{Complexity} » Java

Spring MVC + Tiles

admin — Mon, 14 Dec 2009 02:14:54 +0000

1. create web.xml
action org.springframework.web.servlet.DispatcherServlet 1 action *.do

2. create action-servlet.xml


  

    

    
  

	

    
  

    

      med

    

    

      userMain

    

  
  

  

    

  
  

	

	  

	    

	      /WEB-INF/UrlMap.properties

	    

	  

    

  
  

    

      

        /WEB-INF/tiles-def.xml

3. create TestController
package com.bluewiseinc.erp.common.web; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.springframework.web.servlet.ModelAndView; import org.springframework.web.servlet.mvc.multiaction.MultiActionController;

public class TestController extends MultiActionController { public ModelAndView testMain(HttpServletRequest request, HttpServletResponse response) throws Exception { return new ModelAndView("test/test_main", "testMain", null); } }

4. UrlMap.properties
## test module mapping /test/index.do=testController

5. tiles-def.xml
"-//Apache Software Foundation//DTD Tiles Configuration 2.0//EN" "http://tiles.apache.org/dtds/tiles-config_2_0.dtd">

6. message.properties
# Page titles index.title=Test Spring MVC + Tiles

7. default.jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %> <%@ taglib prefix="fmt" uri="http://java.sun.com/jstl/fmt" %> <%@ taglib prefix="tiles" uri="http://tiles.apache.org/tags-tiles" %> <%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%> <fmt:message key="index.title"/>

SwingWorker not on Java 6.0

admin — Thu, 24 Apr 2008 14:15:08 +0000

SwingWorker is useful when a time-consuming task has to be performed following a user-interaction event (for example, parsing a huge XML File, on pressing a Button). The most straightforward way to do it is :

[sourcecode language='java']
private Document doc;
…
JButton button = new JButton(“Open XML”);
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
doc = loadXML();
}
});
[/sourcecode]

This will work, but unfortunately, the loadXML() method will be called in the same thread as the main Swing thread, so if the method needs time to perform, the GUI will freeze during this time.

[sourcecode language='java']
package com.wsjoung.demo;
import javax.swing.SwingUtilities;

public abstract class SwingWorker {
// see getValue(), setValue()
private Object value;
private Thread thread;

private static class ThreadVar {
private Thread thread;
ThreadVar(Thread t) { thread = t; }
synchronized Thread get() { return thread; }
synchronized void clear() { thread = null; }
}

private ThreadVar threadVar;

protected synchronized Object getValue() {
return value;
}

private synchronized void setValue(Object x) {
value = x;
}

public abstract Object construct();

public void finished() {
}

public void interrupt() {
Thread t = threadVar.get();
if (t != null) {
t.interrupt();
}
threadVar.clear();
}

public Object get() {
while (true) {
Thread t = threadVar.get();
if (t == null) {
return getValue();
}
try {
t.join();
}
catch (InterruptedException e) {
// propagate
Thread.currentThread().interrupt();
return null;
}
}
}

public SwingWorker() {
final Runnable doFinished = new Runnable() {
public void run() { finished(); }
};

Runnable doConstruct = new Runnable() {
public void run() {
try {
setValue(construct());
}
finally {
threadVar.clear();
}

SwingUtilities.invokeLater(doFinished);
}
};

Thread t = new Thread(doConstruct);
threadVar = new ThreadVar(t);
t.start();
}
}
[/sourcecode]

SwingWorker.java

[sourcecode language='java']
public class Task{
public void go() {
current = 0;
final SwingWorker worker = new SwingWorker() {
public Object construct() {
return new ActualTask();
}
};
}

class ActualTask {
ActualTask() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {}
}
}
}
[/sourcecode]

Task.java

what's static?

admin — Mon, 14 Apr 2008 19:31:25 +0000

First of all, the meaning of static in java is embedded or belong to a specific class not to its instance, and therefore there is no such static class.

