Java 8 Streams: IntStream to String [duplicate]

问题

In Java 8 streams API, calling chars() on any String object returns an IntStream object containing all the characters.

What would be the correct way to convert the returned IntStream object back to a String? Calling toArray() would give me an int[], which is not accepted by any of the String constructor.

回答1:

You can use toArray(), then the String(int[], int, int) constructor. This isn't entirely satisfactory as chars() is specified to return UTF-16 code units, basically:

Returns a stream of int zero-extending the char values from this sequence. Any char which maps to a surrogate code point is passed through uninterpreted.

Using codePoints() instead would be more in-keeping with this constructor, which expects code points rather than UTF-16 code units. Otherwise (with chars) if your original string does contain surrogate pairs, you may find you get an error - I haven't tried it, but it would make sense.

I don't know of a simple way of doing this without converting to an array first.

回答2:

using StringBuilder's appendCodePoint method would do the trick as well,

IntStream in = "Convert me to a String".codePoints();

String intStreamToString = in.collect(StringBuilder::new,
        StringBuilder::appendCodePoint, StringBuilder::append)
        .toString();

System.out.println(intStreamToString);

回答3:

I am pretty sure there must be many ways to do it, but another way is by using a StringWriter:

IntStream in = "It was the best of times".chars();
StringWriter sw = new StringWriter();
in.forEach(sw::write); 
System.out.println(sw.toString());

This all could also be expressed in a collector as:

IntStream in = "It was the best of times".chars();
String text = in.collect(
    StringWriter::new, 
    StringWriter::write, 
    (swl, swr) -> swl.write(swr.toString())).toString();
System.out.println(text);

回答4:

This is an other idea:

@Test
public void testIntStreamSequential() {
    final String testString = "testmesoftly";
    IntStream is = testString.chars();
    String result = is.collect(
        StringBuilder::new,
        (sb, i) -> sb.append((char)i),
        StringBuilder::append
        ).toString();
    assertEquals(testString, result);
}

@Test
public void testIntStreamParallel() {
    final String testString = "testmesoftly";
    IntStream is = testString.chars();
    String result = is.parallel().collect(
        StringBuilder::new,
        (sb, i) -> sb.append((char)i),
        StringBuilder::append
        ).toString();
    assertEquals(testString, result);
}

Note that using a dedicated Collector as proposed by @Lii is not very efficient, because of the boxing so you should use this three argument construct (thanks @holger)

来源：https://stackoverflow.com/questions/28280721/java-8-streams-intstream-to-string

标签

java

java-8

java-stream