java 7中的try catch除了之前谈到的新特性外，本文简单来例子小结下，其实还是有不少地方要注意的，首先看一个典型的代码：
先来两个异常类：
1. public class ExceptionA extends
2. public
3. super(message);
4. }
5. }
6. public class ExceptionB extends
7. public
8. super(message);
9. }
10. }
public class ExceptionA extends Exception{
public ExceptionA(String message){
super(message);
}
}
public class ExceptionB extends Exception{
public ExceptionB(String message){
super(message);
}
} 再创建一个资源类oldresource，如下：
1.
2. public class
3. public void doSomeWork(String work) throws
4. "Doing: "+work);
5. throw new ExceptionA("Exception occured while doing work");
6. }
7. public void close() throws
8. "Closing the resource");
9. throw new ExceptionB("Exception occured while closing");
10. }
11. }
public class OldResource{
public void doSomeWork(String work) throws ExceptionA{
System.out.println("Doing: "+work);
throw new ExceptionA("Exception occured while doing work");
}
public void close() throws ExceptionB{
System.out.println("Closing the resource");
throw new ExceptionB("Exception occured while closing");
}
}
public class OldResource{
public void doSomeWork(String work) throws ExceptionA{
System.out.println("Doing: "+work);
throw new ExceptionA("Exception occured while doing work");
}
public void close() throws ExceptionB{
System.out.println("Closing the resource");
throw new ExceptionB("Exception occured while closing");
}
} 我们开始使用之：
1. public class
2. public static void
3. null;
4. try
5. new
6. "Writing an article");
7. catch
8. "Exception Message: "+
9. " Exception Type: "+e.getClass().getName());
10. finally{
11. try
12. res.close();
13. catch
14. "Exception Message: "+
15. " Exception Type: "+e.getClass().getName());
16. }
17. }
18. }
19. }
public class OldTry {
public static void main(String[] args) {
OldResource res = null;
try {
res = new OldResource();
res.doSomeWork("Writing an article");
} catch (Exception e) {
System.out.println("Exception Message: "+
e.getMessage()+" Exception Type: "+e.getClass().getName());
} finally{
try {
res.close();
} catch (Exception e) {
System.out.println("Exception Message: "+
e.getMessage()+" Exception Type: "+e.getClass().getName());
}
}
}
}
public class OldTry {
public static void main(String[] args) {
OldResource res = null;
try {
res = new OldResource();
res.doSomeWork("Writing an article");
} catch (Exception e) {
System.out.println("Exception Message: "+
e.getMessage()+" Exception Type: "+e.getClass().getName());
} finally{
try {
res.close();
} catch (Exception e) {
System.out.println("Exception Message: "+
e.getMessage()+" Exception Type: "+e.getClass().getName());
}
}
}
} 看输出：
Doing: Writing an article
Exception Message: Exception occured while doing work Exception Type: javaapplication4.ExceptionA
Closing the resource
Exception Message: Exception occured while closing Exception Type: javaapplication4.ExceptionB
再来看java 7中的新写法，代码如下：
1. public class NewResource implements
2. String closingMessage;
3.
4. public
5. this.closingMessage = closingMessage;
6. }
7.
8. public void doSomeWork(String work) throws
9. System.out.println(work);
10. throw new ExceptionA("Exception thrown while doing some work");
11. }
12. public void close() throws
13. System.out.println(closingMessage);
14. throw new ExceptionB("Exception thrown while closing");
15. }
16.
