Android的SD卡文件读写操作

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读写SD卡上文件的步骤：

1.调用Environment的getExternalStorageState()　方法判断手机上是否插入了SD卡，并且应用程序具有读写权限

　　如：

//如果手机已插入SD卡,且应用程序具有读写SD卡的能力,下面语句返回true

Environment.getExternalstorageState().equals(Environment.MEDIA_MOUNTED)

2.调用Environment的getExternalStorageDirectory()方法来获取外部存储器,也就是SD卡的目录

3.判断要读写的文件所在目录是否存在，判断要读写的文件是否存在，若不存在则创建

4.使用FileInputStream,FileOutputStream,FileReader或FileWriter读，写SD卡里的文件

5.在 AndroidManifest.xml 中添加SD卡的读写权限

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

代码如下：

public class WriteReadFileAPI {    public static void write(String directory, String fileName, String content)      {          try          {              //如果手机插入了SD卡,而且应用程序具有访问SD的权限              if(Environment.getExternalStorageState()                      .equals(Environment.MEDIA_MOUNTED))              {                  //获取SD卡根目录                  File sdCardDir = Environment.getExternalStorageDirectory();                                  String directory_full_path = sdCardDir.getCanonicalPath()+"/"+directory;                String file_full_path = sdCardDir.getCanonicalPath()+"/"+directory+"/"+fileName;                                createDir(directory_full_path);                createFile(directory_full_path, fileName);                                File targetFile = new File(file_full_path);                                  System.out.println(file_full_path);                                //以指定文件创建RandomAccessFile对象                  RandomAccessFile raf = new RandomAccessFile(targetFile, "rw");                  //将文件记录指针移动到最后                  raf.seek(targetFile.length());                  //输出文件内容                  raf.write(content.getBytes());                  raf.close();                                              }          }          catch(Exception e)          {              e.printStackTrace();          }      }          public static String read(String directory, String fileName )      {          try          {              //如果手机插入了SD卡,而且应用程序具有访问SD的权限              if(Environment.getExternalStorageState()                      .equals(Environment.MEDIA_MOUNTED))              {                  //获取SD卡根目录                  File sdCardDir = Environment.getExternalStorageDirectory();                                  String file_full_path = sdCardDir.getCanonicalPath()+"/"+directory+"/"+fileName;                              System.out.println(file_full_path);                            //获取指定文件对应的输入流                  FileInputStream fis = new FileInputStream(file_full_path);                  //将指定输入流包装成BufferedReader                  BufferedReader br = new BufferedReader(new InputStreamReader(fis));                  StringBuilder sb = new StringBuilder("");                  String line = null;                  while((line = br.readLine()) != null)                  {                      sb.append(line);                  }                  return sb.toString();                 }          }          catch(Exception e)          {              e.printStackTrace();              return null;        }return null;      }          public static void createFile(String path,String filename) throws IOException    {        File file=new File(path+"/"+filename);        System.out.println(path);        System.out.println(filename);        System.out.println(path+"/"+filename);        if(!file.exists())            file.createNewFile();    }        public static void createDir(String path){        File dir=new File(path);        if(!dir.exists())            dir.mkdir();    }          }

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