本文目錄

sdcard文件讀寫

Android文件讀寫概述

在Androi中文件讀寫一共有以下目錄

raw目錄
asserts目錄
data/data/包名
sdcard目錄

其中raw下的和asserts下的文件可以以資源文件的形式讀取，這些目錄的數據只能讀取，不能寫入，兩者目錄下的文件在打包後會原封不動的保存在apk包中，不會被編譯成二進制。
data/data/包名和sdcard目錄文件可讀可寫。其中data/data/包名目錄不需要申請權限,sdcard目錄需要申請權限

讀取raw目錄文件

Android工程默認是沒有raw文件夾的在讀文件前我們先把raw 文件夾以及文件建好

點中工程的res目錄右鍵New -> Directory -> 彈窗中輸入raw
點中剛剛新建的raw目錄右鍵New -> File -> 彈窗中輸入test.txt
點開剛剛新建的test.txt文件，往裏面輸入hello world

讀數據方法

   InputStream inputStream = null;
   Reader reader = null;
    BufferedReader bufferedReader = null;
    try {
        //得到資源中的Raw數據流
        inputStream = getResources().openRawResource(R.raw.test);
        reader = new InputStreamReader(inputStream);// 字符流
        bufferedReader = new BufferedReader(reader); //緩衝流
        StringBuilder result = new StringBuilder();
        String temp;
        while ((temp = bufferedReader.readLine()) != null) {
            result.append(temp);
        }
        Log.i("MainActivity", "result:" + result);

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (reader != null) {
            try {
                reader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (inputStream != null) {
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (bufferedReader != null) {
            try {
                bufferedReader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }

從打印的結果中我們可以看出數據讀取成功

讀取assets目錄文件

Android工程默認是沒有assets文件夾的，在讀文件前我們先把assets 文件夾以及文件建好

點中工程右鍵New -> Folder -> Assets Folder
點中剛剛新建的Assets Folde目錄右鍵New -> File -> 彈窗中輸入test.txt
點開剛剛新建的test.txt文件，往裏面輸入hello world
讀去assets文件中的數據方法

		InputStream inputStream = null;
        Reader reader = null;
        BufferedReader bufferedReader = null;
        try {
            //得到資源中的asset數據流
            inputStream = getResources().getAssets().open("test.txt");
            reader = new InputStreamReader(inputStream);// 字符流
            bufferedReader = new BufferedReader(reader); //緩衝流
            StringBuilder result = new StringBuilder();
            String temp;
            while ((temp = bufferedReader.readLine()) != null) {
                result.append(temp);
            }
            Log.i("MainActivity", "result:" + result);

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (bufferedReader != null) {
                try {
                    bufferedReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        }

從打印的結果中我們可以看出數據讀取成功

data/data/(包名) 目錄文件讀寫

將數據以普通文件的形式保存在 /data/data/包名中，該方法不需要申請權限。
存放在數據區(/data/data/包名)的文件可以使用openFileOutput和openFileInput進行操作。
也可以直接指定文件/data/data/包名路徑讀寫。

該目錄存放文件類型規則如下：

路徑	功能
`data/data/包名/shared_prefs`	存放SharedPreferences數據
`data/data/包名/databases`	存放數據庫數據
`data/data/包名/files`	存放普通數據
`data/data/包名/cache`	存放緩存文件

寫數據

方法1：openFileOutput

        FileOutputStream fileOutputStream = null;
        try {
            String text = "hello world";
            fileOutputStream = openFileOutput("test.txt", MODE_PRIVATE);
            fileOutputStream.write(text.getBytes());
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fileOutputStream != null) {
                try {
                    fileOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

openFileOutput方法參數詳解

	@Override
    public FileOutputStream openFileOutput(String name, int mode)
        throws FileNotFoundException {
        
    }

name 存儲文件名字
mode 存儲方式 其值的含義如下

參數值	參數含義
Context.MODE_PRIVATE	指定該文件數據只能被本應用程序讀、寫
Context.MODE_WORLD_READABLE	指定該文件數據能被其他應用程序讀，但不能寫
Context.MODE_WORLD_WRITEABLE	指定該文件數據能被其他應用程序讀
Context.MODE_APPEND	該模式會檢查文件是否存在，存在就往文件追加內容，否則就創建新文件；

