Introduction

• In previous topics, we have learned about the finally block which is used to execute cleanup code and release resources like files, database connections, or network streams.
• But managing resources manually can be error-prone and lead to resource leaks if not handled properly.
• Also we have write a lot of boilerplate code to ensure resources are closed properly.
• To address these issues, Java 7 introduced the try-with-resources.

• Definition:
  • Try-With-Resources is a feature introduced in Java 7 that allows you to declare resources in the try statement.
  • These resources are automatically closed at the end of the try block, eliminating the need for a finally block for cleanup.
    • A resource is any object that implements the AutoCloseable or Closeable interface (like FileInputStream, BufferedReader, Scanner, Connection etc.).

• Use:
  • Automatically closes resources after use, avoiding resource leaks.
  • Reduces boilerplate code, no need for explicit finally blocks for closing.
  • Makes code cleaner, safer and more readable.
  • Ensures exception-safe resource management, even if exceptions occur in the try block.

• Syntax:

  • try (ResourceType resource = new ResourceType())
    {
        // use the resource
    } 
    catch (ExceptionClassType e)
    {
        // handle exception
    }

  • Multiple resources can be declared using semicolon ; separation

    try ( ResourceType1 res1 = new ResourceType1();
           ResourceType2 res2 = new ResourceType2() )
    {
        // use resources
    }
    catch (ExceptionClassType e)
    {
        // handle exception
    }

• Example:

  • import java.io.BufferedReader;
    import java.io.FileReader;
    import java.io.IOException;
    
    public class TryWithResourcesDemo
    {
        public static void main(String[] args)
        {
            System.out.println("----- App Started -----");
    
            // try-with-resources automatically closes BufferedReader
            try (BufferedReader br = new BufferedReader(new FileReader("test.txt")))
            {
                String line;
                while ((line = br.readLine()) != null)
                {
                    System.out.println(line);
                }
            } 
            catch (IOException e)
            {
                System.out.println("IOException occurred: " + e);
            }
    
            System.out.println("----- App Finished Successfully -----");
        }
    }

    Output:

    ----- App Started -----
    Line 1 from test.txt
    Line 2 from test.txt
    ...
    ----- App Finished Successfully -----

Points to remember for Try-With-Resource block:

1. No need for explicit finally block to close the resource.
2. Resources must implement AutoCloseable or Closeable.
3. Multiple resources can be managed in a single try statement.
4. Exceptions during resource closing are suppressed but can be retrieved using Throwable.getSuppressed().