27 May 2013

New Features Of Exception Handling In Java1.7

Apart of normal exception handling some new features have been introduced in java 1.7. 

Handling more than one exception with a single catch block:-
In Java SE 7 and later, a single catch block can handle more than one type of exception. This feature can reduce code duplication and lessen the temptation to catch an overly broad exception.
In the catch clause, specify the types of exceptions that block can handle, and separate each exception type with a vertical bar (|):

catch (IOException|SQLException ex) {
    throw ex;

Note: If a catch block handles more than one exception type, then the catch parameter is implicitly final. In this example, the catch parameter ex is final and therefore you cannot assign any values to it within the catch block.

The try-with-resource statement:-

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. Thetry-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.
The following example reads the first line from a file. It uses an instance of BufferedReader to read data from the file. BufferedReader is a resource that must be closed after the program is finished with it:

static String readFirstLineFromFile(String path) throws IOException {
    try (BufferedReader) br = new BufferedReader(new FileReader(path))) {
          return br.readLine();

In this example, the resource declared in the try-with-resources statement is a BufferedReader. The declaration statement appears within parentheses immediately after thetry keyword. The class BufferedReader, in Java SE 7 and later, implements the interface java.lang.AutoCloseable. Because the BufferedReader instance is declared in a try-with-resource statement, it will be closed regardless of whether the try statement completes normally or abruptly. 

You may declare one or more resources in a try-with-resources statement. 


try (
        java.util.zip.ZipFile zf = new java.util.zip.ZipFile(zipFileName);
        java.io.BufferedWriter writer = java.nio.file.Files.newBufferedWriter(outputFilePath, charset)
    ) {
         // code that uses the resources goes here.

Suppressed Exceptions:-

An exception can be thrown from the block of code associated with the try-with-resources statement. If an exception is thrown from the try block and one or more exceptions are thrown from the try-with-resources statement, then those exceptions thrown from the try-with-resources statement are suppressed, and the exception thrown by the block is the one that is thrown by the method. You can retrieve these suppressed exceptions by calling the Throwable.getSuppressed method from the exception thrown by the try block.


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