前言
在Android应用开发中，有时需要把一些内容以文件的方式保存到sdcard上，这时我们需要考虑数据的安全性，这就涉及到文件的加解密，这里简单介绍一种文件的加解密实现方法。
实现方案
我们在读写文件的时候，一般会用到FileInputStream和FileOutputStream,因此我们加解密的时机可以选在read和write数据时，这样很好的和上层业务隔离开，实现方法如下
- 实现加密算法
public class DataConvertUtil {
private static byte rotateLeft(byte sourceByte, int n) {
int temp = sourceByte & 0xFF;
return (byte) ((temp << n) | (temp >> (8 - n)));
}
private static byte rotateRight(byte sourceByte, int n) {
int temp = sourceByte & 0xFF;
return (byte) ((temp >> n) | (temp << (8 - n)));
}
private static byte[] rotateLeft(byte[] sourceBytes, int n) {
for (int i = 0; i < sourceBytes.length; i++) {
sourceBytes[i] = rotateLeft(sourceBytes[i], n);
}
return sourceBytes;
}
private static byte[] rotateRight(byte[] sourceBytes, int n) {
for (int i = 0; i < sourceBytes.length; i++) {
sourceBytes[i] = rotateRight(sourceBytes[i], n);
}
return sourceBytes;
}
public static byte[] encryData(byte[] buffer) {
return rotateLeft(buffer,3);
}
public static byte[] decryData(byte[] buffer) {
return rotateRight(buffer,3);
}
}
- 继承FileOutputStream
public class EncryOutputStream extends FileOutputStream {
public EncryOutputStream(String path) throws FileNotFoundException {
super(path);
}
@Override
public void write(byte[] buffer) throws IOException {
this.write(buffer, 0, buffer.length);
}
@Override
public void write(byte[] buffer, int byteOffset, int byteCount) throws IOException {
buffer = DataConvertUtil.encryData(buffer);
super.write(buffer, byteOffset, byteCount);
}
@Override
public void write(int oneByte) throws IOException {
byte[] buffer = new byte[1];
buffer[0] = (byte) oneByte;
this.write(buffer);
}
}
3.继承FileInputStream
public class EncryFileInputStream extends FileInputStream {
public EncryFileInputStream(String path) throws FileNotFoundException {
super(path);
}
@Override
public int read() throws IOException {
byte[] buffer = new byte[1];
this.read(buffer);
return buffer[0];
}
@Override
public int read(byte[] buffer) throws IOException {
return this.read(buffer, 0, buffer.length);
}
@Override
public int read(byte[] buffer, int byteOffset, int byteCount) throws IOException {
int length = super.read(buffer, byteOffset, byteCount);
DataConvertUtil.decryData(buffer);
return length;
}
}
