Question

我有以下与java 1.7兼容的代码，但是，我需要它与java 1.6兼容。目前，此代码出现以下错误：try-with-resources is not supported in -source 1.6

代码如下所示：

    try (QueryExecution qexec = QueryExecutionFactory.create(query, input.getModel())) {
        // Some other code
        while (results.hasNext()) {
            // do something
        }
        return something;
    }

我需要更改什么才能使其适用于java 1.6？

Answer 1

真正的答案：

这里真正的答案是使用Java 7或8 。 Java 6很老了。 Java 7出现四年之前; Java 8，差不多一年半了。

只有在非常非常好的原因导致您不能这样做时，才能继续阅读。： - ）

<强> TL; DR

具体示例可以简单地说：

QueryExecution qexec = QueryExecutionFactory.create(query, input.getModel());
Throwable thrown = null;
try {
    // Some other code
    while (results.hasNext()) {
        // do something
    }
    return something;
}
catch (Throwable t) {
    thrown = t; // Remember we're handling an exception
    throw t;
}
finally {
    try {
        qexec.close();
    }
    catch (Throwable t) {
        if (thrown == null) {
            // Not handling an exception, we can rethrow
            throw t;
        }
        else {
            // Log it or something, you can't allow it to
            // throw because there's *already* an exception
            // being thrown and you'll hide it. This is why
            // Java 7 added Throwable#addSuppressed.
        }
    }
}

但那是因为这是一个非常简单的案例。如果还有其他资源需要关闭（例如results？）或者你在代码本身处理一些异常，那就更复杂了。

更通用的形式是;

SomeResource r1 = null;
Throwable thrown = null;
try {
    r1 = new SomeResource();

    SomeOtherResource r2 = null;
    try {
        r2 = new SomeOtherResource();
        // use them
        return something;
    }
    catch (Throwable t) {
        thrown = t; // Remember we're handling an exception
        throw t;
    }
    finally {
        try {
            r2.close();
        }
        catch (Throwable t) {
            if (thrown == null) {
                // Not handling an exception, we can rethrow
                throw t;
            }
            else {
                // Log it or something, you can't allow it to
                // throw because there's *already* an exception
                // being thrown and you'll hide it. This is why
                // Java 7 added Throwable#addSuppressed.
            }
        }
    }
}
catch (Throwable t) {
    thrown = t; // Remember we're handling an exception
    throw t;
}
finally {
    try {
        r1.close();
    }
    catch (Throwable t) {
        if (thrown == null) {
            // Not handling an exception, we can rethrow
            throw t;
        }
        else {
            // Log it or something
        }
    }
}

你可能想要一些实用程序库函数来帮助解决这个问题，否则它是一个很多的样板文件。在过去我知道异常已经发生的情况下，我曾经做过“沉默”的事情。

详情：§14.20.3 of the JLS及其小节涵盖了这一点：

一个简单的try-with-resources：

try ({VariableModifier} R Identifier = Expression ...)
    Block

转换为：

{
    final {VariableModifierNoFinal} R Identifier = Expression;
    Throwable #primaryExc = null;

    try ResourceSpecification_tail
        Block
    catch (Throwable #t) {
        #primaryExc = #t;
        throw #t;
    } finally {
        if (Identifier != null) {
            if (#primaryExc != null) {
                try {
                    Identifier.close();
                } catch (Throwable #suppressedExc) {
                    #primaryExc.addSuppressed(#suppressedExc);
                }
            } else {
                Identifier.close();
            }
        }
    }
}

您必须删除addSuppressed部分，因为Throwable在JDK6中没有。{/ p>

扩展try-with-resources：

try ResourceSpecification
    Block
[Catches]
[Finally]

转换为：

try {
    try ResourceSpecification
        Block
}
[Catches]
[Finally]

......那里

try ResourceSpecification
    Block

...被简单try-with-resources变成的大事所取代，所以整个事情变成了：

try {
    {
        final {VariableModifierNoFinal} R Identifier = Expression;
        Throwable #primaryExc = null;

        try ResourceSpecification_tail
            Block
        catch (Throwable #t) {
            #primaryExc = #t;
            throw #t;
        } finally {
            if (Identifier != null) {
                if (#primaryExc != null) {
                    try {
                        Identifier.close();
                    } catch (Throwable #suppressedExc) {
                        #primaryExc.addSuppressed(#suppressedExc);
                    }
                } else {
                    Identifier.close();
                }
            }
        }
    }
}
[Catches]
[Finally]

...这就是我们非常喜欢try-with-resources陈述的原因。

Answer 2

我需要更改什么才能使其适用于java 1.6？

请尝试以下代码：

QueryExecution qexec = null; 
try {
  qexec = QueryExecutionFactory.create(query, input.getModel()));
  // Some other code
  while (results.hasNext()) {
      // do something
  }
  return something;
} finally {
    if (qexec != null){
        qexec.close();
    }
}

最重要的部分：必须在finally块中手动关闭流。

请注意，Oracle Java SE 6现在甚至Oracle Java SE 7都已达到EoL。因此，如果您正在使用Oracle的实施并且没有相应的支持合同，那么强烈建议您升级到Java SE 8

使代码java 1.6兼容（-source 1.6中不支持try-with-resources）

2 个答案: