Android(安卓)SDcard 文件读写，RandomAccessFile操作

SD Card 相关的权限：

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

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context="shortcut.song.com.myapplication.SDCardTestActivity">    <Button        android:id="@+id/btn_read_sdcard"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="read"/>    <Button        android:id="@+id/btn_write_sdcard"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="write"/>    <EditText        android:id="@+id/edit_1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:hint="read"/>    <EditText        android:id="@+id/edit_2"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:hint="write"/>LinearLayout>

package shortcut.song.com.myapplication;import android.os.Environment;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;import java.io.BufferedReader;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStreamReader;import java.io.RandomAccessFile;public class SDCardTestActivity extends AppCompatActivity {    private String FILE_NAME = "/sdandroid.bin";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_sdcard_test);        final Button read = (Button)findViewById(R.id.btn_read_sdcard);        final Button write = (Button)findViewById(R.id.btn_write_sdcard);        final EditText edit1 = (EditText)findViewById(R.id.edit_1);        final EditText edit2 = (EditText)findViewById(R.id.edit_2);        read.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                //将edit1输入的内容写到文件中                edit2.setText(read());            }        });        write.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                write(edit1.getText().toString());                edit1.setText("");            }        });    }    private String read() {        try {            //如果设置插入了SD卡，并且应用程序具有访问SD卡的权限            if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {                //获取SD卡对应的存储目录                File sdCardDir = Environment.getExternalStorageDirectory();                //获取指定文件对应的输入流                FileInputStream fis = new FileInputStream(sdCardDir.getCanonicalPath() + FILE_NAME);                //将指定的输入流包装成BufferedReader                BufferedReader br = new BufferedReader(new InputStreamReader(fis));                StringBuilder sb = new StringBuilder("");                String line = null;                //循环读取文件内容                while ( (line = br.readLine()) != null)                {                    sb.append(line);                }                //关闭资源                br.close();                return sb.toString();            }else{                Toast.makeText(SDCardTestActivity.this, "Not Find SD card.", Toast.LENGTH_LONG).show();            }        } catch (IOException e) {            e.printStackTrace();        }        return null;    }    private void write(String content) {        try {            //如果设置插入了SD卡，并且应用程序具有访问SD卡的权限            if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {                //获取SD卡对应的存储目录                File sdCardDir = Environment.getExternalStorageDirectory();                    File targetFile = new File(sdCardDir.getCanonicalPath() + FILE_NAME);                //以指定文件创建RandomAccessFile 对象                RandomAccessFile raf = new RandomAccessFile(targetFile, "rw");                //将文件记录移动到文件最后                raf.seek(targetFile.length());                //输出文件内容                raf.write(content.getBytes());                //关闭RandomAccessFile                raf.close();            }else{                Toast.makeText(SDCardTestActivity.this, "Not Find SD card.", Toast.LENGTH_LONG).show();            }        } catch (IOException e) {            e.printStackTrace();        }    }}

SD Card 相关的权限：

运行效果：

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