Google Guava 实战之Maps篇

 Guava是一种基于开源的Java库,谷歌很多项目使用它的很多核心库。这个库是为了方便编码,并减少编码错误。

 <dependency><groupId>com.google.guava</groupId><artifactId>guava</artifactId><version>27.0.1-jre</version></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId></dependency>

import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.collect.*;
import lombok.AllArgsConstructor;
import lombok.Data;
import org.checkerframework.checker.nullness.qual.Nullable;import java.util.*;/*** author: lucifer* date: 2020/5/26 15:21* description: TODO*/
public class guavaMaps01 {public static void main(String[] args) {Map<String, Object> map1 = new HashMap<>();map1.put("张三", 123);map1.put("李四", 457);map1.put("王五", 235);map1.put("马六", 752);map1.put("王八", 752);Map<String, Object> map2 = new HashMap<>();map2.put("张三", 345);map2.put("马六", 752);map2.put("田七", 125);/*** 1、difference* Maps.difference(Map, Map)用来比较两个Map以获取所有不同点。该方法返回MapDifference对象*/MapDifference<String, Object> difference = Maps.difference(map1, map2);//是否有差异，返回booleanboolean areEqual = difference.areEqual();System.out.println("比较两个Map是否有差异:" + areEqual);//两个map的交集Map<String, Object> entriesInCommon = difference.entriesInCommon();System.out.println("两个map都有的部分（交集）===：" + entriesInCommon);//键相同但是值不同值映射项。返回的Map的值类型为MapDifference.ValueDifference，以表示左右两个不同的值Map<String, MapDifference.ValueDifference<Object>> entriesDiffering = difference.entriesDiffering();System.out.println("键相同但是值不同值映射项===：" + entriesDiffering);//键只存在于左边Map的映射项Map<String, Object> onlyOnLeft = difference.entriesOnlyOnLeft();System.out.println("键只存在于左边Map的映射项:" + onlyOnLeft);//键只存在于右边Map的映射项Map<String, Object> entriesOnlyOnRight = difference.entriesOnlyOnRight();System.out.println("键只存在于右边Map的映射项:" + entriesOnlyOnRight);/*** 2.filterEntries* Maps.filterEntries():过滤map*/Map<String, Object> filterEntries = Maps.filterEntries(map1, input -> {if (input.getValue().equals(123) && Objects.equals(input.getKey(), "张三")) {return true;}return false;});System.out.println("过滤map=====filterEntries:" + filterEntries);/*** 3.filterKeys* Maps.filterKeys():过滤key*/Map<String, Object> filterKeysMap = Maps.filterKeys(map1, new Predicate<String>() {@Overridepublic boolean apply(@Nullable String input) {if (input.equals("李四")) {return true;}return false;}});System.out.println("过滤key=====filterKeys:" + filterKeysMap);/***4.filterValues* Maps.filterValues():过滤value*/Map<String, Object> filterValuesMap = Maps.filterValues(map1, new Predicate<Object>() {@Overridepublic boolean apply(@Nullable Object input) {if (Objects.equals(752, input)) {return true;}return false;}});System.out.println("过滤value=====filterValues:" + filterValuesMap);/*** 5.uniqueIndex* Maps.uniqueIndex():根据属性值找对象* 有一组对象，它们在某个属性上分别有独一无二的值，而我们希望能够按照这个属性值查找对象* 注：Maps.uniqueIndex():必须属性值唯一*否则报错：Exception in thread "main" java.lang.IllegalArgumentException: Multiple entries with same key:xxxxx. To index multiple values under a key, use Multimaps.index.*/List<User> users = new ArrayList<>();users.add(new User("zhangsan", 24));users.add(new User("lisi", 27));users.add(new User("wangwu", 28));//users.add(new User("wangwu",30));ImmutableMap<Object, User> uniqueIndex = Maps.uniqueIndex(users, new Function<User, Object>() {@Nullable@Overridepublic Object apply(@Nullable User user) {return user.getUserName();}});System.out.println("Maps.uniqueIndex()===========uniqueIndex:" + uniqueIndex);/*** 6.index* Multimaps.index(): 根据属性值找对象* 如果您的索引可能将多个值与每个键相关联*/users.add(new User("wangwu", 30));users.add(new User("lisi", 23));ImmutableListMultimap<Object, User> multimap = Multimaps.index(users, new Function<User, Object>() {@Nullable@Overridepublic Object apply(@Nullable User user) {return user.getUserName();}});System.out.println("Multimaps.index()=========multimap:" + multimap);/*** 7.immutableEntry* Maps.immutableEntry():返回不可变的映射条目与指定的键和值*/Map.Entry<String, Integer> immutableEntry = Maps.immutableEntry("李四", 457);System.out.println("Maps.immutableEntry:===============immutableEntry:" + immutableEntry);/*** 8.subMap* Maps.subMap():返回的部分视图， map的键被包含range限制*/TreeMap<Integer, String> TreeMap = Maps.newTreeMap();TreeMap.put(1, "aaa");TreeMap.put(4, "bbb");TreeMap.put(2, "ccc");TreeMap.put(6, "ddd");//返回包含严格大于所有值的范围lower ，比严格小于uppeRange<Integer> range = Range.open(0, 3);NavigableMap<Integer, String> navigableMap = Maps.subMap(TreeMap, range);System.out.println("Maps.subMap()=================navigableMap:" + navigableMap);/*** 9.transformValues* Maps.transformValues:返回一个map，其中每个值都通过函数进行转换。*/Map<String, Object> transformValues = Maps.transformValues(map1, new Function<Object, Object>() {@Nullable@Overridepublic Object apply(@Nullable Object input) {Integer value = Integer.valueOf(input.toString());return value / 2;}});System.out.println("Maps.transformValues===============transformValues:" + transformValues);}
}@AllArgsConstructor
@Data
class User {private String userName;private Integer age;
}

 控制台打印：

比较两个Map是否有差异:false
两个map都有的部分（交集）===：{马六=752}
键相同但是值不同值映射项===：{张三=(123, 345)}
键只存在于左边Map的映射项:{李四=457, 王五=235, 王八=752}
键只存在于右边Map的映射项:{田七=125}
过滤map=====filterEntries:{张三=123}
过滤key=====filterKeys:{李四=457}
过滤value=====filterValues:{马六=752, 王八=752}
Maps.uniqueIndex()===========uniqueIndex:{zhangsan=User(userName=zhangsan, age=24), lisi=User(userName=lisi, age=27), wangwu=User(userName=wangwu, age=28)}
Multimaps.index()=========multimap:{zhangsan=[User(userName=zhangsan, age=24)], lisi=[User(userName=lisi, age=27), User(userName=lisi, age=23)], wangwu=[User(userName=wangwu, age=28), User(userName=wangwu, age=30)]}
Maps.immutableEntry:===============immutableEntry:李四=457
Maps.subMap()=================navigableMap:{1=aaa, 2=ccc}
Maps.transformValues===============transformValues:{李四=228, 张三=61, 马六=376, 王五=117, 王八=376}