我如何捕获ClassCastException？

Question

我正在尝试从xml反序列化对象时捕获ClassCastException.

所以,

try {
    restoredItem = (T) decoder.readObject();
} catch (ClassCastException e){
    //don't need to crash at this point,
   //just let the user know that a wrong file has been passed.
}

然而,这不会因为异常没有被抓住.你会建议什么？

Answer 1

问题中的代码应该为您提供未经检查的强制警告.听听-Xlint.

所有编译器都知道T是它的边界,它可能没有(除了显式扩展Object和null类型的超级).因此,运行时的强制转换是(对象) - 不是很有用.

你可以做的是传入参数化类型的类的实例(假设它不是通用的).

class MyReader<T> {
    private final Class<T> clazz;
    MyReader(Class<T> clazz) {
        if (clazz == null) {
            throw new NullPointerException();
        }
        this.clazz = clazz;
    }
    public T restore(String from) {
        ...
        try {
            restoredItem = clazz.cast(decoder.readObject());
            ...
            return restoredItem;
        } catch (ClassCastException exc) {
            ...
        }
    }
}

或者作为通用方法:

    public <T> T restore(Class<T> clazz, String from) {
        ...
        try {
            restoredItem = clazz.cast(decoder.readObject());
            ...