WebFlux基础之响应式编程

　　上篇文章，我们简单的了解了WebFlux的一些基础与背景，并通过示例来写了一个demo。我们知道WebFlux是响应式的web框架，其特点之一就是可以通过函数式编程方式配置route。另外究竟什么是响应式编程呢？这篇文章我们就简单探讨一下

一、Java8中的函数式编程

　　百科中这样定义函数式编程：

　　函数式编程是种编程方式，它将电脑运算视为函数的计算。函数编程语言最重要的基础是λ演算（lambda calculus），而且λ演算的函数可以接受函数当作输入（参数）和输出（返回值)。那么在Java8里怎么样来实现它呢？

示例一

在这里我先自己写一个例子

定义接口：

package com.bdqn.lyrk.basic.java;

/**
 * 函数式接口
 *
 * @author chen.nie
 * @date 2018/7/18
 **/
@FunctionalInterface
public interface OperateNumberFunctions {

    void operate(Integer number);

    default void print() {
        
    }
}

　　　　 

　　在定义的接口上添加@FunctionalInterface表明其是函数式接口，这个注解用于检测函数式接口规范，定义函数式接口时该接口内必须有且只有一个抽象的方法。

定义类：

package com.bdqn.lyrk.basic.java;

import java.util.Optional;
import java.util.function.Predicate;

/**
 * 定义函数式编程类
 */
public class NumberFunctions {

    private Integer number;

    private NumberFunctions() {
    }

    private static NumberFunctions numberFunctions = new NumberFunctions();

    public static NumberFunctions of(Integer number) {
        numberFunctions.number = number;
        return numberFunctions;
    }

    public NumberFunctions add(Integer number) {
        numberFunctions.number += number;
        return numberFunctions;
    }

    public NumberFunctions subtraction(Integer number) {
        numberFunctions.number -= number;
        return numberFunctions;
    }

    public Optional filter(Predicate predicate) {
        if (predicate.test(this.number)) return Optional.of(numberFunctions);
        return Optional.ofNullable(new NumberFunctions());

    }

    public void operate(OperateNumberFunctions functions) {
        functions.operate(this.number);
    }
}

 

　　在这里定义类进行简单的运算与过滤条件。那么在Main方法里可以这么写：

package com.bdqn.lyrk.basic.java;

public class Main {

    public static void main(String[] args) {
        NumberFunctions.of(10).add(30).subtraction(2).filter(number -> number>20).get().operate(System.out::println);
    }
}

　　那么输出结果为38

示例二

　　在Java8里有一个类叫Stream。Stream是数据流的意思，这个类略微有点像Reactor中Flux，它提供了类似于操作符的功能，我们来看一个例子：

Main方法

package com.bdqn.lyrk.basic.java;

import java.util.stream.Stream;

import static java.util.stream.Collectors.toList;

public class Main {

    public static void main(String[] args) {
        /*
            在这里先将Stream里的内容做乘2的操作
            然后在进行倒序排序
            紧接着过滤出是4的倍数的数字
            然后转换成集合在打印
         */
        Stream.of(15, 26, 34, 455, 5, 6).map(number -> number * 2).sorted((num1, num2) -> num2 - num1).filter(integer -> integer % 4 == 0).collect(toList()).forEach(System.out::println);
    }
}

　　运行得到的结果：

68
52
12

关于::操作符

　　该操作符是lambda表达式的更特殊写法，使用此操作符可以简化函数式接口的实现，这个方法至少满足以下特定条件：

　　1）方法返回值与函数式接口相同

　　2）方法参数与函数式接口相同

　　举例说明

package java.util.function;

/**
 * Represents a supplier of results.
 *
 * 
There is no requirement that a new or distinct result be returned each
 * time the supplier is invoked.
 *
 * 
This is a functional interface
 * whose functional method is {@link #get()}.
 *
 * @param  the type of results supplied by this supplier
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Supplier {

    /**
     * Gets a result.
     *
     * @return a result
     */
    T get();
}

　　java中Runnable接口:

@FunctionalInterface
public interface Runnable {
    /**
     * When an object implementing interface Runnable is used
     * to create a thread, starting the thread causes the object's
     * run method to be called in that separately executing
     * thread.
     * 

     * The general contract of the method run is that it may
     * take any action whatsoever.
     *
     * @see     java.lang.Thread#run()
     */
    public abstract void run();
}

　　java中的Predicate接口:

package java.util.function;

import java.util.Objects;

/**
 * Represents a predicate (boolean-valued function) of one argument.
 *
 * 
This is a functional interface
 * whose functional method is {@link #test(Object)}.
 *
 * @param  the type of the input to the predicate
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Predicate {

    /**
     * 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.
     *
     * 
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 and(Predicatesuper 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 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.
     *
     * 
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 or(Predicatesuper 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  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  Predicate isEqual(Object targetRef) {
        return (null == targetRef)
                ? Objects::isNull
                : object -> targetRef.equals(object);
    }
}

那么上述的接口分别可以使用如下写法，注意实现该接口的方法特点

package com.bdqn.lyrk.basic.java;

import java.util.function.Predicate;
import java.util.function.Supplier;

public class Main {
    private static int i;

    public static void main(String[] args) {

        /*
            创建对象的方式
         */
        Supplier