【Java 8 新特性】Java 8 Collectors：joining()使用示例

在本页中，我们将提供 java 8 Collectors joining()示例。方法返回收集器实例。它按顺序连接输入元素。我们也可以在元素连接中传递分隔符、前缀和后缀。

1.joining()方法说明

假设我们用以下方式收集元素A、B、C、D。

①

joining()

它返回用于连接不带分隔符的元素的收集器。对于给定的输入元素，输出字符串将是ABCD。

②

joining(CharSequence delimiter)

它返回用于将元素与给定分隔符连接起来的收集器。对于给定的输入元素和分隔符(-)，输出字符串将是A-B-C-D。

③

joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)

它返回收集器，该收集器用于连接具有给定分隔符、前缀和后缀的元素。对于给定的输入元素，分隔符( - )、前缀( [ )和后缀( ] )，输出字符串将是[A-B-C-D]。

2.使用Collectors.joining()方法拼接包含String类型的List

JoiningExampleWithListOfString.java

package com.concretepage;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class JoiningExampleWithListOfString {
     
    public static void main(String[] args) {
     
        List<String> list = Arrays.asList("Ram","Shyam","Shiv","Mahesh");
        String result=  list.stream().collect(Collectors.joining());
        System.out.println(result);
        result=  list.stream().collect(Collectors.joining(","));
        System.out.println(result);
        result=  list.stream().collect(Collectors.joining("-","[","]"));
        System.out.println(result);        
    }		
} 

输出

RamShyamShivMahesh
Ram,Shyam,Shiv,Mahesh
[Ram-Shyam-Shiv-Mahesh] 

2.使用Collectors.joining()方法拼接包含Object类型的List

JoiningExampleWithListOfObject.java

package com.concretepage;
import java.util.List;
import java.util.stream.Collectors;
public class JoiningExampleWithListOfObject {
     
    public static void main(String[] args) {
     
        List<Person> list = Person.getList();
        System.out.println("--Join person name--");
        String result=  list.stream().map(p -> p.getName()).collect(Collectors.joining());
        System.out.println(result);
        result=  list.stream().map(p -> p.getName()).collect(Collectors.joining("|"));
        System.out.println(result);
        result=  list.stream().map(p -> p.getName()).collect(Collectors.joining("-","[","]"));
        System.out.println(result);
        
        System.out.println("--Join person age--");
        result=  list.stream().map(p -> String.valueOf(p.getAge())).collect(Collectors.joining());
        System.out.println(result);
        result=  list.stream().map(p -> String.valueOf(p.getAge())).collect(Collectors.joining("|"));
        System.out.println(result);
        result=  list.stream().map(p -> String.valueOf(p.getAge())).collect(Collectors.joining("-","[","]"));
        System.out.println(result);       
        
        System.out.println("--Join person name-age--");
        result=  list.stream().map(p -> p.getName()+"-" + p.getAge()).collect(Collectors.joining("|"));
        System.out.println(result);
        result=  list.stream().map(p -> p.getName()+"-" + p.getAge()).collect(Collectors.joining("|","[","]"));
        System.out.println(result);        
    }		
} 

Person.java

package com.concretepage;
import java.util.ArrayList;
import java.util.List;
public class Person {
     
	private String name;
	private int age;
	public Person(String name, int age) {
     
		this.name = name;
		this.age = age;
	}
	public String getName() {
     
		return name;
	}
	public int getAge() {
     
		return age;
	}
	public static List<Person> getList() {
     
		List<Person> list = new ArrayList<>();
		list.add(new Person("Ram", 23));
		list.add(new Person("Shyam", 20));
		list.add(new Person("Shiv", 25));
		list.add(new Person("Mahesh", 30));
		return list;
	}
} 

输出

--Join person name--
RamShyamShivMahesh
Ram|Shyam|Shiv|Mahesh
[Ram-Shyam-Shiv-Mahesh]
--Join person age--
23202530
23|20|25|30
[23-20-25-30]
--Join person name-age--
Ram-23|Shyam-20|Shiv-25|Mahesh-30
[Ram-23|Shyam-20|Shiv-25|Mahesh-30] 

参考文献

【1】Java 8 Doc: Collectors
【2】Java 8 Collectors: joining() Example