方法2：傳統方法讀寫

   String text = "hello world";
   File file1=new File("/data/data/com.lucashu.file/","test.txt");
      FileOutputStream fileOutputStream = null;
     try {
         fileOutputStream = new FileOutputStream(file1);
         fileOutputStream.write(text.getBytes());
     } catch (Exception e) {
         e.printStackTrace();
     }finally {
         if (fileOutputStream != null) {
             try {
                 fileOutputStream.close();
             } catch (IOException e) {
                 e.printStackTrace();
             }
         }
     }

執行以後我們可以看到添加了一個文件

讀數據

方法1：openFileInput

		FileInputStream fileInputStream = null;
        Reader reader = null;
        BufferedReader bufferedReader = null;
        try {
            fileInputStream = openFileInput("test.txt");
            reader = new InputStreamReader(fileInputStream);// 字符流
            bufferedReader = new BufferedReader(reader); //緩衝流
            StringBuilder result = new StringBuilder();
            String temp;
            while ((temp = bufferedReader.readLine()) != null) {
                result.append(temp);
            }
            Log.i("MainActivity", "result:" + result);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fileInputStream != null) {
                try {
                    fileInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (bufferedReader != null) {
                try {
                    bufferedReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

方法2：openFileInput

		InputStream inputStream = null;
        Reader reader = null;
        BufferedReader bufferedReader = null;
        try {

            File file=new File("/data/data/com.lucashu.file/", "test.txt");
            inputStream = new FileInputStream(file);
            reader = new InputStreamReader(inputStream);
            bufferedReader = new BufferedReader(reader);
            StringBuilder result = new StringBuilder();
            String temp;
            while ((temp = bufferedReader.readLine()) != null) {
                result.append(temp);
            }
            Log.i("MainActivity", "result:" + result);

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (bufferedReader != null) {
                try {
                    bufferedReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        }

從打印的結果中我們可以看出數據讀取成功

我們也可以用一下方法來獲取改文件的路徑

getFilesDir();// data/data/包名/files 目錄
getFilesDir().getParent(),;// data/data/包名/ 目錄

sdcard文件讀寫

sdcard讀寫的數據將數據保存在 /mnt/sdcard目錄,該目錄讀寫需要先申請動態權限，動態權限申請方法如下

申請動態權限

首先需要在manifest.xml中添加權限

<!--文件讀寫權限-->
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
 <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

如果是AndroidQ 或者更高的版本還需要在manifest.xml文件中的application節點下加入
android:requestLegacyExternalStorage="true"
申請動態權限方法：

private static final int REQUEST_EXTERNAL_STORAGE = 1;
private static String[] PERMISSIONS_STORAGE = {"android.permission.READ_EXTERNAL_STORAGE",
            "android.permission.WRITE_EXTERNAL_STORAGE"};

private void checkPermission() {
//檢查權限（NEED_PERMISSION）是否被授權 PackageManager.PERMISSION_GRANTED表示同意授權
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
            != PackageManager.PERMISSION_GRANTED) {
        if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission
                .WRITE_EXTERNAL_STORAGE)) {
            Toast.makeText(this, "請開通相關權限，否則無法正常使用本應用！", Toast.LENGTH_SHORT).show();
        }
        //申請權限
        ActivityCompat.requestPermissions(this, PERMISSIONS_STORAGE, REQUEST_EXTERNAL_STORAGE);

    } else {
        Toast.makeText(this, "已授權成功！", Toast.LENGTH_SHORT).show();
        writeSdcard();

    }
}

Activity中動態權限的回調方法

@Override
public void onRequestPermissionsResult(int requestCode,
                                       String permissions[], int[] grantResults) {
    switch (requestCode) {
        case REQUEST_EXTERNAL_STORAGE: {
            if (grantResults.length > 0
                    && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                Toast.makeText(this, "授權成功！", Toast.LENGTH_SHORT).show();
                writeSdcard();
            } else {
                Toast.makeText(this, "授權被拒絕！", Toast.LENGTH_SHORT).show();


            }
            return;
        }

    }
}

寫數據

private void writeSdcard()  {
        String text = "hello world";
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                File storage = Environment.getExternalStorageDirectory();
                File tmepfile = new File(storage.getPath());
                if (! tmepfile.exists()) {
                    tmepfile.mkdirs();
                }
                File file1=new File(tmepfile,"test.txt");
                if (!file1.exists()){
                    try {
                        file1.createNewFile();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                FileOutputStream fileOutputStream = null;
                try {
                    fileOutputStream = new FileOutputStream(file1);
                    fileOutputStream.write(text.getBytes());
                } catch (Exception e) {
                    e.printStackTrace();
                }finally {
                    if (fileOutputStream != null) {
                        try {
                            fileOutputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    }

