Java: Conversion of String to byte array, then to long value and vice versa

Question

Basically, I'm looking for .NET's BitConverter.

I need to get bytes from String, then parse them to long value and store it. After that, read long value, parse to byte array and create original String. How can I achieve this in Java?

Edit: Someone did already ask similar question. I am looking more like for samples then javadoc reference ...

Why would you convert byte[] to long[] to store them. The problem is that long must be multiple of 8 bytes long, so if your string is not a multiple of 8, you will have to record the length as well. Why not save the byte[] as a byte[], this is the simplest and more efficient. — Peter Lawrey
– Peter Lawrey, Commented Dec 13, 2010 at 18:43
@The Elite Gentleman It's something that I did myself and wasn't able to figure out how to solve described problem though :) — Xorty
– Xorty, Commented Dec 13, 2010 at 18:49
@The javadoc, like most API documentation, is much better at answering "what does this do?" than it is at answering "how do I do this?". — Karl Knechtel
– Karl Knechtel, Commented Dec 13, 2010 at 18:57

Andrew · Accepted Answer · 2021-04-06 13:30:04Z

2

String has a getBytes method. You could use this to get a byte array.

To store the byte-array as longs, I suggest you wrap the byte-array in a ByteBuffer and use the asLongBuffer method.

To get the String back from an array of bytes, you could use the String(byte[] bytes) constructor.

String input = "hello long world";

byte[] bytes = input.getBytes();
LongBuffer tmpBuf = ByteBuffer.wrap(bytes).asLongBuffer();
    
long[] lArr = new long[tmpBuf.remaining()];
for (int i = 0; i < lArr.length; i++)
    lArr[i] = tmpBuf.get();
    
System.out.println(input);
System.out.println(Arrays.toString(lArr));
// store longs...
    
// ...load longs
long[] longs = { 7522537965568945263L, 7955362964116237412L };
byte[] inputBytes = new byte[longs.length * 8];
ByteBuffer bbuf = ByteBuffer.wrap(inputBytes);
for (long l : longs)
    bbuf.putLong(l);
System.out.println(new String(inputBytes));

Note that you probably want to store an extra integer telling how many bytes the long-array actually stores, since the number of bytes may not be a multiple of 8.

edited Apr 6, 2021 at 13:30

Andrew

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answered Dec 13, 2010 at 18:28

aioobe

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10 Comments

Xorty Over a year ago

And how do you get original string back from bytes?

Buhake Sindi Over a year ago

How would you parse the long back to byte array?

Xorty Over a year ago

what are those long numbers? if I change string to "Hello joe world" result is again "hello long world"

aioobe Over a year ago

I manually entered the numbers corresponding to "hello long world" to simulate a "load longs from disk" :-) You could replace longs = { ... with longs = lArr; instead to short-cut it :)

Xorty Over a year ago

OK, so let's get original string. I updated code to: long[] longs = lArr; With "hello long world" it works, with "hello joe world" it doesn't. Try it yourself :)

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