1 filter方法

按照指定条件过滤数据，保留原始数据类型。

2 Usage

2.1 基础类型数据过滤

过滤字符串为例：构造List<String>

 /*** 1.1过滤数据：构造字符串列表.List<A>->List<A>*/@Testpublic void filterStringWithSpecificCondition() {List<String> list = Stream.of("female", "male", "female", "male").collect(Collectors.toList());logger.info(">>>>>>>>>>原始数据：\n{}", list);List<String> listAfterFilter = list.stream().filter(s -> null != s && !"male".equals(s)).collect(Collectors.toList());logger.info(">>>>>>>>>>过滤后的数据：\n{}", listAfterFilter);}

在这里插入图片描述

2.2 对象过滤

过滤对象中满足条件的数据，返回对象

测试样例

/*** 1.2过滤数据：构造实体列表.List<A>->List<A>*/@Testpublic void  filterEntityWithSpecificCondition() {List<UserEntity> userEntityList = new ArrayList<>();userEntityList.add(new UserEntity("1", "111", "male"));userEntityList.add(new UserEntity("2", "222", "female"));userEntityList.add(new UserEntity("3", "333", "male"));userEntityList.add(new UserEntity("4", "444", "female"));logger.info(">>>>>>>>>>原始数据：\n{}", userEntityList);List<UserEntity> listAfterFilter = userEntityList.stream().filter(s -> null != s && !"male".equals(s.getSex())).collect(Collectors.toList());logger.info(">>>>>>>>>>过滤后的数据：\n" + listAfterFilter);}

测试结果
引用传递
过滤后的数据为仍为原始的对象，因此，修改过滤后的数据，原始数据同时会变化，如果原始数据有其他用途，则需要在过滤时新建对象，保证值传递。
值传递

    /*** 1.3过滤数据：构造实体列表，创建新对象.List<A>->List<A>*/@Testpublic void  filterEntityWithSpecificConditionAndCreateNewObject() {List<UserEntity> userEntityList = new ArrayList<>();userEntityList.add(new UserEntity("1", "111", "male"));userEntityList.add(new UserEntity("2", "222", "female"));userEntityList.add(new UserEntity("3", "333", "male"));userEntityList.add(new UserEntity("4", "444", "female"));logger.info(">>>>>>>>>>原始数据：\n{}", userEntityList);List<UserEntity> listAfterFilter = userEntityList.stream().filter(s -> null != s && !"male".equals(s.getSex())).map(UserEntity::copy).collect(Collectors.toList());logger.info(">>>>>>>>>>过滤后的数据：\n" + listAfterFilter);}

UserEntity

package com.monkey.java_study.common.entity;/*** User实体** @author xindaqi* @since 2021-01-23*/public class UserEntity {/*** 用户id*/private String uid;/*** 用户名称*/private String nickname;/*** 用户性别*/private String sex = "haha";public UserEntity() {}public UserEntity(String uid) {this.uid = uid;}public UserEntity(String uid, String nickname, String sex) {this.uid = uid;this.nickname = nickname;this.sex = sex;}public UserEntity copy() {return new UserEntity(uid, nickname, sex);}public String getUid() {return uid;}public void setUid(String uid) {this.uid = uid;}public String getNickname() {return nickname;}public void setNickname(String nickname) {this.nickname = nickname;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}@Overridepublic String toString() {return "UserEntity{" +"uid=" + uid +", nickname='" + nickname + '\'' +", sex='" + sex + '\'' +'}';}
}

在这里插入图片描述

3 完整样例

package com.monkey.java_study.functiontest;import com.monkey.java_study.common.entity.UserEntity;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;/*** Stream测试.** @author xindaqi* @date 2021-10-15 10:06*/
public class StreamTest {private static final Logger logger = LoggerFactory.getLogger(StreamTest.class);/*** 1.1过滤数据：构造字符串列表.List<A>->List<A>*/@Testpublic void filterStringWithSpecificCondition() {List<String> list = Stream.of("female", "male", "female", "male").collect(Collectors.toList());logger.info(">>>>>>>>>>原始数据：\n{}", list);List<String> listAfterFilter = list.stream().filter(s -> null != s && !"male".equals(s)).collect(Collectors.toList());logger.info(">>>>>>>>>>过滤后的数据：\n{}", listAfterFilter);}/*** 1.2过滤数据：构造实体列表.List<A>->List<A>*/@Testpublic void  filterEntityWithSpecificCondition() {List<UserEntity> userEntityList = new ArrayList<>();userEntityList.add(new UserEntity("1", "111", "male"));userEntityList.add(new UserEntity("2", "222", "female"));userEntityList.add(new UserEntity("3", "333", "male"));userEntityList.add(new UserEntity("4", "444", "female"));logger.info(">>>>>>>>>>原始数据：\n{}", userEntityList);List<UserEntity> listAfterFilter = userEntityList.stream().filter(s -> null != s && !"male".equals(s.getSex())).collect(Collectors.toList());logger.info(">>>>>>>>>>过滤后的数据：\n" + listAfterFilter);}/*** 1.3过滤数据：构造实体列表，创建新对象.List<A>->List<A>*/@Testpublic void  filterEntityWithSpecificConditionAndCreateNewObject() {List<UserEntity> userEntityList = new ArrayList<>();userEntityList.add(new UserEntity("1", "111", "male"));userEntityList.add(new UserEntity("2", "222", "female"));userEntityList.add(new UserEntity("3", "333", "male"));userEntityList.add(new UserEntity("4", "444", "female"));logger.info(">>>>>>>>>>原始数据：\n{}", userEntityList);List<UserEntity> listAfterFilter = userEntityList.stream().filter(s -> null != s && !"male".equals(s.getSex())).map(UserEntity::copy).collect(Collectors.toList());logger.info(">>>>>>>>>>过滤后的数据：\n" + listAfterFilter);}
}