Tutorial 29: Java 7 Try with Resources

Remember when we learnt how to read a file using FileReader? Well, I told you and you’d agree that that tutorial was a bit difficult. There were so many exceptions that we had to throw and catch and the program did not look neat in any way whatsoever.

In Java 7, Oracle introduced a new feature called “try with resources.” What try with resources means is that you can write the code that was originally inside the curly braces of the try block of the try-catch block inside round brackets just after the word “try”, but before the opening curly brace of the try block.

However, remember that when opening the file, we created a file object to which we passed the address of the file to its constructor like this:

File file = new File (“C:/Users/Mukami/Desktop/Document1.txt”);

Then, we created a FileReader object that would read the file and then passed the file object to its constructor like this:

FileReader fileReader1 = new FileReader(file);

Then, we created a BufferedReader object to read the file line by line and passed the FileReader object to its constructor like this:

BufferedReader bufferedReader1 = new BufferedReader(fileReader1);

All the above steps could be done in one line like this:

BufferedReader bufferedReader1 = new BufferedReader(new FileReader(file));

So in try with resources, what we do is surround the above line with round braces like this and place it just after the try keyword.

try(BufferedReader bufferedReader1 = new BufferedReader(new FileReader(file))) {

}

Then, we surround try with the catch blocks like this:

try(BufferedReader bufferedReader1 = new BufferedReader(new FileReader(file))) {

} catch (FileNotFoundException e) {

            System.out.println(“Could not open the file”);

} catch (IOException e) {

            System.out.println(“Cannot read the file”);

}

Now, we can add the functionality to read the file within the try block like this:

try(BufferedReader bufferedReader1 = new BufferedReader(new FileReader(file))) {

            String line;

            while((line = bufferedReader1.readLine()) != null) {

                        System.out.println(line);

            }

} catch (FileNotFoundException e) {

System.out.println(“Could not find file”);

} catch (IOException e) {

            System.out.println (“Cannot read the file”);

}

Figure 1: Reading a text file using the try with resources Java syntax

Now we have a program that reads and closes a file. Remember that in the previous tutorial, we had to call bufferedReader1.close(). However, with try with resources, Java will automatically close the file handle for you. This really makes your code neater than in the previous tutorial.

Note that you can use try with resources anywhere where you would use a try-catch block, and this doesn’t necessarily mean that it can only be used when we want to open and read contents of a file. This was just an example.

Also, the line: BufferedReader bufferedReader1 = new BufferedReader(new FileReader(file)) is just a way to shorten your code and use a few less lines. It’s doesn’t mean that to use the try with resources feature, that we have to do this to every code.