Basic Cleaner Example

by: Ethan McCue

```java import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.lang.ref.Cleaner;

public final class HasResource implements AutoCloseable { // This has a Thread backing it so you want to share your cleaner across the whole lib private static final Cleaner CLEANER = Cleaner.create();

private final FileOutputStream outputStream;
private final Cleaner.Cleanable cleanable;

// You don't want your cleaner task to be a lambda so you don't accidentally capture a
// ref. to the wrapping object.
private static final class CleanerTask implements Runnable {
    private final FileOutputStream outputStream;

    private CleanerTask(FileOutputStream outputStream) {
        this.outputStream = outputStream;
    }

    @Override
    public void run() {
        try {
            this.outputStream.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

public HasResource() {
    try {
        this.outputStream = new FileOutputStream("ex.csv");
    } catch (FileNotFoundException e) {
        throw new RuntimeException(e);
    }
    this.cleanable = CLEANER.register(this, new CleanerTask(this.outputStream));
}

@Override
public void close() {
    // This has "at most once" semantics so if they close it the cleaner won't run your cleanup logic a second time
    this.cleanable.clean();
}

}



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