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Java8 BiConsumer<T, U> 函数接口浅析分享（含示例，来戳！）

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学起来，开整！Java8 BiConsumer<T, U>函数接口使用分享。

BiConsumer<T, U> 跟我们熟悉的 Consumer< T> 很像，核心思想也是一样的，两者都是表达消费的意思；

源码

BiConsumer<T, U> 提供了两个方法：

• void accept(T t, U u)：传入两个泛型参数（当然方法实现想怎么用自己玩，可以看下面示例场景）；
• BiConsumer<T, U> andThen(BiConsumer<? super T, ? super U> after)：可以理解为在执行 accept 方法前先执行一个前置方法，前置方法执行完成后，会接着执行 accept 方法；

源码

@FunctionalInterface
public interface BiConsumer<T, U> {void accept(T t, U u);default BiConsumer<T, U> andThen(BiConsumer<? super T, ? super U> after) {Objects.requireNonNull(after);return (l, r) -> {accept(l, r);after.accept(l, r);};}
}

accept 方法示例

tips: 需要配合文末示例相关代码类食用

示例一

查询所有学生的成绩：

	@Testpublic void test() {StudentScoreDto studentScoreDto = new StudentScoreDto();Student student = new Student();this.doHandler(student, studentScoreDto, StudentAssemble::queryList, StudentAssemble::calcSort);System.out.println(JSONObject.toJSONString(studentScoreDto));}

执行结果：

示例二

查询 “张三” 同学的成绩：

	@Testpublic void test() {StudentScoreDto studentScoreDto1 = new StudentScoreDto();Student student1 = new Student();student1.setName("张三");this.doHandler(student1, studentScoreDto1, StudentAssemble::queryList, StudentAssemble::calcSort);System.out.println(JSONObject.toJSONString(studentScoreDto1));}

执行结果：

andThen 方法示例

示例一

查询所有学生的成绩，并且输出第一名是哪位同学；

@Testpublic void test() {StudentScoreDto studentScoreDto2 = new StudentScoreDto();Student student2 = new Student();this.doHandler(student2, studentScoreDto2, StudentAssemble::queryList, StudentAssemble::calcSort, StudentAssemble::findFirst);System.out.println(JSONObject.toJSONString(studentScoreDto2));}

执行结果：

示例二

查询所有学生的成绩，并且输出 “李四” 同学的排名和总分；

@Testpublic void test() {StudentScoreDto studentScoreDto3 = new StudentScoreDto();studentScoreDto3.setName("李四");Student student3 = new Student();this.doHandler(student3, studentScoreDto3, StudentAssemble::queryList, StudentAssemble::calcSort, StudentAssemble::findFirst);System.out.println(JSONObject.toJSONString(studentScoreDto3));}

执行结果：

示例相关代码类

tips: 需要配合文末示例相关代码类食用

dohandler 方法

tip：注意这里是方法！！

	public void doHandler(Student student,StudentScoreDto dto,Function<Student, List<StudentScore>> func1,BiConsumer<List<StudentScore>, StudentScoreDto> func2) {List<StudentScore> apply = func1.apply(student);func2.accept(apply, dto);}public void doHandler(Student student,StudentScoreDto dto,Function<Student, List<StudentScore>> func1,BiConsumer<List<StudentScore>, StudentScoreDto> func2,BiConsumer<List<StudentScore>, StudentScoreDto> func3) {List<StudentScore> apply = func1.apply(student);func2.accept(apply, dto);func3.andThen(func2).accept(apply, dto);}

student.java

@AllArgsConstructor
@NoArgsConstructor
@Data
public class Student {/*** 姓名*/private String name;/*** 年龄*/private Integer age;/*** 生日*/@JSONField(format="yyyy-MM-dd HH:mm:ss")private Date birthday;/*** 学号*/private Integer num;@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", age=" + age +", birthday=" + birthday +", num=" + num +'}';}

