@Getter
@Setter
@AllArgsConstructor
@ToString
public class UserInfo {
private long id;
private String name;
private int age;
private Date birthday;
private String sex;
}
private static SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
private static List<UserInfo> userInfos;
static {
UserInfo userInfo = new UserInfo(1, "test1", 10, new Date(System.currentTimeMillis() / 2), "男");
UserInfo userInfo11 = new UserInfo(2, "test2", 110, new Date(System.currentTimeMillis() / 3), "女");
UserInfo userInfo12 = new UserInfo(3, "test3", 15, new Date(System.currentTimeMillis() / 2), "男");
UserInfo userInfo13 = new UserInfo(4, "test4", 16, new Date(System.currentTimeMillis() / 4), "女");
UserInfo userInfo14 = new UserInfo(5, "test5", 17, new Date(System.currentTimeMillis() / 5), "男");
UserInfo userInfo15 = new UserInfo(6, "test6", 33, new Date(System.currentTimeMillis() / 2), "女");
UserInfo userInfo16 = new UserInfo(7, "test7", 40, new Date(System.currentTimeMillis() / 4), "男");
UserInfo userInfo17 = new UserInfo(8, "test8", 56, new Date(System.currentTimeMillis() / 6), "女");
UserInfo userInfo18 = new UserInfo(9, "test9", 78, new Date(System.currentTimeMillis() / 7), "男");
UserInfo userInfo19 = new UserInfo(10, "test10", 25, new Date(System.currentTimeMillis() / 6), "女");
UserInfo userInfo1 = new UserInfo(11, "test11", 87, new Date(System.currentTimeMillis() / 3), "男");
userInfos = Lists.newArrayList(userInfo, userInfo1, userInfo11, userInfo12, userInfo13, userInfo14, userInfo15, userInfo16, userInfo17, userInfo18, userInfo19);
}
select * from userinfo
@org.junit.Test
public void test() {
List<UserInfo> collect = userInfos.stream().collect(Collectors.toList());
collect.forEach(System.out::println);
}
select id from userinfo
@org.junit.Test
public void test2() {
List<Long> collect = userInfos.stream().map(UserInfo::getId).collect(Collectors.toList());
collect.forEach(System.out::println);
}
select * from userinfo where age>10
@org.junit.Test
public void test4() {
List<UserInfo> collect = userInfos.stream().filter(i -> i.getAge() > 10).collect(Collectors.toList());
collect.forEach(System.out::println);
}
select age,name,birthday from userinfo where age>10
@org.junit.Test
public void test4() {
List<UserInfo> collect = userInfos.stream().filter(i -> i.getAge() > 10).map(m -> {
UserInfo userInfo = new UserInfo();
userInfo.setAge(m.getAge());
userInfo.setName(m.getName());
userInfo.setBirthday(m.getBirthday());
return userInfo;
}).collect(Collectors.toList());
collect.forEach(System.out::println);
}
select distinct sex from userinfo where age>10
@org.junit.Test
public void test5() {
List<String> collect = userInfos.stream()
.filter(i -> i.getAge() > 10).map(UserInfo::getSex)
.distinct().collect(Collectors.toList());
collect.forEach(System.out::println);
}
select * from userinfo GROUP BY sex
@org.junit.Test
public void test6() {
Map<String, List<UserInfo>> collect = userInfos.stream().collect(Collectors.groupingBy(UserInfo::getSex));
collect.forEach((k,v)->{
System.out.println("========================================================");
v.forEach(i-> System.out.println("分组的字段："+k+",对应的数据："+i.toString()));
});
}
select * from userinfo order by age
@org.junit.Test
public void test7() {
List<UserInfo> collect = userInfos.stream().sorted(Comparator.comparing(UserInfo::getAge))
.collect(Collectors.toList());
collect.forEach(System.out::println);
}
select * from userinfo order by age desc
@org.junit.Test
public void test7() {
List<UserInfo> collect = userInfos.stream().sorted(Comparator.comparing(UserInfo::getAge).reversed())
.collect(Collectors.toList());
collect.forEach(System.out::println);
}
select max(age) from userinfo
@org.junit.Test
public void test8() {
OptionalInt max= userInfos.stream().mapToInt(UserInfo::getAge).max();
System.out.println(max.getAsInt());
}
select min(age) from userinfo
@org.junit.Test
public void test8() {
OptionalInt min= userInfos.stream().mapToInt(UserInfo::getAge).min();
System.out.println(min.getAsInt());
}
select sum(age) from userinfo
@org.junit.Test
public void test10() {
int sum = userInfos.stream().mapToInt(UserInfo::getAge).sum();
System.out.println(sum);
}
select count(*) from userinfo
@org.junit.Test
public void test11() {
long count = userInfos.stream().count();
System.out.println(count);
}
select avg(age) from userinfo
@org.junit.Test
public void test13() {
OptionalDouble average = userInfos.stream().mapToDouble(UserInfo::getAge).average();
System.out.println(average.getAsDouble());
}
select * from userinfo limit 3,5
skip：从头开始跳过多少条数据
limit：限制显示多少条数据
两个api组合可以做分页功能
@org.junit.Test
public void test12() {
List<UserInfo> collect = userInfos.stream().skip(3).limit(5).collect(Collectors.toList());
collect.forEach(System.out::println);
}
其他实用的例子：
anyMatch、allMatch、noneMatch都是返回boolean值
@org.junit.Test
public void test14() {
//检查集合中对象的name是否存在test1的
System.out.println(userInfos.stream().anyMatch(s->StringUtils.equals(s.getName(),"test1")));
//检查集合中对象的name是否全是test1
System.out.println(userInfos.stream().allMatch(s->StringUtils.equals(s.getName(),"test1")));
//检查集合中对象的name是否全不存在test1
System.out.println(userInfos.stream().noneMatch(s-> StringUtils.equals(s.getName(),"test1")));
}
partitioningBy：可以按照某种条件进行分区
@org.junit.Test
public void test15() {
Map<Boolean, List<UserInfo>> collect = userInfos.stream().collect(Collectors.partitioningBy(i -> i.getAge() > 70));
collect.forEach((k,v)->{
System.out.println("========================================================");
v.forEach(i-> System.out.println("age是否大于70岁："+k+",对应的数据："+i.toString()));
});
}
reduce:累计数，这个和sum的区别就是它可以定义初始值
@org.junit.Test
public void test16() {
int sum = userInfos.stream().mapToInt(UserInfo::getAge).sum();
System.out.println("sum:"+sum);
//假设初始值10的位置是f
//b是遍历集合出入的值
//a是每次都作为累计的结果复制到初始化值f的位置（也就是下面等于10的位置）
//每次遍历就相当于做b+f的操作
int reduce = userInfos.stream().mapToInt(UserInfo::getAge).reduce(10,(a,b)->{
a+=b;
return a;
});
System.out.println("reduce:"+reduce);
}
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