NetBeans Code Snippet Module Tutorial

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This tutorial demonstrates how to create and add code snippets to the HTML/JSP Component Palette. Code snippets are small pieces of code that can be dragged from a component palette and dropped in the Source Editor. They serve to speed up coding. The HTML/JSP Component Palette has several code snippets already, but you might want to add some additional ones and share them with others.

This document uses NetBeans Platform 7.1 and NetBeans IDE 7.1. If you are using an earlier version, see the previous version of this document.

Introduction to Code Snippets

To create a code snippet, you use the NetBeans Palette API. A code snippet requires the following files:

  • A Java class that defines the piece of code to be dragged into the Source Editor.

  • A display name for the palette item.

  • A tooltip for the palette item.

  • A 16x16 pixel image for the 'Small Icon' display.

  • A 32x32 pixel image for the 'Big Icon' display.

After you have created or added the above files to the NetBeans module, you declare them in a resource declaration XML file, which you register in the NetBeans System Filesystem by using the layer.xml file.

Setting up the Module Project

Before you start writing the module, you have to make sure you that your project is set up correctly. The IDE provides a wizard that sets up all the basic files needed for a module.

Creating the Module Project

  1. Choose File > New Project (Ctrl+Shift+N). Under Categories, select NetBeans Modules. Under Projects, select Module. Click Next.

  1. In the Name and Location panel, type Newhtmlsnippets in the Project Name field. Change the Project Location to any directory on your computer. Click Next.

  1. In the Basic Module Configuration panel, type org.netbeans.modules.newhtmlsnippets in Code Name Base. Click Finish.

The IDE creates the Newhtmlsnippets project. The project contains all of your sources and project metadata, such as the project’s Ant build script. The project opens in the IDE. You can view its logical structure in the Projects window (Ctrl-1) and its file structure in the Files window (Ctrl-2).

Specifying the Module’s Dependencies

You will need to use several classes that belong to the NetBeans APIs. Each has to be declared as a module dependency. Use the Project Properties dialog box for this purpose, as described below.

  1. In the Projects window, right-click the Newhtmlsnippets project node and choose Properties. In the Project Properties dialog box, click Libraries.

1. For each of the following, click "Add…​", select the name from the Module list, and then click OK to confirm it:

  • Common Palette

  • Text API

  • Utilities API

Click OK to exit the Project Properties dialog box.

  1. In the Projects window, expand the Important Files node, double-click the Project Metadata node, and note that the APIs you selected have been declared as module dependencies.

Coding the Code Snippet

In this section, you create BR.java , which defines a code snippet for an HTML line break. By implementing the ActiveEditorDrop class, you let the NetBeans APIs provide the infrastructure for a palette item for NetBeans editors. You also create HTMLPaletteUtilities.java , which defines the insertion of the tag in the editor.

Creating the Code Snippet

  1. Right-click the org.netbeans.modules.newhtmlsnippets node and choose New > Java Class. Type BR in Class Name, make sure that the org.netbeans.modules.newhtmlsnippets package is selected in the Package drop-down list, and click Finish.

  1. Replace the default content of the BR.java file with the following:

package org.netbeans.modules.newhtmlsnippets;

import javax.swing.text.BadLocationException;
import javax.swing.text.JTextComponent;
import org.netbeans.modules.newhtmlsnippets.HTMLPaletteUtilities;
import  link:http://bits.netbeans.org/dev/javadoc/org-openide-text/org/openide/text/ActiveEditorDrop.html[org.openide.text.ActiveEditorDrop];

public class BR implements  link:http://bits.netbeans.org/dev/javadoc/org-openide-text/org/openide/text/ActiveEditorDrop.html[ActiveEditorDrop] {

    public BR() {
    }

    private String createBody() {
        String Br = "<br>";
        return Br;
    }

    public boolean  link:http://bits.netbeans.org/dev/javadoc/org-openide-text/org/openide/text/ActiveEditorDrop.html#handleTransfer(javax.swing.text.JTextComponent)[handleTransfer(JTextComponent targetComponent]) {
        String body = createBody();
        try {
            HTMLPaletteUtilities.insert(body, targetComponent);
        } catch (BadLocationException ble) {
            return false;
        }
        return true;
    }

}

A red error message remains because you have not created the HTMLPaletteUtilities class yet, which you will do in the next section.

Defining the Insertion

In this section, you create the HTMLPaletteUtilities class, which defines the place where the snippet will be dropped.

  1. Right-click the org.netbeans.modules.newhtmlsnippets node and choose New > Java Class. Type HTMLPaletteUtilities in Class Name, make sure that the org.netbeans.modules.newhtmlsnippets package is selected in the Package drop-down list, and click Finish.

