如何在Java中组合Closeable对象？

我正在尝试创建一个管理多个Closeable资源的Java类.C++解决方案可以直接使用大量资源轻松扩展:

class composed_resource
{
    resource_a a;
    resource_b b;
    resource_c c;

    composed_resource(int x)
        : a(x), b(x), c(x)
    { }

    ~composed_resource()
    { }
};

我天真的Java解决方案:

public class ComposedResource implements Closeable
{
    private final ResourceA a;
    private final ResourceB b;
    private final ResourceC c;

    public ComposedResource(int x) /* throws ... */ {
        a = new ResourceA(x);
        try {
            b = new ResourceB(x);
            try {
                c = new ResourceC(x);
            } catch (Throwable t) {
                b.close();
                throw t;
            }
        } catch (Throwable t) {
            a.close();
            throw t;
        }
    }

    @Override
    public void close() throws IOException {
        try {
            a.close();
        } finally {
            try {
                b.close();
            } finally {
                c.close();
            }
        }
    }
}

略有改进的版本:

public class ComposedResource2 implements Closeable
{
    private final ResourceA a;
    private final ResourceB b;
    private final ResourceC c;

    public ComposedResource2(int x) /* throws ... */ {
        try {
            a = new ResourceA(x);
            b = new ResourceB(x);
            c = new ResourceC(x);
        } catch (Throwable t) {
            close();
            throw t;
        }
    }

    @Override
    public void close() throws IOException {
        try {
            if (a != null) a.close();
        } finally {
            try {
                if (b != null) b.close();
            } finally {
                if (c != null) c.close();
            }
        }
    }
}

是否有更优雅的解决方案,避免嵌套的try-catch-blocks,同时仍保持异常安全？它可以通过三种资源进行管理,但更多的是变得笨拙.(如果它是本地范围,我可以使用"try-with-resources"语句,但这不适用于此.)

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我在工作时想到了这一点java.rmi.在构造函数中,我正在创建/查找注册表,查找对象和导出对象.close()需要取消注册和取消导出对象.我想创建包装器对象来处理导出/取消导出(就像我在C++中用来利用RAII),但后来我注意到这对我没什么帮助(我不是那么多Java专家,但我必须用它来上大学).

目前我正在使用ComposedResource2上面的东西,它工作正常.但现在我有兴趣知道是否有更优雅的解决方案.

1> saka1029..：

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像这样使用try-with-resouces.

@Override
public void close() throws IOException {
    try (Closeable cc = c;
         Closeable bb = b;
         Closeable aa = a;) {
        // do nothing
    }
}

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@AdamSkywalker如果b为null,则a和c将被关闭.

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@AdamSkywalker`try-with-resources`在Java中是空的安全:即使所有`cc`,`bb`和`aa`都为null - 没有任何失败.此外,不得使用未初始化或初始化不良的对象并抛出初始化异常.最好的情况是始终良好初始化的对象.