blocks|key|108499|text|它不会catch任何东西。但是它确实finally关闭了所有的资源。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|108500|finally会阻止are+run+even+when+an+Error+is+thrown。|108501|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/464098/does-a-finally-block-always-run^0|3|5|I|7|0|0|7|A|10|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|H|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

It does not <code>catch</code> anything. But it does <code>finally</code> close all resources.

<code>finally</code> blocks <a href="https://stackoverflow.com/questions/464098/does-a-finally-block-always-run">are run even when an Error is thrown</a>.

blocks|key|108334|text|您的误解:使用资源尝试不是做的捕获。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|108335|它做了一个最终的，因此“问题”的种类并不重要。|108336|有关更多信息，请参阅JLS！|108337|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20.3^0|B|2|0|0|A|3|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|V|8|@]|D|@$9|W|A|X|1|Y]]|E|$]]|$1|J|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]]]

Misconception on your end: try-with-resources does not do a catch.

It does a final finally, therefore the kind of "problem" doesn't matter.

See the <a href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20.3" rel="nofollow noreferrer">JLS</a> for further information!

blocks|key|2863518|text|尝试使用资源本身并不能捕获任何东西。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2863519|但是，您可以将catch块附加到try-with-resources块的末尾，以捕获您喜欢的任何类型的Throwable：|offset|length|style|CODE|2863520|try+(UserCreatorTestUtil+userCreatorTestUtil+=+new+UserCreatorTestUtil())+{
++//+...+Whatever
}+catch+(RuntimeException+e)+{
++//+Handle+e.
}+catch+(Exception+%7C+Throwable+t)+{
++//+Handle+t.
}|code-block|syntax|javascript|2863521|entityMap^0|0|7|5|1F|9|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@$D|Q|E|R|F|G]|$D|S|E|T|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|U|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

Try-with-resources don't catch anything in and of themselves.

However, you can attach a <code>catch</code> block to the end of the try-with-resources block, to catch whatever types of <code>Throwable</code> you like:

<pre><code>try (UserCreatorTestUtil userCreatorTestUtil = new UserCreatorTestUtil()) {
 // ... Whatever
} catch (RuntimeException e) {
 // Handle e.
} catch (Exception | Throwable t) {
 // Handle t.
}
</code></pre>

blocks|key|2652313|text|基本try-with-resources语句的伪代码是(参见Java+Language+Specification+§14.20.3.1)：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2652314|final+VariableModifiers_minus_final+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();
++++++++}
++++}
}|code-block|syntax|javascript|2652315|正如您所看到的，它捕获Throwable而不是包含Error的Exception，而只是为了获取主要异常，以便将关闭资源时发生的任何异常添加为受抑制的异常。|2652316|您还可以注意到，您的资源在finally块中被关闭，这意味着无论发生什么，、它们都将被关闭(当然，System.exit的情况除外，因为它终止了当前正在运行的Java+Virtual+Machine)，即使抛出Error或Throwable的任何子类也是如此。|BOLD|2652317|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20.3.1^0|U|12|U|12|0|0|0|B|9|P|5|V|9|0|D|7|1D|B|2X|5|33|9|11|8|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@$9|10|A|11|1|12]]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|O]]|D|@]|E|$]]|$1|P|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]]|Q|$R|$5|S|T|U|E|$V|W]]]]

The pseudo-code of a basic try-with-resources statement is (cf <a href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20.3.1" rel="nofollow noreferrer"><code>Java Language Specification §14.20.3.1</code></a>):

<pre><code>final VariableModifiers_minus_final 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();
 }
 }
}
</code></pre>

As you can see it catches <code>Throwable</code> not <code>Exception</code> which includes <code>Error</code> but only to get the primary exception in order to add as suppressed exceptions any exceptions that occurred while closing the resources.

You can also notice that your resources are closed in the <code>finally</code> block which means that they will be closed whatever happens (except in case of a <code>System.exit</code> of course as it terminates the currently running Java Virtual Machine) even in case an <code>Error</code> or any sub class of <code>Throwable</code> is thrown.

