Summary
- The new interface AutoCloseable becomes the superinterface of Closeable.
- The try-with-resources statement is a try statement that declares one or more resources.
- A resource is an object that must be closed after the program is finished with it.
- The try-with-resources statement ensures that each resource is closed at the end of the statement.
- Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.
From: http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html
See also:
http://www.slideshare.net/alsdias/savedfiles?s_title=new-features-of-jdk-7&user_login=denizoguz
Example
Follow the comments on the code below, a full example to show the suppressed exception.
package exception.java7;
import java.io.Closeable;
import java.io.IOException;
/**
* exception.java7.Autocloseable_main.java<br>
* project: javaLab<br>
* <br>
* target: java 7 AutoCloseable example with suppressed exception. <br>
*/
public class Autocloseable_main {
public Autocloseable_main() {
}
/**
* @param args
*/
public static void main(String[] args) {
//event1();
event2();
}
/**
* <pre>
* Event1's output:
*
* [INFO]: opening a resource
* [INFO]: event1(): doing something
* [INFO]: closing a resource
* exception.java7.AppException: [WARN]: application failure.
* at exception.java7.Autocloseable_main.event1(Autocloseable_main.java:40)
* at exception.java7.Autocloseable_main.main(Autocloseable_main.java:31)
* Suppressed: exception.java7.AException: [ERROR]: resource failure.
* at exception.java7.AResource.close(Autocloseable_main.java:77)
* at exception.java7.Autocloseable_main.event1(Autocloseable_main.java:41)
* ... 1 more
*
* </pre>
*/
public static void event1() {
try (AResource resource = new AResource(false);) {
System.out.println("[INFO]: event1(): doing something");
if(!resource.success) throw new AppException("[WARN]: application failure.");
} catch (AException | AppException e) {
e.printStackTrace();
}
}
/**
* <pre>
* Event2's output:
*
* [INFO]: opening a resource
* [INFO]: event2(): doing something
* [INFO]: closing a resource
* exception.java7.AException: [ERROR]: resource failure.
* at exception.java7.AResource.close(Autocloseable_main.java:91)
* at exception.java7.Autocloseable_main.event2(Autocloseable_main.java:66)
* at exception.java7.Autocloseable_main.main(Autocloseable_main.java:32)
*
* </pre>
*/
public static void event2() {
try (AResource resource = new AResource(false);) {
System.out.println("[INFO]: event2(): doing something");
if(resource.success) throw new AppException("[ERROR]: application failure.");
} catch (AException | AppException e) {
e.printStackTrace();
}
}
}
class AResource implements Closeable {
boolean success = false;
public AResource() {
System.out.println("[INFO]: opening a resource");
}
public AResource(boolean success) {
System.out.println("[INFO]: opening a resource");
this.success = success;
}
@Override
public void close() throws AException {
System.out.println("[INFO]: closing a resource");
boolean notdone = true;
if (notdone) {
throw new AException("[ERROR]: resource failure.");
}
}
}
class AException extends IOException {
private static final long serialVersionUID = 1L;
public AException(String msg) {
super(msg);
}
}
class AppException extends Exception {
private static final long serialVersionUID = 1L;
public AppException(String msg) {
super(msg);
}
}
