Android文件操作代码示例,sd卡数据储存

1.

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    /**
     * 读取文件
     */
    public void readFile(View view) {// 很多初学者都会犯的错误
        try {
            FileInputStream fis = openFileInput("file.txt");
            byte[] bytes = new byte[20];
            fis.read(bytes);
            System.out.println("content:" + new String(bytes));
            fis.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 写入文件
     */
    public void writeFile(View view) {
        // 创建一个文件，程序自身可以读写
        try {
            FileOutputStream fos = openFileOutput("file.txt", Context.MODE_PRIVATE);
            fos.write("data".getBytes());
            fos.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2.模仿QQ登入,记住用户是写入文件

package com.glsite.qqloging;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStreamReader;

public class MainActivity extends AppCompatActivity {

    private EditText mEtnumber;
    private EditText mEtpassword;
    private CheckBox mMcbRemember;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // 1.找到界面上的控件
        // 2.点击按钮，将用户输入的用户名和密码保存到文件当中
        // 3.如果说下次启动app，那么就从文件当中读取出来显示到编辑框

        mEtnumber = findViewById(R.id.et_qqnumber);//ctrl+alt+f
        mEtpassword = findViewById(R.id.et_password);
        mMcbRemember = findViewById(R.id.cb_remember);
        restoreInfo();
    }
    /**
     * 根据原来保存的文件信息，把QQ号码和密码信息显示到界面
     */
    private void restoreInfo()  {
        File file = new File(this.getFilesDir(), "info.txt");
        try {
            if (file.exists()&&file.length()>0) {
                FileInputStream fileInputStream = new FileInputStream(file);
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(fileInputStream));
                String s = bufferedReader.readLine();
                String[] split = s.split("##");
                mEtnumber.setText(split[0]);
                mEtpassword.setText(split[1]);
            } else {

            }


        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    /**
     * 登录按钮的点击事件
     *
     * @param view
     */
    public void login(View view) {
        String qq = mEtnumber.getText().toString().trim();//str_t
        String  password =  mEtpassword.getText().toString().trim();
        // 判断是否需要记录用户名和密码
        if(TextUtils.isEmpty(qq)||TextUtils.isEmpty(password)){
            Toast.makeText(this,"用户名或密码不能为空", Toast.LENGTH_SHORT).show();
        return;
        }else{


            //模拟登入
            if ("10000".equals(qq)&&"123456".equals(password)) {
                //判断是否不需要记住用户名或密码
                File file = new File(this.getFilesDir(), "info.txt");
                //判断用户是否勾选了记住用户
                if(mMcbRemember.isChecked()){
                    try {
                        FileOutputStream fileOutputStream = new FileOutputStream(file);
                        String info = qq + "##" +password;
                        fileOutputStream.write(info.getBytes());
                        fileOutputStream.close();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }else{
                    if (file.exists()) {
                        file.delete();//未勾选保存,删除保存的文件
                    }
                }
                Toast.makeText(this,"登入成功", Toast.LENGTH_SHORT).show();
                /*Toast.makeText(this,this.getFilesDir().getAbsolutePath(), Toast.LENGTH_SHORT).show();*/
            } else {
                Toast.makeText(this,"登入失败", Toast.LENGTH_SHORT).show();
            }
        }
    }
}

 

3.用户sd卡储存,注意需要配置权限,安卓6.0需要运行时权限

3.1运行时权限

package com.glsite.wriesd;

import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.widget.Toast;

/**
 * @author Admin
 * @version $Rev$
 * @des ${TODO}
 * @updateAuthor $Author$
 * @updateDes ${TODO}
 */
public class BaseActivity extends AppCompatActivity {
    //**************** Android M Permission (Android 6.0权限控制代码封装)
    private int permissionRequestCode = 88;
    private PermissionCallback permissionRunnable;

    public interface PermissionCallback {
        void hasPermission();

        void noPermission();
    }

    /**
     * Android M运行时权限请求封装
     *
     * @param permissionDes 权限描述
     * @param runnable      请求权限回调
     * @param permissions   请求的权限（数组类型），直接从Manifest中读取相应的值，比如Manifest.permission.WRITE_CONTACTS
     */
    public void performCodeWithPermission(@NonNull String permissionDes, PermissionCallback runnable, @NonNull String... permissions) {
        if (permissions == null || permissions.length == 0)
            return;
        //        this.permissionrequestCode = requestCode;
        this.permissionRunnable = runnable;
        if ((Build.VERSION.SDK_INT < Build.VERSION_CODES.M) || checkPermissionGranted(permissions)) {
            if (permissionRunnable != null) {
                permissionRunnable.hasPermission();
                permissionRunnable = null;
            }
        } else {
            //permission has not been granted.
            requestPermission(permissionDes, permissionRequestCode, permissions);
        }

    }

    private boolean checkPermissionGranted(String[] permissions) {
        boolean flag = true;
        for (String p : permissions) {
            if (ActivityCompat.checkSelfPermission(this, p) != PackageManager.PERMISSION_GRANTED) {
                flag = false;
                break;
            }
        }
        return flag;
    }

    private void requestPermission(String permissionDes, final int requestCode, final String[] permissions) {
        if (shouldShowRequestPermissionRationale(permissions)) {
            /*1. 第一次请求权限时，用户拒绝了，下一次：shouldShowRequestPermissionRationale()  返回 true，应该显示一些为什么需要这个权限的说明
            2.第二次请求权限时，用户拒绝了，并选择了“不在提醒”的选项时：shouldShowRequestPermissionRationale()  返回 false
            3. 设备的策略禁止当前应用获取这个权限的授权：shouldShowRequestPermissionRationale()  返回 false*/
            // Provide an additional rationale to the user if the permission was not granted
            // and the user would benefit from additional context for the use of the permission.
            // For example, if the request has been denied previously.

