Java try with resources中出现死代码警告，但在翻译后的try catch finally中没有
下面的代码使用Java8中引入的构造。occasionalythrow（）方法声明抛出一个OccasionalException，资源的close（）方法抛出一个CloseException。Eclipse（版本：Neon Release（4.6.0），构建id:20160613-1800）在标有//dead code的行上添加了一条警告，指出分支是死代码。Eclipse隐式地确认标有//alive code的行不是死代码Java try with resources中出现死代码警告，但在翻译后的try catch finally中没有,java,eclipse,try-with-resources,Java,Eclipse,Try With Resources,下面的代码使用Java8中引入的构造。occasionalythrow（）方法声明抛出一个OccasionalException，资源的close（）方法抛出一个CloseException。Eclipse（版本：Neon Release（4.6.0），构建id:20160613-1800）在标有//dead code的行上添加了一条警告，指出分支是死代码。Eclipse隐式地确认标有//alive code的行不是死代码 Object tryWithResources() throws Occ
Object tryWithResources() throws OccasionalException {
Object value = null;
try (Resource resource = new Resource()) {
occasionallyThrow();
value = new Object();
}
catch (CloseException e) {
if (value == null) {
// alive code
}
else {
// dead code
}
}
return value;
}
trypublic class TestTryWithResources {
/** Exception thrown by Resource's close() method */
@SuppressWarnings("serial")
static class CloseException extends Exception {}
/** AutoCloseable declared to throw a CloseException */
static class Resource implements AutoCloseable {
@Override
public void close() throws CloseException {}
}
/** An occasionally thrown exception */
@SuppressWarnings("serial")
static class OccasionalException extends Exception {}
/** Method declared to throw an occasional exception */
void occasionallyThrow() throws OccasionalException {}
/*
* Method using try-with-resources. Eclipse warns that the
* portion marked with "// dead code" is Dead code.
*/
Object tryWithResources() throws OccasionalException {
Object value = null;
try (Resource resource = new Resource()) {
occasionallyThrow();
value = new Object();
}
catch (CloseException e) {
if (value == null) {
// alive code
}
else {
// dead code
}
}
return value;
}
/*
* Method not using try-with-resources. This is the translation
* of the try-with-resources in tryWithResources, according to
* [14.20.3 try-with-resources][1]. Eclipse does not warn about
* any of the code being Dead code.
*
* [1]: https://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.20.3
*/
Object expandedTry() throws OccasionalException {
Object value = null;
try {
Resource resource = new Resource();
Throwable $primary = null;
try {
occasionallyThrow();
value = new Object();
}
catch (Throwable t) {
$primary = t;
throw t;
}
finally {
if (resource != null) {
if ($primary != null) {
try {
resource.close();
}
catch (Throwable $suppressed) {
$primary.addSuppressed($suppressed);
}
}
else {
resource.close();
}
}
}
}
catch (CloseException e) {
if (value == null) {
// alive
}
else {
// alive
}
}
return value;
}
}
由于某种原因，静态代码分析器认为资源将在try声明之后立即关闭，而根据教程，资源将在语句之后关闭 try with resources语句确保在语句末尾关闭每个资源 因此，例如，如果您在值为（下面的代码）之后更改代码以使用资源，它不会警告您死代码（但是在EclipseLuna上测试） 更新 这是我在设置值后使用resource（在本例中为reader）测试的实际代码
Object val = null;
try (BufferedReader reader = new BufferedReader(new FileReader("C:\\file.txt"))) {
val = new Object();
System.out.println("got here");
reader.readLine();
}
catch(IOException e){
System.out.println("io ex");
if ( val == null){
}
else{
}
}
这并不能回答为什么Eclipse会生成警告，或者是否应该生成警告的问题，但这是一种解决方法，至少暂时消除了警告。您可以调用另一个方法，使用被测试的值以及异常，从该方法测试对象是否为null，然后执行任何需要执行的操作，而不是将条件放入catch块中：
Object tryWithResources() throws OccasionalException {
Object value = null;
try (Resource resource = new Resource()) {
occasionallyThrow();
value = new Object();
System.out.println(resource.toString());
}
catch (CloseException e) {
catchBlock(value, e); // call auxiliary method
}
return value;
}
void catchBlock(Object value, CloseException e) {
if (value == null) {
// then
}
else {
// else
}
}
也许是这样，尽管现在已经5年了……我不确定您是否能够捕获在关闭过程中抛出的异常，该异常是由try使用属于try块的catch块中的资源完成的。如果将CloseException更改为选中异常，会发生什么情况？如果您将捕获的内容另外移动到周围的尝试，会发生什么？@mm759首先回答中间的问题：CloseException是一个选中的异常。通过在这里将其定义为Exception的子类（而不是RuntimeException的子类），我确保了这一点。@mm759对于第一个问题，try with resources with a catch的行为由描述
try ResourceSpecification Block catch Finallytry{try ResourceSpecification Block}catch Finally Object val = null;
try (BufferedReader reader = new BufferedReader(new FileReader("C:\\file.txt"))) {
val = new Object();
System.out.println("got here");
reader.readLine();
}
catch(IOException e){
System.out.println("io ex");
if ( val == null){
}
else{
}
}
Object tryWithResources() throws OccasionalException {
Object value = null;
try (Resource resource = new Resource()) {
occasionallyThrow();
value = new Object();
System.out.println(resource.toString());
}
catch (CloseException e) {
catchBlock(value, e); // call auxiliary method
}
return value;
}
void catchBlock(Object value, CloseException e) {
if (value == null) {
// then
}
else {
// else
}
}