In Java 7, the catch block has been improved to handle multiple exceptions in a single catch block. If you are catching multiple exceptions and they have similar code, then using this feature will reduce code duplication. Let’s understand the Java catch multiple exceptions feature with an example.
Java Catch Multiple Exceptions
Before Java 7, we used to catch multiple exceptions one by one as shown below.
catch (IOException ex) {
logger.error(ex);
throw new MyException(ex.getMessage());
catch (SQLException ex) {
logger.error(ex);
throw new MyException(ex.getMessage());
}In Java 7, we can catch both these exceptions in a single catch block as:
catch(IOException | SQLException ex){
logger.error(ex);
throw new MyException(ex.getMessage());
}If a catch block handles multiple exceptions, you can separate them using a pipe (|) and in this case, the exception parameter (ex) is final, so you can’t change it. The byte code generated by this feature is smaller and reduces code redundancy.
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Java Rethrow Exception
Another improvement is done in Compiler analysis of rethrown exceptions. Java rethrow exception allows you to specify more specific exception types in the throws clause of a method declaration. Let’s see this with a small example:
package com.journaldev.util;
public class Java7MultipleExceptions {
public static void main(String[] args) {
try{
rethrow("abc");
}catch(FirstException | SecondException | ThirdException e){
System.out.println(e.getMessage());
}
}
static void rethrow(String s) throws FirstException, SecondException,
ThirdException {
try {
if (s.equals("First"))
throw new FirstException("First");
else if (s.equals("Second"))
throw new SecondException("Second");
else
throw new ThirdException("Third");
} catch (Exception e) {
throw e;
}
}
static class FirstException extends Exception {
public FirstException(String msg) {
super(msg);
}
}
static class SecondException extends Exception {
public SecondException(String msg) {
super(msg);
}
}
static class ThirdException extends Exception {
public ThirdException(String msg) {
super(msg);
}
}
}As you can see in the rethrow method, the catch block is catching Exception but it’s not part of the throws clause. The Java 7 compiler analyzes the complete try block to check what types of exceptions are thrown and then rethrown from the catch block. Note that this analysis is disabled if you change the catch block argument.
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