Android实现读写SD卡

2019-12-12 06:25:27

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SD卡的读写是我们在开发Android 应用程序过程中最常见的操作。下面介绍SD卡的读写操作方式：

1. 获取SD卡的根目录

String  sdCardRoot = Environment.getExternalStorageDirectory().getAbsolutePath();   

2. 在SD卡上创建文件夹目录

/**  * 在SD卡上创建目录  */ public File createDirOnSDCard(String dir) {   File dirFile = new File(sdCardRoot + File.separator + dir +File.separator);   Log.v("createDirOnSDCard", sdCardRoot + File.separator + dir +File.separator);   dirFile.mkdirs();   return dirFile; }

3. 在SD卡上创建文件

/**  * 在SD卡上创建文件  */ public File createFileOnSDCard(String fileName, String dir) throws IOException {   File file = new File(sdCardRoot + File.separator + dir + File.separator + fileName);   Log.v("createFileOnSDCard", sdCardRoot + File.separator + dir + File.separator + fileName);   file.createNewFile();   return file; }

4.判断文件是否存在于SD卡的某个目录

/**  * 判断SD卡上文件是否存在  */ public boolean isFileExist(String fileName, String path) {   File file = new File(sdCardRoot + path + File.separator + fileName);   return file.exists(); }

5.将数据写入到SD卡指定目录文件

/* 写入数据到SD卡中    */   public File writeData2SDCard(String path, String fileName, InputStream data)   {     File file = null;     OutputStream output = null;          try {       createDirOnSDCard(path); //创建目录       file = createFileOnSDCard(fileName, path); //创建文件       output = new FileOutputStream(file);       byte buffer[] = new byte[2*1024];     //每次写2K数据       int temp;       while((temp = data.read(buffer)) != -1 )       {         output.write(buffer,0,temp);       }       output.flush();            } catch (Exception e) {       e.printStackTrace();     }     finally{       try {         output.close();  //关闭数据流操作       } catch (Exception e2) {         e2.printStackTrace();       }     }          return file;   }

注意事项

对SD卡的操作，必须要申请权限：

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

详情看这里 //www.VeVB.COm/article/34296.htm

注意：不直接进行读出是为了防止打文件操作对内存的消耗，所以用输入流读到硬盘上。

public String readFile(String fileName) throws Exception{    FileInputStream fis = context.openFileInput(fileName);    byte[] bytes = new byte[fis.available()];    fis.read(bytes);    fis.close();    return new String(bytes,"utf-8");  }

当文件很大的时候，byte[]会占用很大的内存。

package cn.itcast.fileio.service; import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream; import android.content.Context;import android.os.Environment; public class SdCardService {  private Context ctx;   public SdCardService(Context ctx) {    this.ctx = ctx;  }   /**   * 写文件入skcard   */  public void writeToSdCard(String fileName, String cont) {    try {      // 判断是否有挂载sdcard      if (Environment.getExternalStorageState().equals(          Environment.MEDIA_MOUNTED)) {        // 得到sdcar文件目录        File dir = Environment.getExternalStorageDirectory();        File file = new File(dir, "itcast.txt");        FileOutputStream fos = new FileOutputStream(file);        fos.write(cont.getBytes());        fos.close();      }    }    catch (Exception e) {      e.printStackTrace();    }  }  /**   * 读SdCard中的文件   */  public String readSdCard(String fileName) {    try {      // 判断是否有挂载sdcard      if (Environment.getExternalStorageState().equals(          Environment.MEDIA_MOUNTED)) {        // 得到sdcar文件目录        File dir = Environment.getExternalStorageDirectory();        File file = new File(dir, "itcast.txt");        FileInputStream fis = new FileInputStream(file);        return readIs2String(fis);      }    }    catch (Exception e) {      e.printStackTrace();    }    return null;  }     /**   * 将输入流数据读取到输出流当中   */  private OutputStream readIs2Os(InputStream is ,OutputStream os){    try {      byte[] bytes = new byte[1024];      int length = 0 ;      while((length = is.read(bytes)) != -1){        os.write(bytes, 0, length);      }      is.close();      os.close();    }    catch (IOException e) {      e.printStackTrace();    }    return os ;  }     /**   * 将输入流数据读取到输出流当中   */  public byte[] readIs2Bytes(InputStream is){    ByteArrayOutputStream baos = new ByteArrayOutputStream();    readIs2Os(is,baos);    return baos.toByteArray() ;  }     public String readIs2String(InputStream is){    try {      return new String(readIs2Bytes(is),"utf-8");    }    catch (Exception e) {      e.printStackTrace();    }    return null ;  }     public String readIs2String(String fileName){    try {      if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){        File dir = Environment.getExternalStorageDirectory();        File file = new File(dir,fileName);        FileInputStream is = new FileInputStream(file);        return readIs2String(is);      }    }    catch (Exception e) {      e.printStackTrace();    }    return null ;  }}

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