使用反射对bean的collection属性赋值

Posted 2020-12-04

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