Quick Introduction To Echo
A Java Thin Client Framework Note: The material here was used in a presentation about Echo for the Cincinnati Java User Group on 2005.05.16.
Echo For Managers- A Java framework for creating web-based applications.
- Works with browsers supporting JavaScript >= 1.3, e.g. IE, FireFox, Netscape, ...
- No client side binaries, ActiveX, Plugins, ...
- No server side special server. A program is deployed as a servlet to a servlet container e.g. Tomcat.
- Open source with LGPL and Mozilla Public License. Support available for $.
- Released in 2003.
- Currently on version 1.1.4, with version 2.0 in Alpha.
Echo For Geeks - The front end is written completely in Java; as a programmer you do not write HTML, JavaScript, JSP, XML, XSL, CRAP, ...
- Echo provides a component library similar to Swing for writing the front end.
- At run-time, the components generate the appropriate HTML and JavaScript for the browser.
- An Eclipse plugin is available for GUI design but it costs $350/License.
- You need to import and deploy two jar files with total size about 360KB.
- Works with JDK 1.2 and higher, Servlet Specs 2.2 or higher.
- Main developer Tod Liebeck.
- If you are familiar with Swing, you need 10 to 20 hours to become productive.
- Good introduction tutorial and JavaDocs, but no good documents on how to write big apps. However, it is not hard to figure out.
- Version 2 will use AJAX (Asynchronous JavaScript and XML). Updating a component on the page instead of whole page. Google map and GMail use AJAX.
An example application (written with Echo 1.1.4) source and binaries are here. (7.15 MB) Links
- Distributed by www.nextapp.com
- Main Page: www.nextapp.com/products/echo
- Tutorial: www.nextapp.com/products/echo/doc/tutorial/
- EchoPoint, a library of Echo web components: echopoint.sourceforge.net
Test Code
package com.tek271.test;
import nextapp.echo.*;
import nextapp.echo.event.*;
import nextapp.echoservlet.EchoServer;
public class HelloServlet extends EchoServer {
// EchoServer extends javax.servlet.http.HttpServlet
public EchoInstance newInstance() {
//return new HelloWorld();
//***** Demo step 5: buttons and handlers
return new ButtonsTest();
}
class HelloWorld extends EchoInstance {
// Declare the init() method which is abstract in EchoInstance
public Window init() {
Window w= new Window("Hello World title");
ContentPane contentPane= new ContentPane();
w.setContent(contentPane);
Label lbl= new Label("Hello World");
contentPane.add(lbl);
// ***** Demo step 1: font and color
lbl.setFont( new Font(Font.VERDANA, Font.BOLD, 16) );
lbl.setForeground(Color.BLUE);
// ***** Demo step 2: image
HttpImageReference img= new HttpImageReference("file://C:/util/graphics/animated/horse.gif");
lbl.setIcon(img);
// ***** Demo step 3: text field
contentPane.add( Filler.createVerticalStrut(20) ); // make vertical space
TextField tf= new TextField("default value");
contentPane.add(tf);
// ***** Demo step 4: style
Style style= new Style();
style.setAttribute(TextField.STYLE_BACKGROUND, Color.YELLOW);
style.setAttribute(TextField.STYLE_FOREGROUND, Color.BLUE );
style.setAttribute(TextField.STYLE_FONT, new Font(Font.ARIAL, Font.BOLD, 14) );
style.setAttribute(TextField.STYLE_BORDER_SIZE, 4);
style.setAttribute(TextField.STYLE_BORDER_COLOR, Color.RED);
style.setImmutable(); // throw exception if style changed
tf.applyStyle(style); // apply style on text field
return w;
}
} // class HelloWorld
class ButtonsTest extends EchoInstance implements ActionListener {
private Button pRed, pGreen, pBlue, pWhite;
private ContentPane pContent;
public void actionPerformed(ActionEvent e) {
Object src= e.getSource();
if (src == pRed) pContent.setBackground(Color.RED);
else if (src == pGreen) pContent.setBackground(Color.GREEN);
else if (src == pBlue) pContent.setBackground(Color.BLUE);
else if (src == pWhite) pContent.setBackground(Color.WHITE);
} // actoinPerformed();
public Window init() {
Window window=new Window("Button Demo");
pContent=new ContentPane();
window.setContent(pContent);
Label label=new Label("Click on a button to change the background:");
pContent.add(label);
pRed= createButton("Red", Color.RED);
pGreen= createButton("Green", Color.GREEN);
pBlue= createButton("Blue", Color.BLUE);
pWhite= createButton("White", Color.WHITE);
return window;
}
private Button createButton(String aCaption, Color aBackground) {
Button r= new Button(aCaption);
r.setBackground(aBackground);
r.addActionListener(ButtonsTest.this);
r.setToolTipText("Change the background color to " + aCaption);
pContent.add(r);
return r;
}
} // class ButtonsTest
} // class HelloServlet
|
| | |
|
|