There is no such static class
Embedded or belong to a specific class
Global variable
No need to load and create its instance

Most of methods and variables in Math class are static, because those are not need to be instanced in most of cases. we just use return value of PI or max(int a, int b).

class Bicycle {

private static int numberOfBicycles = 0;
private int id;

public Bicycle() {
id = ++numberOfBicycles;
}

public static int getNumberOfBicycles() {
return numberOfBicycles;
}
public int getID() {
return id;
}

public static void main(String[] args) {
Bicycle b1 = new Bicycle();
Bicycle b2 = new Bicycle();

System.out.println(“static result : “+getNumberOfBicycles());
System.out.println(“static result : “+numberOfBicycles);
System.out.println(“instance result : “+b1.getID());
System.out.println(“instance result : “+b2.getID());
}
}

Another characteristic of static is that even if we create instance of a class, jvm does not create instance variables for static resources. in above source code, there is no difference calling b1.getNumberOfBicycles(), b2.getNumberOfBicycles() and just getNumberOfBicycles() or directly numberOfBicycles
that mean we should call static variable with its class name because it’s belong to it. just like Bicycle.numberOfBicycles or in this example, getNumberOfBicycles() because we have a getter.
otherwise get confused.

DataSource setup on Tomcat

admin — Fri, 21 Sep 2007 20:38:24 +0000

1. create META-INF/context.xml

source=”org.eclipse.jst.j2ee.server:e-sports”>
prefix=”e-sports_log.” suffix=”.txt” timestamp=”true” />
auth=”Container”
type=”javax.sql.DataSource”
driverClassName=”oracle.jdbc.driver.OracleDriver”
factory=”org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory”
url=”jdbc:oracle:thin:@127.0.0.1:1521:ORA92″
username=”scott”
password=”tiger”
maxActive=”20″
maxIdle=”10″
maxWait=”-1″ />

2. test.jsp
<%@ page import=”java.sql.Connection” %>
<%@ page import=”java.sql.ResultSet” %>
<%@ page import=”java.sql.SQLException” %>
<%@ page import=”java.sql.Statement” %>
<%@ page import=”javax.naming.Context” %>
<%@ page import=”javax.naming.InitialContext” %>
<%@ page import=”javax.naming.NamingException” %>
<%@ page import=”javax.sql.DataSource” %>

<%
Context ctx = null;
DataSource source = null;
Connection con = null;

try {
ctx = new InitialContext();
ctx = (Context) ctx.lookup(“java:comp/env”);
source = (DataSource) ctx.lookup(“jdbc/myoracle”);

System.out.println(“DataSource ===========================”+ source);

con = source.getConnection();
System.out.println(“Connection ============================”+ con);
} catch (NamingException ne) {
ne.printStackTrace();
}
%>

Signed java applet

admin — Tue, 15 May 2007 17:43:00 +0000

Applet Security Basics

Below are the basic facts regarding applet security and Java Plug-in. More detail can be found in the next chapter, How RSA Signed Applet Verification Works in Java Plug-in.

All unsigned applets are run under the standard applet security model.
If usePolicy IS NOT DEFINED in the java.policy file, then a signed applet has the AllPermission permission if:
Java Plug-in can verify the signers, and the user, when prompted, agrees to granting the AllPermission permission.
If usePolicy IS DEFINED, then a signed applet has only the permissions defined in java.policy and no prompting occurs.

Moreover, note that Java Plug-in now handles certificate management; i.e., the certificate verification task is no longer passed off to the browser.

keytool -genkey -keyalg rsa -alias MyCert
keytool -certreq -alias MyCert
keytool -import -alias MyCert -file VSSStanleyNew.cer

keytool -selfcert

and

jarsigner AppletName.jar MyCert
jarsigner -verify -verbose -certs AppletName.jar

Java Plugin guide

Eclipse web.xml validation problem

admin — Wed, 07 Feb 2007 02:43:14 +0000

The problem is because of “http://java.sun.com/xml/ns/j2ee/j2ee_1_4.xsd” fil, it points ibm’s schema instead of Sun’s

