【Android先进】如何使用数据文件来保存程序

在程序，有许多方法来存储和检索数据，本文，它描述了如何使用文件系统来保存数据编程和读取操作

我直接写了一个帮助类，进行文件的写入和读取操作

/**
 * 用于在文件里保存程序数据
 *
 * @author zhaokaiqiang
 *
 */
public class FileHelper {

	private static final String TAG = "FileHelper";
	private Context mContext;

	FileHelper(Context _mContext) {
		mContext = _mContext;
	}

	// 在手机本地硬盘中保存信息
	public void save(String fileName, String content) {

		FileOutputStream fileOutputStream = null;
		try {
			fileOutputStream = mContext.openFileOutput(fileName,
					Context.MODE_PRIVATE);
			fileOutputStream.write(content.getBytes());

		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {

				if (fileOutputStream != null) {
					fileOutputStream.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

	// 读取手机硬盘中保存的文件
	public void read(String fileName) {
		FileInputStream fileInputStream = null;
		try {
			fileInputStream = mContext.openFileInput(fileName);
			int len = 0;
			byte[] buffer = new byte[1024];
			ByteArrayOutputStream byteArrayInputStream = new ByteArrayOutputStream();
			while ((len = fileInputStream.read(buffer)) != -1) {
				byteArrayInputStream.write(buffer, 0, len);
			}
			String string = new String(byteArrayInputStream.toByteArray());
			Log.d(TAG, string);
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (fileInputStream != null) {
				try {
					fileInputStream.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}

	}
}

注意：使用写入操作的时候。写入的内容会将上次写入的内容进行覆盖

写入的文件保存在/data/data/package name/files文件夹下，使用DDMS能够进行查看

例如以下图所看到的：

使用DDMS将文件导出。就可以查看内容

上面这些是将数据写入到我们的手机自带的存储空间里，假设想写入我们的SDCard，那么应该怎么做呢？

以下的写入到SDCard的操作

// save infomation in the SDCard
	public boolean saveToSDCard(String fileName, String content) {

		// judge weather the SDCard exits,and can be read and written
		if (!Environment.getExternalStorageState().equals(
				Environment.MEDIA_MOUNTED)) {
			return false;
		}

		FileOutputStream fileOutputStream = null;
		File file = new File(Environment.getExternalStorageDirectory(),
				fileName);
		try {
			fileOutputStream = new FileOutputStream(file);
			fileOutputStream.write(content.getBytes());
			return true;
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {

				if (fileOutputStream != null) {
					fileOutputStream.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		return false;
	}

以下是读取位于SDCard根文件夹下文件的操作方法

// read the file in the SDCard
	public String readFromSD(String fileName) {
		FileInputStream fileInputStream = null;
		File file = new File(Environment.getExternalStorageDirectory(),
				fileName);
		try {
			fileInputStream = new FileInputStream(file);
			int len = 0;
			byte[] buffer = new byte[1024];
			ByteArrayOutputStream byteArrayInputStream = new ByteArrayOutputStream();
			while ((len = fileInputStream.read(buffer)) != -1) {
				byteArrayInputStream.write(buffer, 0, len);
			}
			String string = new String(byteArrayInputStream.toByteArray());
			return string;
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (fileInputStream != null) {
				try {
					fileInputStream.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}

		return null;
	}

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