blocks|key|2652343|text|try-with-resources背后的想法是确保资源应该被关闭。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2652344|传统try-catch-finally语句的问题在于，假设您的try块抛出了一个异常；现在通常您将在finally块中处理该异常。|2652345|现在假设在finally块中也发生了异常。在这种情况下，try+catch抛出的异常是lost，并且在finally块中生成的异常被传播。|BOLD|2652346|try+{
++++//+use+something+that's+using+resource
++++//+e.g.,+streams
}+catch(IOException+e)+{
+++//+handle+
}+finally+{
++++stream.close();
++++//if+any+exception+occurs+in+the+above+line,+than+that+exception
++++//will+be+propagated+and+the+original+exception+that+occurred
++++//in+try+block+is+lost.
}|code-block|syntax|javascript|2652347|在try-with-resources中，资源的close()方法将被自动调用，如果close()抛出任何异常，则无法到达finally的其余部分，并且原始异常将丢失。|2652348|与此形成对比：|2652349|try+(InputStream+inputStream=+new+FileInputStream("C://test.txt")){
++++//+...+use+stream
}+catch(IOException+e)+{
+++//+handle+exception
}|2652350|在上面的代码片段中，close()方法被自动调用，如果该close()方法也生成了任何异常，那么该异常将自动被抑制。|2652351|另请参阅：Java+Language+Specification+14.20.3|2652352|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20.3^0|0|I|0|2|H|V|3|1E|7|0|17|4|1F|7|0|0|1|I|O|7|16|7|1P|7|0|0|0|A|7|S|7|0|5|Z|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1A|8|@$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1H|8|@$9|1I|A|1J|B|J]|$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|K|3|L|5|M|7|1M|8|@]|D|@]|E|$N|O]]|$1|P|3|Q|5|6|7|1N|8|@$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]|$9|1S|A|1T|B|C]|$9|1U|A|1V|B|C]]|D|@]|E|$]]|$1|R|3|S|5|6|7|1W|8|@]|D|@]|E|$]]|$1|T|3|U|5|M|7|1X|8|@]|D|@]|E|$N|O]]|$1|V|3|W|5|6|7|1Y|8|@$9|1Z|A|20|B|C]|$9|21|A|22|B|C]]|D|@]|E|$]]|$1|X|3|Y|5|6|7|23|8|@]|D|@$9|24|A|25|1|26]]|E|$]]|$1|Z|3|-4|5|6|7|27|8|@]|D|@]|E|$]]]|10|$11|$5|12|13|14|E|$15|16]]]]

The idea behind <code>try-with-resources</code> is to make sure that the resources should be closed.

The problem with conventional <code>try-catch-finally</code> statements is that let's suppose your <code>try</code> block throws an exception; now usually you'll handle that exception in <code>finally</code> block. 

Now suppose an exception occurs in finally block as well. In such a case, the exception thrown by try catch is lost and the exception generated in <code>finally</code> block gets propagated.

<pre><code>try {
 // use something that's using resource
 // e.g., streams
} catch(IOException e) {
 // handle 
} finally {
 stream.close();
 //if any exception occurs in the above line, than that exception
 //will be propagated and the original exception that occurred
 //in try block is lost.
}
</code></pre>

In <code>try-with-resources</code> the <code>close()</code> method of the resource will get automatically called, and if the <code>close()</code> throws any exception, the rest of the <code>finally</code> isn't reached, and the original exception is lost.

Contrast that with this:

<pre><code>try (InputStream inputStream= new FileInputStream("C://test.txt")){
 // ... use stream
} catch(IOException e) {
 // handle exception
}
</code></pre>

in the above code snippet, the <code>close()</code> method automatically gets called and if that <code>close()</code> method also generated any exception, than that exception will automatically get suppressed.

See also: <a href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20.3" rel="nofollow noreferrer">Java Language Specification 14.20.3</a>

I have some junit tests which create some resources which should also be closed.

One way to implement this logic is using the <code>@Before</code> and <code>@After</code> approach.

What I did was to encapsulate the creation in some utility class to be reused. For example:

<pre><code>class UserCreatorTestUtil implements AutoClosable {
 User create() {...}
 void close() {...}
}
</code></pre>

The whole point is for the object to close itself, rather than needing to remember to close it in <code>@After</code>.

The usage should be:

<pre><code>@Test
void test() {
 try (UserCreatorTestUtil userCreatorTestUtil = new UserCreatorTestUtil()) {
 User user = userCreatorTestUtil.create();
 // Do some stuff regarding the user's phone
 Assert.assertEquals("123456789", user.getPhone());
 }
}
</code></pre>

The problem is that junit's assert keyword throws an <code>Error</code> - not <code>Exception</code>.

Will the try-with-resource "catch" the <code>Error</code> and invoke the close method?

* Couldn't find the answer in the <a href="https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html" rel="noreferrer">try-with-resources documentation</a>.

Does Java's try-with-resources catch errors or just exceptions?

Java

我有一些junit测试，它们创建了一些也应该关闭的资源。实现此逻辑的一种方法是使用@Before和@After方法。我所做的是将创建封装在某个实用程序类中以供重用。例如：class UserCreatorTestUtil implements AutoClosable {  User create() {...}  v...

问Java的try-with-resources是捕获错误还是仅捕获异常？
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