
            //为这个新apk开启一个新的activity栈
            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            //执行的数据类型
            intent.setDataAndType(Uri.fromFile(file), "application/vnd.android.package-archive");
            //开始安装
            startActivity(intent);
            //关闭旧版本的应用程序的进程
           //android.os.Process.killProcess(android.os.Process.myPid());
        } catch (Exception e) {
            Log.e(TAG,"安装失败");
            e.printStackTrace();
        }
    }