Reading and writing files in Java 7 using the new try-with-resources construct relieves the developer of the task of correctly closing streams. Below you can find two example methods:
To write a file:
protected boolean write(String name, String text) {
boolean completed;
try (Writer writer =
new BufferedWriter(
new OutputStreamWriter(new FileOutputStream(name), "utf-8")))
{
writer.write(text);
completed = true;
} catch (IOException e) {
completed = false;
logger.log(Level.SEVERE, "", e);
}
return completed;
}
And to read its contents:
public String read(String name) {
String text = null;
try (BufferedReader buffer = new BufferedReader(new FileReader(name))) {
StringBuilder string = new StringBuilder();
String line = buffer.readLine();
while (line != null) {
string.append(line).append(System.lineSeparator());
line = buffer.readLine();
}
text = string.toString();
} catch (FileNotFoundException e) {
logger.log(Level.SEVERE, "", e);
} catch (IOException e) {
logger.log(Level.SEVERE, "", e);
}
return text;
}
When the try block ends the stream will be closed automatically. This is possible because the classes used in the try-with-resources block implement the Java interface java.lang.AutoCloseable .
All classes that implement this interface can be used within try-with-resources.
The AutoCloseable interface has only one method, close().
public interface AutoCloseable {
public void close() throws Exception;
}
Implementing AutoCloseable on one of our objects does not require much effort, as can be seen from the example code below:
public class AutoClosableExampleObject implements AutoCloseable {
@Override
public void close() throws Exception {
//do stuff and close
}
}
If we don’t want to catch the exception, just omit the catch part of the block, and it will propagate as if it were unhandled (just a try without a catch and without a finally). To be honest, the code above could have benefited from other new features in version 7, such as catch with multiple exception handling, but more on that in a future post.