番石榴谓词未能过滤收集

Question

我有以下方法使用Predicate过滤集合,抛出propertyName不在给定的允许值列表中的任何成员.它使用Common-BeanUtils从对象中提取值,该值必须是String:

public static <T> void filterListByStringPropertyWithAllowableValues(List<T> listToFilter, 
        final String propertyName, 
        final List<String> allowedValues) {

    Predicate<T> allowedValuesPredicate = new Predicate<T>() {

        @Override
        public boolean apply(T arg0) {

            String value;
            boolean result = false;
            try {
                value = BeanUtils.getProperty(arg0, propertyName);
                System.out.println(value);
                result = allowedValues.contains(value);
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            } 

            return result;


        }
    };

    Iterables.filter(listToFilter, allowedValuesPredicate);

}

不幸的是,我的测试彻底失败了.

@Test
public void testfilterListByStringPropertyWithAllowableValues() throws Exception {

    TestClass item1 = new TestClass("value1","whatever1");
    TestClass item2 = new TestClass("value2","whatever2");
    TestClass item3 = new TestClass("value3","whatever3");

    List<TestClass> initialList = Lists.newArrayList(item1, item2, item3);

    MyCollectionUtils.filterListByStringPropertyWithAllowableValues(initialList, "importantField", 
            Lists.newArrayList("value1","value2"), 3);

    assertTrue("Collection size should be 2. Actual: " + initialList.size(), initialList.size() == 2);
}

我在这里犯了一个令人难以置信的愚蠢错误吗？

更新:工作代码如下.

public static <T> List<T> filterListByStringPropertyWithAllowableValues(List<T> listToFilter, 
        final String propertyName, 
        final Set<String> allowedValues) {

    Predicate<T> allowedValuesPredicate = new Predicate<T>() {

        @Override
        public boolean apply(T arg0) {

            String value;
            boolean result = false;
            try {
                value = BeanUtils.getProperty(arg0, propertyName);
                System.out.println(value);
                result = allowedValues.contains(value);
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            } 

            return result;

        }
    };

    return Lists.newArrayList(Iterables.filter(listToFilter, allowedValuesPredicate));

}

Answer 1

是的,你做了一个令人难以置信的愚蠢的错误;-)

您没有返回已过滤的列表.filter()不会修改给定的列表.它返回一个过滤的Iterable.

另外,allowedValues应该是HashSet而不是List.这将使您的过滤器更有效.HashSet.contains()运行在固定的时间,而List.contains()为O(n).