Java 用Lambda实现一个通用的制造者工具
在我们日常开发中，虽然是用了lombok在实体类中已经帮我们省了get、set方法，但是在公司的项目中，还是经常会出现new一个对象然后一个个的给它set值的情况，太丑了，如下图
List<String> staffList = Arrays.asList(distribute.getStaffIds().split(","));
for(String staffId : staffList) {
EbCorporateActivityDistributeStaffList distributeStaffList = new EbCorporateActivityDistributeStaffList();
distributeStaffList.setDistributeId(distribute.getId());
distributeStaffList.setStaffId(staffId);
distributeStaffListMapper.insert(distributeStaffList);
}
后来我专门的去网上学习、研究，如何避免这个问题，最后封装了一个工具类，如下
我处于两种原因喜欢这种建造方式 1、提到的setter方法去建造对象，可能需要new先创建出来，然后用一行行代码setXX去完成属性的初始化，我个人是不太喜欢这样的编码风格 2、这个建造者最想表达的是"惰性思想"，只有在最后build之后才会拿到构造好的（属性初始化完成的）对象实例，这在高并发环境下是相对安全的， 否则在set过程中，对象实例随时可以被获取的，就会导致没有初始化完成的对象实例提前暴露， 当然你也可以通过别的方式去避免这样的问题，我的这个想法只是其中一种解法 我写的有问题的地方或者你们有更好的方法，欢迎评论，大家互相学习
先来了解一下这些函数式接口
JDK提供了大量常用的函数式接口以丰富Lambda的典型使用场景，它们主要在java.util.function 包中被提供。
Supplier接口
java.util.function.Supplier<T> 接口仅包含一个无参的方法： T get() 。用来获取一个泛型参数指定类型的对象数据。由于这是一个函数式接口，这也就意味着对应的Lambda表达式需要“对外提供”一个符合泛型类型的对象数据。
package java.util.function; /** * Represents a supplier of results. * * <p>There is no requirement that a new or distinct result be returned each * time the supplier is invoked. * * <p>This is a <a href="package-summary.html">functional interface</a> * whose functional method is {@link #get()}. * * @param <T> the type of results supplied by this supplier * * @since 1.8 */ @FunctionalInterface public interface Supplier<T> { /** * Gets a result. * * @return a result */ T get(); }
Consumer接口
java.util.function.Consumer<T> 接口则正好与Supplier接口相反，它不是生产一个数据，而是消费一个数据，其数据类型由泛型决定。
package java.util.function; import java.util.Objects; /** * Represents an operation that accepts a single input argument and returns no * result. Unlike most other functional interfaces, {@code Consumer} is expected * to operate via side-effects. * * <p>This is a <a href="package-summary.html">functional interface</a> * whose functional method is {@link #accept(Object)}. * * @param <T> the type of the input to the operation * * @since 1.8 */ @FunctionalInterface public interface Consumer<T> { /** * Performs this operation on the given argument. * * @param t the input argument */ void accept(T t); /** * Returns a composed {@code Consumer} that performs, in sequence, this * operation followed by the {@code after} operation. If performing either * operation throws an exception, it is relayed to the caller of the * composed operation. If performing this operation throws an exception, * the {@code after} operation will not be performed. * * @param after the operation to perform after this operation * @return a composed {@code Consumer} that performs in sequence this * operation followed by the {@code after} operation * @throws NullPointerException if {@code after} is null */ default Consumer<T> andThen(Consumer<? super T> after) { Objects.requireNonNull(after); return (T t) -> { accept(t); after.accept(t); }; } }
Predicate接口
有时候我们需要对某种类型的数据进行判断，从而得到一个boolean值结果。这时可以使用java.util.function.Predicate<T> 接口。
package java.util.function; import java.util.Objects; /** * Represents a predicate (boolean-valued function) of one argument. * * <p>This is a <a href="package-summary.html">functional interface</a> * whose functional method is {@link #test(Object)}. * * @param <T> the type of the input to the predicate * * @since 1.8 */ @FunctionalInterface public interface Predicate<T> { /** * Evaluates this predicate on the given argument. * * @param t the input argument * @return {@code true} if the input argument matches the predicate, * otherwise {@code false} */ boolean test(T t); /** * Returns a composed predicate that represents a short-circuiting logical * AND of this predicate and another. When evaluating the composed * predicate, if this predicate is {@code false}, then the {@code other} * predicate is not evaluated. * * <p>Any exceptions thrown during evaluation of either predicate are relayed * to the caller; if evaluation of this predicate throws an exception, the * {@code other} predicate will not be evaluated. * * @param other a predicate that will be logically-ANDed with this * predicate * @return a composed predicate that represents the short-circuiting logical * AND of this predicate and the {@code other} predicate * @throws NullPointerException if other is null */ default Predicate<T> and(Predicate<? super T> other) { Objects.requireNonNull(other); return (t) -> test(t) && other.test(t); } /** * Returns a predicate that represents the logical negation of this * predicate. * * @return a predicate that represents the logical negation of this * predicate */ default Predicate<T> negate() { return (t) -> !test(t); } /** * Returns a composed predicate that represents a short-circuiting logical * OR of this predicate and another. When evaluating the composed * predicate, if this predicate is {@code true}, then the {@code other} * predicate is not