convert Object[] from stream to byte[]

Question

I try to filter a byte[], I want to remove line breaks from the stream

byte[] data = "y\neahbabydoit\nsothisistheway\ntodoit".getBytes();
Object[] tmp = IntStream.range(0, data.length).mapToObj(idx -> Integer.valueOf(data[idx]).byteValue()).filter(i -> i != 10).toArray();
System.out.println("src:"+Arrays.toString(data));
System.out.println("dst:"+Arrays.toString(tmp));

//works not!!
byte[] dest = (Byte[]) tmp; //help me here

The result (as expected) works (so far) but I'm not able to convert the result (Object[]) in an easy way back (to byte[])...

src:[121, 10, 101, 97, 104, 98, ...
dst:[121, 101, 97, 104, 98, 97, ...

I know there are ways to solve this problem (see How to convert int[] to byte[]) but I want to do it in an easy (stream-like) way...

any news from java 8 or later?

keep in mind that `\n` is not the only line separator – Patrick Parker Jul 06 '18 at 19:17 — Patrick Parker, Jul 06 '18 at 19:17

score 2 · Answer 1 · answered Jul 06 '18 at 18:32

2

To save yourself the hassle of handling multi-byte characters, it may be a lot easier to just handle the stream of characters:

String result =
    data.chars()
        .filter(c -> c != '\n')
        .mapToObj(c -> String.valueOf((char) c))
        .collect(Collectors.joining());

answered Jul 06 '18 at 18:32

Mureinik

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Or just `data.replace("\n", "");` – Jacob G. Jul 06 '18 at 19:04
2

@JacobG. better for the general task of “removing linebreaks” would be `data.replaceAll("\\R", "");` – Holger Jul 07 '18 at 13:33
@Holger Right but `data.replace("\n", "")` will not work either as it is not a String but a `byte[]`. Or else : `new String(data, StandardCharsets.UTF_8).replace(...)` – davidxxx Jul 07 '18 at 13:40
2

@davidxxx if `data` was a `byte[]`, there was no `chars()` method either. Both, this answer and JacobG’s comment use the fact that the OP initially had a `String` before querying the byte array. The answer also recommends processing characters instead of bytes. – Holger Jul 07 '18 at 13:43
@ Holger Ah okiiiiiii. I didn't get it. It is clear now. Thanks. – davidxxx Jul 07 '18 at 13:44

score 2 · Accepted Answer · edited Jul 06 '18 at 19:15

2

As @Mureinik suggested, it is better to deal with characters rather than bytes, to answer your question, you can certainly use something like

Byte[] tmp = IntStream.range(0, data.length)
        .mapToObj(idx -> Integer.valueOf(data[idx]).byteValue())
        .filter(i -> i != 10)
        .toArray(Byte[]::new);

edited Jul 06 '18 at 19:15

Patrick Parker

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answered Jul 06 '18 at 18:42

RP-

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`.mapToObj(idx -> Integer.valueOf(data[idx]).byteValue())` will read a `byte` from the array, convert it to an `Integer` object, extract its value as `byte`, followed by boxing it into a `Byte`. It’s much simpler to use just `.mapToObj(idx -> data[idx])`, which reads a `byte` from the array and boxes it into a `Byte`. – Holger Jul 07 '18 at 13:31

davidxxx · Answer 3 · 2018-07-10T19:05:45.737

Collecting to a byte array is not straight with Java 8.
But by using ByteArrayOutputStream::new as supplier in the collect operation you can.
It is a little more verbose because of the checked exception handling in the body lambda because of the combiner but it also has some advantages : it doesn't perform any boxing byte to Byte and it doesn't create unnecessary variables.

byte[] data = "y\neahbabydoit\nsothisistheway\ntodoit".getBytes();
byte[] dest = IntStream.range(0, data.length)
                       .map(i -> data[i])
                       .filter(i -> i != 10)
                       .collect(ByteArrayOutputStream::new, ByteArrayOutputStream::write, (bos1, bos2) -> {
                           try {
                               bos2.writeTo(bos1);
                           } catch (IOException e) {
                              throw new RuntimeException(e);
                           }
                       })
                       .toByteArray();

System.out.println("src:" + Arrays.toString(data));
System.out.println("dst:" + Arrays.toString(dest));

Output :

src:[121, 10, 101, 97, 104, 98, 97, 98, 121, ...]

dst:[121, 101, 97, 104, 98, 97, 98, 121,...]

You don’t need the type cast in `(bos, i) -> bos.write((byte) i)`, so you could even use `ByteArrayOutputStream::write`… — Holger, Jul 09 '18 at 11:14

convert Object[] from stream to byte[]

3 Answers3