Java中整形和byte数组相互转换，支持正负数

/**
* 字节数组转int,适合转高位在前低位在后的byte[]
*
* @param bytes
* @return
*/
public static long byteArrayToLong(byte[] bytes) {
ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
DataInputStream dis = new DataInputStream(bais);
long result = 0;
try {
int len = dis.available();
if (len == 1) {
result = dis.readByte();
} else if (len == 2) {
result = dis.readShort();
} else if (len == 4) {
result = dis.readInt();
} else if (len == 8) {
result = dis.readLong();
}
} catch (IOException e) {
SyncLogUtil.e(e);
} finally {
try {
dis.close();
bais.close();
} catch (IOException e) {
SyncLogUtil.e(e);
}
}
return result;
}

/**
* int转byte[]，高位在前低位在后
*
* @param value
* @return
*/
public static byte[] varIntToByteArray(long value) {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream oos = new DataOutputStream(baos);
Long l = new Long(value);
try {
if (l == l.byteValue()) {
oos.writeByte(l.byteValue());
} else if (l == l.shortValue()) {
oos.writeShort(l.shortValue());
} else if (l == l.intValue()) {
oos.writeInt(l.intValue());
} else if (l == l.longValue()) {
oos.writeLong(l.longValue());
} else if (l == l.floatValue()) {
oos.writeFloat(l.floatValue());
} else if (l == l.doubleValue()) {
oos.writeDouble(l.doubleValue());
}
} catch(IOException e) {
SyncLogUtil.e(e);
} finally {
try {
baos.close();
oos.close();
} catch (IOException e) {
SyncLogUtil.e(e);
}
}
return baos.toByteArray();
}

/**
* 字节数组转int,适合转高位在前低位在后的byte[]
*
* @param bytes
* @return
*/
public static long byteArrayToLong(byte[] bytes) {
long result = 0;
int len = bytes.length;
if (len == 1) {
byte ch = (byte) (bytes[0] & 0xff);
result = ch;
} else if (len == 2) {
int ch1 = bytes[0] & 0xff;
int ch2 = bytes[1] & 0xff;
result = (short) ((ch1 << 8) | (ch2 << 0));
} else if (len == 4) {
int ch1 = bytes[0] & 0xff;
int ch2 = bytes[1] & 0xff;
int ch3 = bytes[2] & 0xff;
int ch4 = bytes[3] & 0xff;
result = (int) ((ch1 << 24) | (ch2 << 16) | (ch3 << 8) | (ch4 << 0));
} else if (len == 8) {
long ch1 = bytes[0] & 0xff;
long ch2 = bytes[1] & 0xff;
long ch3 = bytes[2] & 0xff;
long ch4 = bytes[3] & 0xff;
long ch5 = bytes[4] & 0xff;
long ch6 = bytes[5] & 0xff;
long ch7 = bytes[6] & 0xff;
long ch8 = bytes[7] & 0xff;
result = (ch1 << 56) | (ch2 << 48) | (ch3 << 40) | (ch4 << 32) | (ch5 << 24) | (ch6 << 16) | (ch7 << 8) | (ch8 << 0);
}
return result;
}

/**
* int转byte[]，高位在前低位在后
*
* @param value
* @return
*/
public static byte[] varIntToByteArray(long value) {
Long l = new Long(value);
byte[] valueBytes = null;
if (l == l.byteValue()) {
valueBytes = toBytes(value, 1);
} else if (l == l.shortValue()) {
valueBytes = toBytes(value, 2);
} else if (l == l.intValue()) {
valueBytes = toBytes(value, 4);
} else if (l == l.longValue()) {
valueBytes = toBytes(value, 8);
}
return valueBytes;
}

private static byte[] toBytes(long value, int len) {
byte[] valueBytes = new byte[len];
for (int i = 0;i < len;i++) {
valueBytes[i] = (byte) (value >>> 8 * (len - i - 1));
}
return valueBytes;
}

private static void check(long s, long r, String tag) {
if (s == r) {
System.out.println(tag + "[result:" + r + "]");
} else {
System.err.println(tag + "[source:" + s + ",result:" + r + "]");
}
}

public static void main(String[] args) throws Exception {
// byte
byte bMax = Byte.MAX_VALUE;
byte bMin = Byte.MIN_VALUE;
long b_max_v = byteArrayToLong(varIntToByteArray(bMax));
check(bMax, b_max_v, "byte");
long b_min_v = byteArrayToLong(varIntToByteArray(bMin));
check(bMin, b_min_v, "byte");

// short
short sMax = Short.MAX_VALUE;
short sMin = Short.MIN_VALUE;
long s_max_v = byteArrayToLong(varIntToByteArray(sMax));
check(sMax, s_max_v, "short");
long s_min_v = byteArrayToLong(varIntToByteArray(sMin));
check(sMin, s_min_v, "short");

//int
int iMax = Integer.MAX_VALUE;
int iMin = Integer.MIN_VALUE;
long i_max_v = byteArrayToLong(varIntToByteArray(iMax));
check(iMax, i_max_v, "int");
long i_min_v = byteArrayToLong(varIntToByteArray(iMin));
check(iMin, i_min_v, "int");

// long
long lMax = Long.MAX_VALUE;
long lMin = Long.MIN_VALUE;
long l_max_v = byteArrayToLong(varIntToByteArray(lMax));
check(lMax, l_max_v, "long");
long l_min_v = byteArrayToLong(varIntToByteArray(lMin));
check(lMin, l_min_v, "long");
}