執行以後我們可以看到添加了一個文件

讀數據

private void readSdcard() {
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                InputStream inputStream = null;
                Reader reader = null;
                BufferedReader bufferedReader = null;
                try {
                    File storage = Environment.getExternalStorageDirectory();
                    File tmepfile = new File(storage.getPath());
                    File file=new File(tmepfile, "test.txt");
                    inputStream = new FileInputStream(file);
                    reader = new InputStreamReader(inputStream);
                    bufferedReader = new BufferedReader(reader);
                    StringBuilder result = new StringBuilder();
                    String temp;
                    while ((temp = bufferedReader.readLine()) != null) {
                        result.append(temp);
                    }
                    Log.i("MainActivity", "result:" + result);

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (reader != null) {
                        try {
                            reader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (inputStream != null) {
                        try {
                            inputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (bufferedReader != null) {
                        try {
                            bufferedReader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }

                }
            }
        }
    }

sdcard文件讀寫完整代碼

package com.lucashu.file;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
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.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.Writer;

public class MainActivity extends AppCompatActivity {

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


    private void writeSdcard()  {
        String text = "hello world";
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                File storage = Environment.getExternalStorageDirectory();
                File tmepfile = new File(storage.getPath());
                if (! tmepfile.exists()) {
                    tmepfile.mkdirs();
                }
                File file1=new File(tmepfile,"test.txt");
                if (!file1.exists()){
                    try {
                        file1.createNewFile();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                FileOutputStream fileOutputStream = null;
                try {
                    fileOutputStream = new FileOutputStream(file1);
                    fileOutputStream.write(text.getBytes());
                } catch (Exception e) {
                    e.printStackTrace();
                }finally {
                    if (fileOutputStream != null) {
                        try {
                            fileOutputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    }


    private void readSdcard() {
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                InputStream inputStream = null;
                Reader reader = null;
                BufferedReader bufferedReader = null;
                try {
                    File storage = Environment.getExternalStorageDirectory();
                    File tmepfile = new File(storage.getPath());
                    File file=new File(tmepfile, "test.txt");
                    inputStream = new FileInputStream(file);
                    reader = new InputStreamReader(inputStream);
                    bufferedReader = new BufferedReader(reader);
                    StringBuilder result = new StringBuilder();
                    String temp;
                    while ((temp = bufferedReader.readLine()) != null) {
                        result.append(temp);
                    }
                    Log.i("MainActivity", "result:" + result);

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (reader != null) {
                        try {
                            reader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (inputStream != null) {
                        try {
                            inputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (bufferedReader != null) {
                        try {
                            bufferedReader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }

                }
            }
        }
    }
    private static final int REQUEST_EXTERNAL_STORAGE = 1;
    private static String[] PERMISSIONS_STORAGE = {"android.permission.READ_EXTERNAL_STORAGE",
            "android.permission.WRITE_EXTERNAL_STORAGE"};

    private void checkPermission() {
        //檢查權限（NEED_PERMISSION）是否被授權 PackageManager.PERMISSION_GRANTED表示同意授權
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission
                    .WRITE_EXTERNAL_STORAGE)) {
                Toast.makeText(this, "請開通相關權限，否則無法正常使用本應用！", Toast.LENGTH_SHORT).show();
            }
            //申請權限
            ActivityCompat.requestPermissions(this, PERMISSIONS_STORAGE, REQUEST_EXTERNAL_STORAGE);

        } else {
            Toast.makeText(this, "已授權成功！", Toast.LENGTH_SHORT).show();
            readSdcard();

        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        switch (requestCode) {
            case REQUEST_EXTERNAL_STORAGE: {
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    Toast.makeText(this, "授權成功！", Toast.LENGTH_SHORT).show();
                    readSdcard();
                } else {
                    Toast.makeText(this, "授權被拒絕！", Toast.LENGTH_SHORT).show();

                }
                return;
            }

        }
    }

}

Android 文件讀寫最全解析

本文目錄

Android文件讀寫概述

讀取raw目錄文件

讀取assets目錄文件

data/data/(包名) 目錄文件讀寫

寫數據

讀數據

sdcard文件讀寫

申請動態權限

寫數據

讀數據

sdcard文件讀寫完整代碼

maven 環境變量和倉庫配置

Google Hacking使用詳解

Android SQlite數據庫使用詳解

Android SDK環境變量配置權威指南

Android 動態權限最全解析

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