总结之Function、Consumer等接口使用

た入场券 2022-08-29 04:28 192阅读 0赞

## 使用一： ##

java可以通过Function、Consumer等接口的lambda表单式形式，提提取公共方法，把变化的部分的代码 放入lambda中，如下：  
xxxxxx  
aaaaaa  
xxxxxx

xxxxxx  
bbbbbb  
xxxxxx

代码提取

public Result<User> loadRecords(Function<BpmInst,Boolean> function,List<Product>> query) {
           xxxx
    	getxx（function.apply(xxx））
           xxxx
        }
    
    loadRecords((BpmInst bpmInst) -> bpmInst.getAppId() == "D001"),query);

## 使用二： ##

还可以用来提取方法筛选条件，把条件提取到方法使用的时候使用，通过匿名内部类的形式传入，Function等方法lambda实现匿名内部类，如下：

/**
        * @Param [bpmInstList, filterBpmInst]
        * @return java.util.List<com.redxun.bpm.core.entity.BpmInst>
        * @Description 筛选方法，把筛选条件提取成对象，筛选不在循环里实现，可以同时接口实现类，或者匿名内部类实现
        * @author liuzonghua
        * @date 2021/7/20 9:18
        **/
        public static List<BpmInst> filterBpmInstData(List<BpmInst> bpmInstList,FilterBpmInst filterBpmInst){
            List<BpmInst> bpmInsts = new ArrayList<>();
            for(BpmInst bpmInst:bpmInstList){
                if(filterBpmInst.Test(bpmInst)){
                    bpmInsts.add(bpmInst);
                }
            }
            return bpmInsts;
        }
    
        public static List<BpmInst> filterBpmInstData2(List<BpmInst> bpmInstList, Function<BpmInst,Boolean> function){
            List<BpmInst> bpmInsts = new ArrayList<>();
            for(BpmInst bpmInst:bpmInstList){
                if(function.apply(bpmInst)){
                    bpmInsts.add(bpmInst);
                }
            }
            return bpmInsts;
        }
    
        /**
        * @Param
        * @return 
        * @Description 筛选接口
        * @author liuzonghua
        * @date 2021/7/20 9:20
        **/
        @FunctionalInterface
        public interface FilterBpmInst{
            boolean Test(BpmInst bpmInst);
    
        }
    
    
    System.out.println(JSON.toJSONString(filterBpmInstData(nodeConfigList, new FilterBpmInst() {
                @Override
                public boolean Test(BpmInst bpmInst) {
                    if("G001".equals(bpmInst.getAppId())){
                        return true;
                    }
                    return false;
                }
            }),true));
            //lambda表达式
            System.out.println(JSON.toJSONString(filterBpmInstData(nodeConfigList,(BpmInst bpmInst) -> bpmInst.getAppId() == "G001")));
    
            System.out.println(JSON.toJSONString(filterBpmInstData2(nodeConfigList,(BpmInst bpmInst) -> bpmInst.getAppId() == "D001")));

## 补充function等类的，andThen，compose方法，链式处理 ##

接口内部实现如下：

/**
         * 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));
        }

例子：

Function<Integer,Integer> functionA = i->(i+1);
     Function<Integer,Integer> functionB = i->(i*3);

可以看出来，a执行后b执行

System.out.println(functionA.andThen(functionB).apply(2));

同

System.out.println(functionB.apply(functionA.apply(2)));

b执行后a执行

System.out.println(functionA.compose(functionB).apply(2));

同

System.out.println(functionA.apply(functionB.apply(2)));