  1. Replace the default content of the HTMLPaletteUtilities.java file with the following:

package org.netbeans.modules.newhtmlsnippets;

import javax.swing.text.BadLocationException;
import javax.swing.text.Caret;
import javax.swing.text.Document;
import javax.swing.text.JTextComponent;
import javax.swing.text.StyledDocument;
import  link:https://bits.netbeans.org/dev/javadoc/org-openide-text/org/openide/text/NbDocument.html[org.openide.text.NbDocument];

public class HTMLPaletteUtilities {

    public static void insert(final String s, final JTextComponent target) throws BadLocationException {

        final StyledDocument doc = (StyledDocument)target.getDocument();

        class AtomicChange implements Runnable {

            @Override
            public void run() {
                Document value = target.getDocument();
                if (value == null)
                    return;
                try {
                    insert(s, target, doc);
                } catch (BadLocationException e) {}
            }
        }

        try {
link:https://bits.netbeans.org/dev/javadoc/org-openide-text/org/openide/text/NbDocument.html#runAtomicAsUser(javax.swing.text.StyledDocument,%20java.lang.Runnable)[NbDocument.runAtomicAsUser(doc, new AtomicChange())];
        } catch (BadLocationException ex) {}

    }

    private static int insert(String s, JTextComponent target, Document doc) throws BadLocationException {

        int start = -1;

        try {

            *//firstly, find selected text range:*
            Caret caret = target.getCaret();
            int p0 = Math.min(caret.getDot(), caret.getMark());
            int p1 = Math.max(caret.getDot(), caret.getMark());
            doc.remove(p0, p1 - p0);

            *//then, replace selected text range with the inserted one:*
            start = caret.getDot();
            doc.insertString(start, s, null);

        } catch (BadLocationException ble) {}

        return start;

    }

}

Declaring and Registering the Code Snippet

Code snippets are registered in two phases. Firstly, you declare a code snippet in an XML file that conforms to the NetBeans Editor Palette Item DTD. In this XML file, you declare your ActiveEditorDrop implementation class, a 16x16 pixel icon, a 32x32 pixel icon, a display name, and a tooltip.

Use the 1.0 version of the DTD if you want the display name and tooltip to be defined in a properties file. Use the 1.1 version of the DTD if you want to declare the display name and tooltip witin the XML file itself. Both approaches are described below.

Secondly, you register the XML file in the layer.xml file, which you will create in this section.

Declaring the Code Snippet

The NetBeans Editor Palette Item DTD is used to declare the ActiveEditorDrop class, the icons, the display name, and the tooltip.

  1. Right-click the org.netbeans.modules.newhtmlsnippets package node and choose New > Other. Select XML Document in the XML folder and click Next. Type BR in File Name. Type \resources at the end of src\org\netbeans\modules\newhtmlsnippets in Folder. Click Next and then click Finish.

  1. Replace the default content of the BR.xml file with the following:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE editor_palette_item PUBLIC "-//NetBeans//Editor Palette Item 1.0//EN"
  "https://netbeans.org/dtds/editor-palette-item-1_0.dtd">

<editor_palette_item version="1.0">

    <class name="org.netbeans.modules.newhtmlsnippets.BR" />

    <icon16 urlvalue="org/netbeans/modules/newhtmlsnippets/resources/BR16.png" />
    <icon32 urlvalue="org/netbeans/modules/newhtmlsnippets/resources/BR32.png" />

    <description localizing-bundle="org.netbeans.modules.newhtmlsnippets.Bundle"
               display-name-key="NAME_html-BR"
               tooltip-key="HINT_html-BR" />

</editor_palette_item>

Instead of the above, you can use the 1.1 DTD, where you can define the display name and tooltip without using a properties file. Below, only the difference with the previous XML file definition is highlighted:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE editor_palette_item PUBLIC "*-//NetBeans//Editor Palette Item 1.1//EN*"
  "https://netbeans.org/dtds/*editor-palette-item-1_1.dtd*">

<editor_palette_item version="1.0">

    <class name="org.netbeans.modules.newhtmlsnippets.BR" />

    <icon16 urlvalue="org/netbeans/modules/newhtmlsnippets/resources/BR16.png" />
    <icon32 urlvalue="org/netbeans/modules/newhtmlsnippets/resources/BR32.png" />

    *<inline-description>
       <display-name>New Line</display-name>
       <tooltip> <![CDATA[ <br>  ]]></tooltip>
    </inline-description>*

</editor_palette_item>
You can choose either of the two approaches above, depending on your requirements.
  1. Add a 16x16 pixel icon and a 32x32 pixel icon to the new resources folder. Name them BR16.png and BR32.png . They can also be in other icon formats, such as GIF or JPG. Make sure that the resource is correctly declared in the BR.xml file. You can right-click them here and then save them to your module’s source structure:

BR32
BR16
  1. If you want to use a properties file for declaring the palette item’s display name and tooltip, which implies that you are using the 1.0 DTD, add the following to the Bundle.properties file:

bundle 60

Registering the Code Snippet

The layer.xml file registers the user interface elements of your module in your application, which in this case is the IDE. Here, we need to register the palette item in the layer.xml file so that the item will appear in the HTML Palette.

  1. Right-click the org.netbeans.modules.newhtmlsnippets package node and choose New > Other. Select Module Development > XML Layer. Click Next and then click Finish.

