01 引入jar
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-collections4</artifactId>
<version>4.4</version>
</dependency>
02 CollectionUtils
2.1 集合判空操作
List<Integer> emptyList = new ArrayList<Integer>();
List<Integer> nullList = null;
List<Integer> hasValueList = new ArrayList<Integer>();
hasValueList.add(5);
hasValueList.add(6);
//判断集合是否为空 ----- isEmpty 判断数组是否为空(null)
System.out.println(CollectionUtils.isEmpty(emptyList)); //true
System.out.println(CollectionUtils.isEmpty(nullList)); //true
System.out.println(CollectionUtils.isEmpty(hasValueList)); //false
//判断集合是否不为空-----isNotEmpty 判断数组不为空
System.out.println(CollectionUtils.isNotEmpty(emptyList)); //false
System.out.println(CollectionUtils.isNotEmpty(nullList)); //false
System.out.println(CollectionUtils.isNotEmpty(hasValueList)); //true
2.2 集合比较操作
isEqualCollection 判断两个集合的值是否相等isSubCollection 判断一个集合是否是另外一个集合的子集
List<Integer> c1 = new ArrayList<Integer>();
c1.add(2);
c1.add(1);
List<Integer> c2 = new ArrayList<Integer>();
c2.add(1);
c2.add(2);
List<Integer> c3 = new ArrayList<Integer>();
c3.add(1);
//比较两集合值
System.out.println(CollectionUtils.isEqualCollection(c1,c2)); //true
System.out.println(CollectionUtils.isEqualCollection(c1,c3)); //false
System.out.println(CollectionUtils.isSubCollection(c3,c1)); // true
System.out.println(CollectionUtils.isSubCollection(c1,c3)); // false
2.3 集合运算
subtract 两个集合的差集intersection 两个集合的交集disjunction 交集的补集union 两个集合的并集
List<Integer> op1 = new ArrayList<Integer>();
op1.add(1);
op1.add(2);
op1.add(3);;
List<Integer> op2 = new ArrayList<Integer>();
op2.add(3);
op2.add(3);
op2.add(4);
op2.add(5);
//并集
System.out.println(CollectionUtils.union(op1, op2)); //[1, 2, 3, 3, 4, 5]
//交集
System.out.println(CollectionUtils.intersection(op1, op2)); //[3]
//交集的补集
System.out.println(CollectionUtils.disjunction(op1, op2)); //[1, 2, 3, 4, 5]
//差集
System.out.println(CollectionUtils.subtract(op1, op2)); //[1, 2]
System.out.println(CollectionUtils.subtract(op1, op2)); //[3, 4, 5]
2.4 数组倒序
// reverseArray 将数组元素倒序
Integer[] list = new Integer[]{1,2,3,4,5};
CollectionUtils.reverseArray(list);
for (int i : list){
System.out.println(i);
}
03 MapUtils
3.1 将特定的数组放入map中
Map colorMap = MapUtils.putAll(new HashMap(), new String[][] {
{"RED", "#FF0000"},
{"GREEN", "#00FF00"},
{"BLUE", "#0000FF"}
});
Map colorMap1 = MapUtils.putAll(new HashMap(), new String[] {
"RED", "#FF0000",
"GREEN", "#00FF00",
"BLUE", "#0000FF"
});
Map colorMap3 = MapUtils.putAll(new HashMap(), new Map.Entry[] {
new DefaultMapEntry("RED", "#FF0000"),
new DefaultMapEntry("GREEN", "#00FF00"),
new DefaultMapEntry("BLUE", "#0000FF")
});
3.2 map的判空操作
Map<String, String> nullMap = null;
Map<String, String> emptyMap = new HashMap<>();
Map<String, String> hasValueMap = new HashMap<>();
hasValueMap.put("1","1");
// 判断map为空(empty,null)
System.out.println(MapUtils.isEmpty(nullMap)); //true
System.out.println(MapUtils.isEmpty(emptyMap)); //true
System.out.println(MapUtils.isEmpty(hasValueMap)); //false
// 判断map不为空
System.out.println(MapUtils.isNotEmpty(nullMap)); //false
System.out.println(MapUtils.isNotEmpty(emptyMap)); //false
System.out.println(MapUtils.isNotEmpty(hasValueMap)); //true
04 参考文档
官方文档：http://commons.apache.org/proper/commons-collections/userguide.html
