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
标签：制造者,function,predicate,code,Java,after,util,return,Lambda From： https://www.cnblogs.com/LarryBlogger/p/16916848.html