  1. Add the following tags to the layer.xml file, between the <filesystem> tags:

<folder name="HTMLPalette">
   <folder name="HTML">
      <file name="BR.xml" url="resources/BR.xml">
         <attr name="position" intvalue="150"/>
      </file>
   </folder>
</folder>

Building and Installing the Code Snippet

Now we need to think about installation and distribution. Install and try out the code snippet, by following the steps below.

  1. In the Projects window, right-click the Newhtmlsnippets project and choose Run. The module is built and installed in the target platform. The target platform opens so that you can try out your new module. The default target platform is the installation used by the current instance of the development IDE.

  1. Create a new HTML file in the IDE. When the HTML file opens, it displays the Component Palette (Ctrl-Shift-8) with one additional code snippet, called "New Line", with a tooltip that displays the result of drag-and-dropping the item:

result
  1. Drag the 'New Line' item into the Source Editor and notice that a new <br> tag is inserted at the cursor.

Adding a Customizer

Optionally, you can let a JPanel appear when the palette item is dropped. In the JPanel , you can let the user define values for attributes that relate to the snippet that is about to be created. However, note that adding such a customizer is optional. In the case of a line break, which is what we are creating in this tutorial, there are no attributes that relate to the BR tag. For that reason, to illustrate the customizer functionality, we will add a comment before the BR tag, by means of a customizer.

If you check out the html module from the NetBeans sources, you will find many examples of customizers in the org/netbeans/modules/html/palette/items package.
  1. Add a dependency on the NetBeans Dialogs API .

1. Use the New File dialog (Ctrl-N) to create a JPanel in the org.netbeans.modules.newhtmlsnippets package. Name it BRCustomizer .

  1. Use the Pallette (Ctrl-Shift-8) to drag and drop a JLabel and a JTextField onto the JPanel and arrange the JPanel as follows:

customizer in palette 60
  1. You will need to declare the following at the top of the BRCustomizer class:

private Dialog dialog = null;
private DialogDescriptor descriptor = null;
private boolean dialogOK = false;

private BR br;
private JTextComponent target;
  1. Rewrite the BRCustomizer constructor as follows:

public BRCustomizer(BR br, JTextComponent target) {
    this.br = br;
    this.target = target;

    initComponents();
}
  1. In your BRCustomizer class, add this method, so that, in the next steps, you can open the customizer from your ActiveEditorDrop implementation class:

@NbBundle.Messages({
    "LBL_Customizer_InsertPrefix=Insert",
    "NAME_html-BR=Line Break"})
public boolean showDialog() {
    dialogOK = false;
    descriptor = new DialogDescriptor(this, Bundle.LBL_Customizer_InsertPrefix(), true,
            DialogDescriptor.OK_CANCEL_OPTION, DialogDescriptor.OK_OPTION,
            new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    if (descriptor.getValue().equals(DialogDescriptor.OK_OPTION)) {
                        evaluateInput();
                        dialogOK = true;
                    }
                    dialog.dispose();
                }
            });
    dialog = DialogDisplayer.getDefault().createDialog(descriptor);
    dialog.setVisible(true);
    return dialogOK;
}
  1. Define the evaluateInput() method, which is called in the showDialog() method above, as follows:

private void evaluateInput() {
   String comment = jTextField1.getText();
   br.setComment(comment);
}
  1. Hook your customizer into the ActiveEditorDrop implementation class as follows (only the lines that are changed are highlighted below):

package org.netbeans.modules.newhtmlsnippets;

import javax.swing.text.BadLocationException;
import javax.swing.text.JTextComponent;
import org.netbeans.modules.newhtmlsnippets.HTMLPaletteUtilities;
import  link:https://bits.netbeans.org/dev/javadoc/org-openide-text/org/openide/text/ActiveEditorDrop.html[org.openide.text.ActiveEditorDrop];

public class BR implements  link:https://bits.netbeans.org/dev/javadoc/org-openide-text/org/openide/text/ActiveEditorDrop.html[ActiveEditorDrop] {

    *private String comment = "";*

    public BR() {
    }

    private String createBody() {
        *comment = getComment();
        String Br = "<!-- " + comment + " -->"
                + "\n        <br>";*
        return Br;
    }

    public boolean  link:https://bits.netbeans.org/dev/javadoc/org-openide-text/org/openide/text/ActiveEditorDrop.html#handleTransfer(javax.swing.text.JTextComponent)[handleTransfer(JTextComponent targetComponent]) {

        *BRCustomizer c = new BRCustomizer(this, targetComponent);
        boolean accept = c.showDialog();
        if (accept) {*
            String body = createBody();
            try {
                HTMLPaletteUtilities.insert(body, targetComponent);
            } catch (BadLocationException ble) {
                *accept = false;*
            }
        }
        *return accept;*

    }

    *public String getComment() {
        return comment;
    }

    public void setComment(String comment) {
        this.comment = comment;
    }*

}

Next Steps

For more information about creating and developing NetBeans modules, see the following resources: