this.getSourceViewer().getTextWidget().addKeyListener(
        new KeyListener() {
            public void keyReleased(KeyEvent e) {
            }
            public void keyPressed(KeyEvent e) {
                if (e.keyCode == SWT.CR) {
                    // call cli method here
                    System.out.println("Executing the command");
                    callCli();
                }
            }
        });

    public class CliConfiguration extends SourceViewerConfiguration {
	private boolean contentAssistSessionStarted = false;
	private boolean contentAssistSessionEnded = false;
	@Override
	public IContentAssistant getContentAssistant(ISourceViewer sourceViewer) {
		ContentAssistant assistant = new ContentAssistant();
                ...
		assistant.addCompletionListener(new ICompletionListener() {
			public void selectionChanged(ICompletionProposal proposal,boolean smartToggle) {
			}
			public void assistSessionStarted(ContentAssistEvent event) {
				contentAssistSessionStarted = true;
				contentAssistSessionEnded = false;
			}

			public void assistSessionEnded(ContentAssistEvent event) {
				contentAssistSessionEnded = true;
				contentAssistSessionStarted = true;
			}
		});
		return assistant;
	}


public class CliCmdInputEditor extends TextEditor {
	@Override
	public void createPartControl(Composite parent) {
		super.createPartControl(parent);
		this.getSourceViewer().getTextWidget().addVerifyKeyListener(new VerifyKeyListener() {
			public void verifyKey(VerifyEvent e) {
				if (e.character == SWT.CR || e.character == SWT.LF) {
					if (cliConfiguration.hitEnterKeyInContentAssit()) {
						// do nothing, and allow enter key
						System.out
								.println("the enter key happened in content assist");
						return;
					}
                                        // cancel enter operation, and call cli method.
					System.err.println("call cli method here");
					e.doit = false;
				}
			}
		});
	}

public class CliCmdInputEditor extends TextEditor {
	@Override
	public void createPartControl(Composite parent) {
		super.createPartControl(parent);
		this.getSourceViewer().getTextWidget().addVerifyKeyListener(new VerifyKeyListener() {
			public void verifyKey(VerifyEvent e) 
				if (e.doit == false) {
					return;
				}
				if (e.character == SWT.CR || e.character == SWT.LF) {
                                        // don't output newline here
                                        e.doit = false;
					System.err.println("call cli method here");
				}
			}
		});