evaluated. * * <p>Any exceptions thrown during evaluation of either predicate are relayed * to the caller; if evaluation of this predicate throws an exception, the * {@code other} predicate will not be evaluated. * * @param other a predicate that will be logically-ORed with this * predicate * @return a composed predicate that represents the short-circuiting logical * OR of this predicate and the {@code other} predicate * @throws NullPointerException if other is null */ default Predicate<T> or(Predicate<? super T> other) { Objects.requireNonNull(other); return (t) -> test(t) || other.test(t); } /** * Returns a predicate that tests if two arguments are equal according * to {@link Objects#equals(Object, Object)}. * * @param <T> the type of arguments to the predicate * @param targetRef the object reference with which to compare for equality, * which may be {@code null} * @return a predicate that tests if two arguments are equal according * to {@link Objects#equals(Object, Object)} */ static <T> Predicate<T> isEqual(Object targetRef) { return (null == targetRef) ? Objects::isNull : object -> targetRef.equals(object); } }
Function接口
java.util.function.Function<T,R> 接口用来根据一个类型的数据得到另一个类型的数据，前者称为前置条件，后者称为后置条件。
package java.util.function; import java.util.Objects; /** * Represents a function that accepts one argument and produces a result. * * <p>This is a <a href="package-summary.html">functional interface</a> * whose functional method is {@link #apply(Object)}. * * @param <T> the type of the input to the function * @param <R> the type of the result of the function * * @since 1.8 */ @FunctionalInterface public interface Function<T, R> { /** * Applies this function to the given argument. * * @param t the function argument * @return the function result */ R apply(T t); /** * Returns a composed function that first applies the {@code before} * function to its input, and then applies this function to the result. * If evaluation of either function throws an exception, it is relayed to * the caller of the composed function. * * @param <V> the type of input to the {@code before} function, and to the * composed function * @param before the function to apply before this function is applied * @return a composed function that first applies the {@code before} * function and then applies this function * @throws NullPointerException if before is null * * @see #andThen(Function) */ default <V> Function<V, R> compose(Function<? super V, ? extends T> before) { Objects.requireNonNull(before); return (V v) -> apply(before.apply(v)); } /** * Returns a composed function that first applies this function to * its input, and then applies the {@code after} function to the result. * If evaluation of either function throws an exception, it is relayed to * the caller of the composed function. * * @param <V> the type of output of the {@code after} function, and of the * composed function * @param after the function to apply after this function is applied * @return a composed function that first applies this function and then * applies the {@code after} function * @throws NullPointerException if after is null * * @see #compose(Function) */ default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) { Objects.requireNonNull(after); return (T t) -> after.apply(apply(t)); } /** * Returns a function that always returns its input argument. * * @param <T> the type of the input and output objects to the function * @return a function that always returns its input argument */ static <T> Function<T, T> identity() { return t -> t; } }
学完了这些后，我做了个通用的建造者工具类，代码如下
package com.tring.ysyn.util; import java.util.ArrayList; import java.util.List; import java.util.function.Consumer; import java.util.function.Supplier; /** * @author Tring * date 2022-11-22 */ public class Builder<T> { /** * 存储调用方 指定构造类的 构造器 */ private final Supplier<T> constructor; /** * 存储 指定类 所有需要初始化的属性 */ private final List<Consumer> dInject = new ArrayList<>(); private Builder(Supplier<T> constructor){ this.constructor = constructor; } public static <T> Builder<T> builder(Supplier<T> constructor){ return new Builder<>(constructor); } public <P1> Builder<T> with(Builder.DinjectConsumer<T,P1> consumer,P1 p1){ Consumer<T> c = instance ->consumer.accept(instance,p1); dInject.add(c); return this; } public T build(){ //调用supplier 生成类示例 T instance = constructor.get(); //调用传入的setter方法，完成属性的初始化 dInject.forEach(dInject -> dInject.accept(instance)); //返回构造完成的类实例 return instance; } @FunctionalInterface public interface DinjectConsumer<T,P1>{ void accept(T t,P1 p1); } }
测试类
package com.tring.ysyn.util; import com.tring.ysyn.entity.SysUser; /** * @author Tring * date 2022-11-22 */ public class Test { public static void main(String[] args) { //测试 SysUser user = Builder.builder(SysUser::new).with(SysUser::setNickName,"张三").with(SysUser::setPhone,"13222222222").build(); System.out.println(user); } }
效果图