17. public void doSomeWork(NewResource res) throws
18. "Wow res getting res to do work");
19. }
20. }
public class NewResource implements AutoCloseable{
String closingMessage;
public NewResource(String closingMessage) {
this.closingMessage = closingMessage;
}
public void doSomeWork(String work) throws ExceptionA{
System.out.println(work);
throw new ExceptionA("Exception thrown while doing some work");
}
public void close() throws ExceptionB{
System.out.println(closingMessage);
throw new ExceptionB("Exception thrown while closing");
}
public void doSomeWork(NewResource res) throws ExceptionA{
res.doSomeWork("Wow res getting res to do work");
}
} 在JAVA 7中，要自动在try catch中利用到新特性，想不写那么多东西就关闭资源，则可以编写实现 AutoCloseable类的，则都可以利用该特性了。
在主程序中调用：
1. public class
2. public static void
3. try(NewResource res = new NewResource("Res1 closing")){
4. "Listening to podcast");
5. catch(Exception e){
6. "Exception: "+
7. " Thrown by: "+e.getClass().getSimpleName());
8. }
9. }
10. }
public class TryWithRes {
public static void main(String[] args) {
try(NewResource res = new NewResource("Res1 closing")){
res.doSomeWork("Listening to podcast");
} catch(Exception e){
System.out.println("Exception: "+
e.getMessage()+" Thrown by: "+e.getClass().getSimpleName());
}
}
} 输出结果为：
Listening to podcast
Res1 closing
Exception: Exception thrown while doing some work Thrown by: ExceptionA
大家可以思考下为什么这样输出，在新特性中，资源的自动关闭调用了close(),而
NewResource res = new NewResource("Res1 closing")){
已经为closingMessage赋值了，而最后的Exception e是输出了，suprred掉了
exception a和exception b的输出。
再看一个多层嵌套的try catch例子
1. public class
2. public static void
3. try(NewResource res = new NewResource("Res1 closing");
4. new NewResource("Res2 closing")){
5. try(NewResource nestedRes = new NewResource("Nestedres closing")){
6. nestedRes.doSomeWork(res2);
7. }
8. catch(Exception e){
9. "Exception: "+
10. " Thrown by: "+e.getClass().getSimpleName());
11. }
12.
13. }
14. }
public class TryWithRes {
public static void main(String[] args) {
try(NewResource res = new NewResource("Res1 closing");
NewResource res2 = new NewResource("Res2 closing")){
try(NewResource nestedRes = new NewResource("Nestedres closing")){
nestedRes.doSomeWork(res2);
}
} catch(Exception e){
System.out.println("Exception: "+
e.getMessage()+" Thrown by: "+e.getClass().getSimpleName());
}
}
} 输出：
Wow res getting res to do work
Nestedres closing
Res2 closing
Res1 closing
Exception: Exception thrown while doing some work Thrown by: ExceptionA
可以看到，后声明的资源上被最先CLOSE掉的，这里各自原先的exception都被supressed掉了。还可以用e.getSuppressed() 把屏蔽掉的exception都放来，比如
1. public class
2. public static void
3. try(NewResource res = new NewResource("Res1 closing");
4. new NewResource("Res2 closing")){
5. try(NewResource nestedRes = new NewResource("Nestedres closing")){
6. nestedRes.doSomeWork(res2);
7. }
8. catch(Exception e){
9. "Exception: "+
10. " Thrown by: "+e.getClass().getSimpleName());
11. if (e.getSuppressed() != null){
12. for
13. System.out.println(t.getMessage()+
14. " Class: "+t.getClass().getSimpleName());
15. }
16. }
17. }
18.
19. }
20. }
public class TryWithRes {
public static void main(String[] args) {
try(NewResource res = new NewResource("Res1 closing");
NewResource res2 = new NewResource("Res2 closing")){
try(NewResource nestedRes = new NewResource("Nestedres closing")){
nestedRes.doSomeWork(res2);
}
} catch(Exception e){
System.out.println("Exception: "+
e.getMessage()+" Thrown by: "+e.getClass().getSimpleName());
if (e.getSuppressed() != null){
for (Throwable t : e.getSuppressed()){
System.out.println(t.getMessage()+
" Class: "+t.getClass().getSimpleName());
}
}
}
}
}
输出显示：
Wow res getting res to do work
Nestedres closing
Res2 closing
Res1 closing
Exception: Exception thrown while doing some work Thrown by: ExceptionA
Exception thrown while closing Class: ExceptionB
Exception thrown while closing Class: ExceptionB
Exception thrown while closing Class: ExceptionB