反射对bean的collection属性赋值
对collection使用反射创建时会遇到不知道具体实现类型而烦恼
比如：
class School{ private List classes ; //班级列表 public void setClasses(List classes){ this.classes=classes; } pulbic List getClasses(){ return this classes; } }Class<?> schoolClazz=Class.forName(School.class.getTypeName());schoolClazz.getMethod("setClasses",argsClass);//这里argsClass应该是具体的实现类 很明确这里是需要Arraylist 但是如果是这样代码 class School{ private Collection classes ; //班级列表 public void setClasses(Collection classes){ this.classes=classes; } pulbic Collection getClasses(){ return this classes; } }//惨了 不知道实现类是什么了 应该是ArrayList.class 还是 HashSet.class ?没办法了？参考下spring里面的代码：public static <E> Collection<E> createCollection(Class<?> collectionType, @Nullable Class<?> elementType, int capacity) { Assert.notNull(collectionType, "Collection type must not be null"); if (collectionType.isInterface()) { if (Set.class == collectionType || Collection.class == collectionType) { return new LinkedHashSet<>(capacity); } else if (List.class == collectionType) { return new ArrayList<>(capacity); } else if (SortedSet.class == collectionType || NavigableSet.class == collectionType) { return new TreeSet<>(); } else { throw new IllegalArgumentException("Unsupported Collection interface: " + collectionType.getName()); } } else if (EnumSet.class == collectionType) { Assert.notNull(elementType, "Cannot create EnumSet for unknown element type"); // Cast is necessary for compilation in Eclipse 4.4.1. return (Collection<E>) EnumSet.noneOf(asEnumType(elementType)); } else { if (!Collection.class.isAssignableFrom(collectionType)) { throw new IllegalArgumentException("Unsupported Collection type: " + collectionType.getName()); } try { return (Collection<E>) ReflectionUtils.accessibleConstructor(collectionType).newInstance(); } catch (Throwable ex) { throw new IllegalArgumentException( "Could not instantiate Collection type: " + collectionType.getName(), ex); } }}这里返回了具体的实现类 直接使用它的返回的具体实现类