Java 8 Map Filter 过滤示例

Java 8之前：

String result = ""; for (Map.Entry<Integer, String> entry : A_MAP_EXAMPLE.entrySet()) { if("something".equals(entry.getValue())){ result = entry.getValue(); } }

在Java 8中，您可以转换Map.entrySet()到stream由遵循filter()和collect()它。

//Map -> Stream -> Filter -> String String result = A_MAP_EXAMPLE.entrySet().stream() .filter(map -> "something".equals(map.getValue())) .map(map->map.getValue()) .collect(Collectors.joining());  //Map -> Stream -> Filter -> MAP Map<Integer, String> collect = A_MAP_EXAMPLE.entrySet().stream() .filter(map -> map.getKey() == 2) .collect(Collectors.toMap(p -> p.getKey(), p -> p.getValue()));

Java 8 – 过滤地图

一个过滤Map并返回String的完整示例。

TestMapFilter.java

package com.mkyong.java8  import java.util.HashMap; import java.util.Map; import java.util.stream.Collectors;  public class TestMapFilter {  public static void main(String[] args) {  Map<Integer, String> HOSTING = new HashMap<>(); HOSTING.put(1, "linode.com"); HOSTING.put(2, "heroku.com"); HOSTING.put(3, "digitalocean.com"); HOSTING.put(4, "aws.amazon.com");  String result = ""; for (Map.Entry<Integer, String> entry : HOSTING.entrySet()) { if ("aws.amazon.com".equals(entry.getValue())) { result = entry.getValue(); } } System.out.println("Before Java 8 : " + result);  //Map -> Stream -> Filter -> String result = HOSTING.entrySet().stream() .filter(map -> "aws.amazon.com".equals(map.getValue())) .map(map -> map.getValue()) .collect(Collectors.joining());  System.out.println("With Java 8 : " + result);  } }

Output

之前Java 8：aws.amazon.com
使用Java 8：aws.amazon.com

2. Java 8 – 过滤Map＃2

另一个过滤Map的例子，但这将返回一个Map。

TestMapFilter.java

package com.mkyong.java8  import java.util.HashMap; import java.util.Map; import java.util.stream.Collectors;  public class TestMap {  public static void main(String[] args) {  Map<Integer, String> HOSTING = new HashMap<>(); HOSTING.put(1, "linode.com"); HOSTING.put(2, "heroku.com"); HOSTING.put(3, "digitalocean.com"); HOSTING.put(4, "aws.amazon.com");  //Map -> Stream -> Filter -> Map Map<Integer, String> collect = HOSTING.entrySet().stream() .filter(map -> map.getKey() == 2) .collect(Collectors.toMap(p -> p.getKey(), p -> p.getValue()));  System.out.println(collect); //output : {2=heroku.com}  } }