            //            Snackbar.make(getWindow().getDecorView(), requestName,
            //                    Snackbar.LENGTH_INDEFINITE)
            //                    .setAction(R.string.common_ok, new View.OnClickListener() {
            //                        @Override
            //                        public void onClick(View view) {
            //                            ActivityCompat.requestPermissions(BaseAppCompatActivity.this,
            //                                    permissions,
            //                                    requestCode);
            //                        }
            //                    })
            //                    .show();
            //如果用户之前拒绝过此权限，再提示一次准备授权相关权限
            new AlertDialog.Builder(this)
                    .setTitle("提示")
                    .setMessage(permissionDes)
                    .setPositiveButton("授权", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            ActivityCompat.requestPermissions(BaseActivity.this, permissions, requestCode);
                        }
                    }).show();

        } else {
            // Contact permissions have not been granted yet. Request them directly.
            ActivityCompat.requestPermissions(BaseActivity.this, permissions, requestCode);
        }
    }

    private boolean shouldShowRequestPermissionRationale(String[] permissions) {
        boolean flag = false;
        for (String p : permissions) {
            if (ActivityCompat.shouldShowRequestPermissionRationale(this, p)) {
                flag = true;
                break;
            }
        }
        return flag;
    }

    /**
     * Callback received when a permissions request has been completed.
     */
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions,
                                           @NonNull int[] grantResults) {
        if (requestCode == permissionRequestCode) {
            if (verifyPermissions(grantResults)) {
                if (permissionRunnable != null) {
                    permissionRunnable.hasPermission();
                    permissionRunnable = null;
                }
            } else {
                Toast.makeText(this, "暂无权限执行相关操作！", Toast.LENGTH_SHORT).show();
                if (permissionRunnable != null) {
                    permissionRunnable.noPermission();
                    permissionRunnable = null;
                }
            }
        } else {
            super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        }

    }

    public boolean verifyPermissions(int[] grantResults) {
        // At least one result must be checked.
        if (grantResults.length < 1) {
            return false;
        }

        // Verify that each required permission has been granted, otherwise return false.
        for (int result : grantResults) {
            if (result != PackageManager.PERMISSION_GRANTED) {
                return false;
            }
        }
        return true;
    }
    //********************** END Android M Permission ****************************************
}

3.2

package com.glsite.wriesd;

import android.Manifest;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;

public class MainActivity extends BaseActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void click(View view) {
performCodeWithPermission("写入文件权限", new PermissionCallback() {
    @Override
    public void hasPermission() {
        //判断sd卡是否挂载
        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
            Toast.makeText(MainActivity.this, "sd卡已经挂载", Toast.LENGTH_SHORT).show();
            File sdfile = Environment.getExternalStorageDirectory();
            long freeSpace = sdfile.getFreeSpace();//获取储存空间
            if (freeSpace > 5 * 1024 * 1024) {
                File file = new File(sdfile, System.currentTimeMillis() + "hlw.3gp");
                try {
                    FileOutputStream fileOutputStream = new FileOutputStream(file);
                    byte[] bytes = new byte[1024];
                    for (int i = 0; i < 5 * 1024; i++) {
                        fileOutputStream.write(bytes);
                    }
                    fileOutputStream.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            } else {
                Toast.makeText(MainActivity.this, "内部空间不足", Toast.LENGTH_SHORT).show();
            }
        } else {
            Toast.makeText(MainActivity.this, "没有挂载", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void noPermission() {
Toast.makeText(MainActivity.this,"用户未授权", Toast.LENGTH_SHORT).show();
    }
}, Manifest.permission.WRITE_EXTERNAL_STORAGE);
        
    }
}

3.3 配置权限

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

4.权限机制

-rwxrw-r‐-1 root root 1213 Feb 2 09:39 abc

- 10个字符确定不同用户能对文件干什么

- 第一个字符代表文件（-）、目录（d），链接（l）

- 其余字符每3个一组（rwx），读（r）、写（w）、执行（x）

- 第一组rwx：文件所有者的权限是读、写和执行

- 第二组rw-：与文件所有者同一组的用户的权限是读、写但不能执行

- 第三组r--：不与文件所有者同组的其他用户的权限是读不能写和执行

也可用数字表示为：r=4，w=2，x=1  因此rwx=4+2+1=7


- 1 表示连接的文件数

- root 表示用户

- root表示用户所在的组

- 1213 表示文件大小（字节）

- Feb 2 09:39 表示最后修改日期

- abc 表示文件名

5.文件操作的两种模式

Context.MODE_PRIVATE：为默认操作模式，代表该文件是私有数据，只能被应用本身访问，在该模式下，写入的内容会覆盖原文件的内容，如果想把新写入的内容追加到原文件中。可以使用Context.MODE_APPEND
Context.MODE_APPEND：模式会检查文件是否存在，存在就往文件追加内容，否则就创建新文件。