Window -> Preferences… -> Web and XML -> XML Catalog

URI : http://java.sun.com/xml/ns/j2ee/j2ee_web_services_client_1_1.xsd
Key Type : Schema Location
Key : http://www.ibm.com/webservices/xsd/j2ee_web_services_client_1_1.xsd

Thanks Carey Evans

Java SE 6 Key Features

admin — Wed, 13 Dec 2006 06:54:12 +0000

New Security Features and Enhancements

Native platform Security (GSS/Kerberos) integration.
Java Authentication and Authorization Service (JAAS) login module that employs LDAP authentication
New Smart Card I/O API
» Find out more

Integrated Web Services

New API for XML digital signature services for secure web services
New Client and Core Java Architecture for XML-Web Services (JAX-WS) 2.0 APIs
New support for Java Architecture for XML Binding (JAXB) 2.0
» Find out more

Scripting Language Support (JSR 223)

New framework and API for scripting languages
Mozilla Rhino engine for JavaScript built into the platform
» Find out more

Enhanced Management and Serviceability

Improved JMX Monitoring API
Runtime Support for dTrace (Solaris 10 and future Solaris OS releases only)
Improved memory usage analysis and leak detection
» Find out more

Increased Developer Productivity

JDBC 4.0 support (JSR 221)
Significant library improvements
Improvements to the Java Platform Debug Architecture (JPDA) & JVM Tool Interface

Improved User Experience

look-and-feel updates to better match underlying operating system
Improved desktop performance and integration
Enhanced internationalization support

String constant pool

admin — Sun, 26 Nov 2006 23:50:05 +0000

Everybody knows about String constant pool which is for efficient memory management in java. Basically most of objects are managed on heap area but String object. In most of ordinary application, programmers use String object quite often and this String object quite frequently need to be changed or it occupies large amounts of memory. Therefore instead of managing String object on heap area, they introduced String constant pool.

One of important characteristic of String constant pool is that it doesn’t create same String object if there is already String constant in the pool.

String var1 = “This is String Literal”; String var2 = “This is String Literal”;

For above two String objects, JVM creates only one object in the String constant pool and for the second string reference variable (var2), it points the string object which is created for var1. In this case, (var1 == var2) is true.

But one thing, people make confused is that. It works only when it encounter on String Literal with double quote.

String var3 = new String(“This is String Literal”);

In this case, a regular object will be created by new keyword on heap area and it will be placed in the String constant pool. Finally it will be assigned to the reference variable, var3. This process is just by passing from String constant pool management. Therefore, (var1 == var3) is false.

"null", is this Object or not?

admin — Sun, 26 Nov 2006 08:15:44 +0000

In java, some people say null is Object and they also use “null object” term when they try to explain something related in null like NullPointerException.

And some people simply show “null instanceof Object” result to prove that null is not Object. Of course it returns false for “null instanceof Object”. Because null is technically not Object.

The reason why people keep regarding null as a kind of Object is that they are confused those two terms, Object itself and Reference variable which points an object. Whenever they say “null object”, which means actually reference variable, and that reference variable assigned for a specific bit pattern which is for null.

Read all files in a directory

admin — Fri, 17 Nov 2006 01:09:43 +0000

int fileCount = 0;
File dir = new File(inputDirName);
File[] strFilesDirs = dir.listFiles();

if (strFilesDirs == null) {
System.err.println(inputDirName +” is not valid directory name or there is no pdb file”);
System.exit(1);
}
for (int i=0; i
if (strFilesDirs[i].isDirectory()) {
//System.out.println(“Directory: “+strFilesDirs[i]);
} else if (strFilesDirs[i].isFile()) {
//System.out.println(“File: “+strFilesDirs[i]+”(“+strFilesDirs[i].length()+”)”);
fileCount = fileCount + 1;
}
}

beside, there is no such method which is changing directory.