使用null原因在异常上设置原因时"无法覆盖原因"

Question

我有一个RuntimeException没有原因(t.getCause() returns null).当我的代码运行时t.initCause(exceptionToAttach),它会给我一条IllegalStateException消息"无法覆盖原因".

我不会想到这是可能的.exceptionToAttach只是一个新的RuntimeException(),它似乎因某种原因而被设置为原因.

有什么想法发生了什么？

编辑一些相关的代码

public static void addCause(Throwable e, Throwable exceptionToAttach) {
    // eff it, java won't let me do this right - causes will appear backwards sometimes (ie the rethrow will look like it came before the cause) 
    Throwable c = e;
    while(true) {
        if(c.getCause() == null) {
            break;
        }
        //else
        c = c.getCause();        // get cause here will most likely return null : ( - which means I can't do what I wanted to do
    }

    c.initCause(exceptionToAttach);
}

Answer 1

负责该IllegalStateException异常的代码是:

public class Throwable implements Serializable {
    private Throwable cause = this;        
    public synchronized Throwable initCause(Throwable cause) {
        if (this.cause != this)
            throw new IllegalStateException("Can't overwrite cause");
        if (cause == this)
            throw new IllegalArgumentException("Self-causation not permitted");
        this.cause = cause;
        return this;
    }
// ..
}

这意味着你不能调用构造函数public Throwable(String message, Throwable cause)然后在同一个实例上调用initCause.

我认为您的代码已经调用public Throwable(String message, Throwable cause),null作为传递cause,然后尝试调用initCause不允许的内容.