【Stream流学习】Java 8 新特性｜Collectors.joining() 案例详解

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@[toc]

一、文章序言

业务场景：在项目中我们常常要对list集合的数据做一些字符串拼接/处理等相关操作

常见的案例如下

/**
 * @program: RecursionAlgorithm
 * @description: Java 8 新特性｜Collectors.joining()
 * @author: 辰兮要努力
 * @create: 2021-10-02 11:01
 */
public class StreamDemo {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("辰兮","2021","要努力");
        String result=  list.stream().collect(Collectors.joining());
        System.out.println(result);
    }
}

输出结果

辰兮2021要努力

Collectors.joining() 方法以遭遇元素的顺序拼接元素。我们可以传递可选的拼接字符串、前缀和后缀

分隔符：delimiter
前缀：prefix
后缀：suffix

二、案例实践

来一起学习一下相关的Collectors.joining() 方法

import java.util.Arrays;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * @program: RecursionAlgorithm
 * @description: Java 8 新特性｜Collectors.joining()
 * @author: 辰兮要努力
 * @create: 2021-10-02 11:01
 */
public class StreamDemo {
    public static void main(String[] args) {
        final String[] strings = {"x", "y", "z"};
        Stream<String> stream1 = Stream.of(strings);
        Stream<String> stream2 = Stream.of(strings);
        Stream<String> stream3 = Stream.of(strings);
        Stream<String> stream4 = Stream.of(strings);
        Stream<String> stream5 = Stream.of(strings);
        // 拼接成 [x, y, z] 
        String result1 = stream1.collect(Collectors.joining(", ", "[", "]"));
        // 拼接成 x | y | z 
        String result2 = stream2.collect(Collectors.joining(" | ", "", ""));
        // 拼接成 x -> y -> z] 
        String result3 = stream3.collect(Collectors.joining(" -> ", "", ""));
        //[x, y, z]
        System.out.println(result1);
        //x | y | z
        System.out.println(result2);
        //x -> y -> z
        System.out.println(result3);

        //[x.y.z]
        String result4 =  stream4.collect(Collectors.joining(".","[","]"));

        //xyz
//        String result4 =  stream4.collect(Collectors.joining(""));

        System.out.println(result4);
    }
}

输出结果

[x, y, z]
x | y | z
x -> y -> z
[x.y.z]

如上案例均可以在自己电脑实践

Java 8 流 ( stream ) 收集器 ( Collectors ) 中的 joining() 方法。该方法会返回一个 Collectors 实例，方便在流收集器上的链式操作

源码如下

 /**
     * Returns a {@code Collector} that concatenates the input elements,
     * separated by the specified delimiter, with the specified prefix and
     * suffix, in encounter order.
     *
     * @param delimiter the delimiter to be used between each element
     * @param  prefix the sequence of characters to be used at the beginning
     *                of the joined result
     * @param  suffix the sequence of characters to be used at the end
     *                of the joined result
     * @return A {@code Collector} which concatenates CharSequence elements,
     * separated by the specified delimiter, in encounter order
     */
    public static Collector<CharSequence, ?, String> joining(CharSequence delimiter,
                                                             CharSequence prefix,
                                                             CharSequence suffix) {
        return new CollectorImpl<>(
                () -> new StringJoiner(delimiter, prefix, suffix),
                StringJoiner::add, StringJoiner::merge,
                StringJoiner::toString, CH_NOID);
    }

希望如上的案例能帮助大家了解Collectors.joining() 的相关操作，更好的处理项目中不同的业务场景

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