HowTo - GCJ: A native Java Compiler

MinGW
MinGW[1] allows you to create native Windows programs. In other words, you can make an exe out of a Java program. The files required for the GCC Java complier are: gcc-java-3.4.2-20040916-1.tar.gz, mingw-runtime-3.9.tar.gz, w32api-3.6.tar.gz, binutils-2.15.91-20040904-1.tar.gz, gcc-core-3.4.2-20040916-1.tar.gz,

These files can be downloaded from the MinGW download page[2] . Additionally, linking requres the libiconv[3] library file libiconv-1.9.1.bin.woe32.zip. This file can be downloaded from its SourceForge.net page[4].

Unzip all the above files in a folder, say D:/mingw. The file gcj.exe will be in D:/mingw/bin. You can add this to the system PATH environment variable.

Compiling a program:
gcj -c -g -O Hello.java

Creating an exe file:
gcj --main=Hello -o Hello Hello.o

This will create a file called Hello.exe

Consider the following program Hello.java
class Hello {
public static void main(String args[]) {
System.out.println("Hello, World!");
}
}


This is a 117 bytes file that will normally require a 15MB JRE from Sun to execute. On the other hand, by using GCJ, the same program compiled into a 3.32MB Hello.exe file.

micro-libgcj
This size can be reduced if we use the minimal micro-libgcj[5] runtime. Note that this runtime supports only the bare minimim features in Java. So, most advanced features including Reflection are not supported.

References
1. http://www.mingw.org/
2. http://www.mingw.org/download.shtml
3. http://www.gnu.org/software/libiconv/
4. http://sourceforge.net/project/showfiles.php?group_id=25167&package_id=51458
5. http://ulibgcj.sourceforge.net/

Simple Java Annotation example

Here we will declare a simple annotation and use it.
* Create the annotation interface first

@Retention(RetentionPolicy.RUNTIME)
@Target (ElementType.FIELD)
@interface CatInfo {
 String name();
 int age();
 double weight();
}

* Create a dummy class to use it: class Cat {}
* Annotate using

@CatInfo(name="Princess", age=2, weight=5.5)
static Cat cat = new Cat();

* Read the annotations using

public CatAnnotator(Cat cat) 
throws SecurityException, NoSuchFieldException {
 Field field = this.getClass().getDeclaredField("cat");
 if( field.isAnnotationPresent(CatInfo.class) ) {
  CatInfo catInfo = 
    (CatInfo)field.getAnnotation(CatInfo.class);
  System.out.println( 
    catInfo.name()+", "+catInfo.age()+", "+catInfo.weight() );
 }
}

* This is the complete source code CatAnnotator.java

Spring Framework (Part 4) - Forms and Validations

In this part we will accept user data from a form, validate it and process it. We continue with Spring Framework (Part 3) - JUnit via XML.
* Copy spring-framework-1.2/dist/spring.tld to the springapp/war/WEB-INF directory
* Make an entry for spring.tld in web.xml
* Modify springapp/src/bus/ProductManager.java to add a new method increasePrice.
* Create springapp/war/WEB-INF/jsp/priceIncrease.jsp
* Create springapp/src/bus/PriceIncrease.java
* Create springapp/src/bus/PriceIncreaseValidator.java
* Create springapp/src/web/PriceIncreaseFormController.java
* Modify springapp/war/WEB-INF/springapp-servlet.xml to define the new form and controller
* Modify springapp/war/WEB-INF/classes/messages.properties to add some messages
* Modify springapp/war/WEB-INF/jsp/hello.jsp to add a url link for price increase
* Compile, deploy and reload the application

References:
Spring Framework (Part 3) - JUnit via XML
http://www.springframework.org/
http://www.springframework.org/docs/MVC-step-by-step/Spring-MVC-step-by-step-Part-3.html

Spring Framework (Part 3) - JUnit via XML

Here we will unit test our spring application from Spring Framework (Part 2) - Display a list of objects. An XML will contain the test data.
* Copy junit.jar to ~\apache-ant-1.6.2\lib
* Modify springapp/build.xml so that it will test all Test*.* classes in the build directory.
* Create springapp/src/tests/TestSpringappController.java
* Create springapp/src/tests/WEB-INF/test-springapp-servlet.xml
* Run 'ant junit' in your project directory which has build.xml

References:
Spring Framework (Part 2) - Display a list of objects
http://www.springframework.org/
http://www.springframework.org/docs/MVC-step-by-step/Spring-MVC-step-by-step-Part-3.html

Spring Framework (Part 2) - Display a list of objects

Here I modify Spring Framework (Part 1) - Hello Spring to display a list of objects.
* Create springapp/src/bus/Product.java and springapp/src/bus/ProductManager.java
*Copy spring-framework-1.2.1/lib/j2ee/jstl.jar, spring-framework-1.2.1/lib/jakarta-taglibs/standard.jar into springapp/war/WEB-INF/lib
* Update springapp/war/WEB-INF/springapp-servlet.xml
* Update >springapp/src/SpringappController.java
* Create springapp/war/WEB-INF/jsp/include.jsp
* Update and move hello.jsp to springapp/war/WEB-INF/jsp/
* Update springapp/war/index.jsp
* Execute ant on the updated build.xml
* Fire your browser to http://localhost:8080/springapp/.
* You should now see the products listed in springapp-servlet.xml
References:
Spring Framework (Part 1) - Hello Spring
http://www.springframework.org/
http://www.springframework.org/docs/MVC-step-by-step/Spring-MVC-step-by-step-Part-2.html

Log4J 1.3 RollingFileAppender

In version 1.3, RollingFileAppender reads configuration from an XML file. We need to read it using JoranConfigurator. This is an sample configuration called traceLogger.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration>

<log4j:configuration xmlns:log4j='http://jakarta.apache.org/log4j/' debug="true">

  <appender name="ROLL" class="org.apache.log4j.rolling.RollingFileAppender">
    <rollingPolicy class="org.apache.log4j.rolling.TimeBasedRollingPolicy">
      <param name="FileNamePattern" value="/trace.%d{yyyy-MM-dd}.log"/>
    </rollingPolicy>      

    <triggeringPolicy class="org.apache.log4j.rolling.SizeBasedTriggeringPolicy">
      <param name="MaxFileSize" value="100000"/>
    </triggeringPolicy>   

    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="%c{1} - %m%n"/>
    </layout>  
  </appender>

  <root>
    <appender-ref ref="ROLL"/>
  </root>

</log4j:configuration>

This is how we could configure it using JoranConfigurator:
new JoranConfigurator().doConfigure("traceLogger.xml", LogManager.getLoggerRepository());

Fixed header in a datagrid

This piece of CSS will let you scroll the contents of you table while keeping the headers fixed.

<style type="text/css" media="screen">
  #container{ border: solid 1px black;width: 50%; height:150px; overflow: auto; }
  .noScroll { position:relative; top:expression(this.offsetParent.scrollTop); 
              background-color:white; font-family: Arial, Helvetica, sans-serif; }
</style>

<div id="container">
  <table border="0" cellpadding="0" cellspacing="0" style="width: 100%">
    <thead>
      <tr class="noScroll">
        <TH>...</TH>
      </tr>
    </thead>
    <tbody>
      <TR><TD>...</TD></TR>
    </tbody>
    </TABLE>
</div>

Reference:http://codebetter.com/blogs/geoff.appleby/archive/2004/10/23/29486.aspx