StudentScore.java

@AllArgsConstructor
@NoArgsConstructor
@Data
public class StudentScore {/*** 名称*/private String name;/*** 科目*/private String subject;/*** 成绩*/private Integer score;}

StudentScoreDto.java

@AllArgsConstructor
@NoArgsConstructor
@Data
public class StudentScoreDto {/*** 名称*/private String name;/*** 科目*/private String subject;/*** 成绩*/private Integer score;/*** 个人排名*/private Integer rank;/*** 全班排名*/private List<StudentScoreDto> rankList;}

StudentAssemble.java

public class StudentAssemble {/*** 查询学生成绩列表** @param student 学生实体对象* @return 学生成绩集合*/public static List<StudentScore> queryList(Student student) {// 模拟查询学生信息List<StudentScore> studentScores = Arrays.asList(new StudentScore("张三", "语文", 81),new StudentScore("张三", "数学", 88),new StudentScore("张三", "英语", 90),new StudentScore("李四", "语文", 72),new StudentScore("李四", "数学", 97),new StudentScore("李四", "英语", 77),new StudentScore("王五", "语文", 95),new StudentScore("王五", "数学", 62),new StudentScore("王五", "英语", 92));if (Objects.isNull(student) || StringUtils.isEmpty(student.getName())) {return studentScores;}String name = student.getName();return studentScores.stream().filter(e -> name.equals(e.getName())).collect(Collectors.toList());}/*** 计算总分以及排名** @param studentScoreList 学生成绩集合* @param studentScoreDto  学生成绩DTO*/public static void calcSort(List<StudentScore> studentScoreList, StudentScoreDto studentScoreDto) {if (studentScoreList == null || studentScoreList.size() == 0) {return;}List<StudentScoreDto> tempList = new ArrayList<>();Map<String, List<StudentScore>> studentScoreMap = studentScoreList.stream().collect(Collectors.groupingBy(StudentScore::getName));for (List<StudentScore> value : studentScoreMap.values()) {if (value == null || value.size() == 0) continue;StudentScore studentScore = value.get(0);// 汇总学生总成绩，如果成绩不存在，则直接给0Integer sumScore = value.stream().map(StudentScore::getScore).reduce(Integer::sum).orElse(0);StudentScoreDto resultDto = new StudentScoreDto();resultDto.setName(studentScore.getName());resultDto.setScore(sumScore);tempList.add(resultDto);}AtomicInteger counter = new AtomicInteger(1);// 处理排名List<StudentScoreDto> resultList = tempList.stream().sorted(Comparator.comparing(StudentScoreDto::getScore).reversed()).collect(Collectors.toList());resultList.forEach(e -> e.setRank(counter.getAndIncrement()));studentScoreDto.setRankList(resultList);}/*** 查询学生成绩** @param studentScoreList 学生成绩集合* @param studentScoreDto  学生成绩DTO*/public static void findFirst(List<StudentScore> studentScoreList, StudentScoreDto studentScoreDto) {if (studentScoreList == null || studentScoreList.size() == 0) {return;}List<StudentScoreDto> rankList = studentScoreDto.getRankList();if (StringUtils.isEmpty(studentScoreDto.getName())) {// 学生名称为空，则输出第一名Optional<StudentScoreDto> first = rankList.stream().min(Comparator.comparing(StudentScoreDto::getRank));if (first.isPresent()) {StudentScoreDto studentScoreDto1 = first.get();System.out.println("第一名是：" + studentScoreDto1.getName() + ", 总分：" + studentScoreDto1.getScore());}return;}// 学生名称不为空，则输出学生排名Optional<StudentScoreDto> first = rankList.stream().filter(e -> studentScoreDto.getName().equals(e.getName())).findFirst();if (first.isPresent()) {StudentScoreDto studentScoreDto1 = first.get();System.out.println(studentScoreDto1.getName() + " 排名：" + studentScoreDto1.getRank() + ", 总分：" + studentScoreDto1.getScore());}}

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