Google Guava 实战之Maps篇
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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boolean
boolean 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>() {
@Override
public 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>() {
@Override
public 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
@Override
public 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
@Override
public 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uppe
Range<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
@Override
public 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}
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