Generating Java code from XML in Eclipse

Question

I am working on a project that will have several Java classes that are very similar to each other, and that I would like to generate from XML files. What I would like to be able to do is change the Eclipse build process to do something like this:

• Compile the code generator
• Run the code generator, converting the XML to Java
• Compile the rest of the project

I could do this all manually but I would prefer to be able to have Eclipse do it all for me.

Example

I want to be able to take a source XML file that looks like this:

<command-list>
    <command name="DATE" />
    <command name="GROUP">
        <capability "READER" />
        <argument "groupname" />
    </command>
    <command name="ARTICLE">
        <capability "READER" />
        <argument "message-id" optional="true" />
    </command>
</command-list>

and have it give me something similar to the following (in separate files as appropriate):

public class Date extends Command {
    public ResponseCode execute() {
        Server srv = getServer();
        srv.send("DATE");
        return srv.getResponse();
    }
}

public class Group extends Command {
    public ResponseCode execute() {
        Server srv = getServer();
        if (srv.hasCapability(Capabilities.READER) == false) {
            Log.debug("Attempting non-available capability: READER");
        }
        String groupname = getArgument("groupname");
        if (groupname == null) {
             throw new InvalidArgumentException("Require groupname");
        }
        String command = "GROUP";
        if (groupname != null) command += " " + groupname;
        srv.send(command);
        return srv.getResponse();
    }
}

public class Article extends Command {
    public ResponseCode execute() {
        Server srv = getServer();
        if (srv.hasCapability(Capabilities.READER) == false) {
            Log.debug("Attempting non-available capability: READER");
        }
        String messageId = getArgument("messageId");
        String command = "ARTICLE";
        if (messageId != null) command += " " + messageId;
        srv.send(command);
        return srv.getResponse();
    }
}

Answer 1

This is exactly what the JET component in the Model to Text (M2T) project was made for. In fact, you can even create the project, .classpath and any other files you need with JET.

Jet templates are as follows. Note that these templates must be named exactly as shown.

/templates/main.jet

<%@taglib prefix="ws" id="org.eclipse.jet.workspaceTags" %>
<%-- Main entry point for com.lacqui.command.xform --%>

<%-- 
  Let c:iterate tags set the XPath context object.
  For 100% compatibility with JET 0.9.x or earlier, remove this statement
 --%>
<c:setVariable var="org.eclipse.jet.taglib.control.iterateSetsContext" select="true()"/>

    <c:setVariable select="/command-list" var="command-list" />

    --- traverse input model, performing calculations and storing 
    --- the results as model annotations via c:set tag 

    <c:set select="$command-list" name="project">com.lacqui.commands</c:set>
    <c:set select="$command-list" name="commandPkg">com.lacqui.commands</c:set>
    <c:set select="$command-list" name="commandDir"><c:get select="translate($command-list/@commandPkg,'.','/')" /></c:set>

    <c:iterate select="$command-list/command" var="command" >

            - Derive the class name from the name of the command

        <c:set select="$command" name="classname"><c:get select="camelCase($command/@name)" />Command</c:set>

        <c:iterate select="$command/argument" var="argument">

            <c:if test="not($argument/@optional)">
                <c:set select="$argument" name="optional">false</c:set>
            </c:if>

        </c:iterate>

    </c:iterate>

   --- traverse annotated model, performing text generation actions 
   --- such as ws:file, ws:folder and ws:project 

   <ws:project name="{$command-list/@project}" />
   <ws:file template="templates/project.jet" path="{$command-list/@project}/.project"  />
   <ws:file template="templates/classpath.jet" path="{$command-list/@project}/.classpath"/>

    <c:iterate select="$command-list/command" var="command" >

        <ws:file template="templates/class.jet" path="{$command-list/@project}/src/{$command-list/@commandDir}/{$command/@classname}.java" replace="true"/>

    </c:iterate>

/templates/classpath.jet

<?xml version="1.0" encoding="UTF-8"?>
<classpath>
    <classpathentry kind="src" path="src"/>
    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
    <classpathentry kind="output" path="bin"/>
</classpath>

/templates/project.jet

<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
    <name><c:get select="$command-list/@project" /></name>
    <comment></comment>
    <projects>
    </projects>
    <buildSpec>
        <buildCommand>
            <name>org.eclipse.jdt.core.javabuilder</name>
            <arguments>
            </arguments>
        </buildCommand>
    </buildSpec>
    <natures>
        <nature>org.eclipse.jdt.core.javanature</nature>
    </natures>
</projectDescription>

/templates/class.jet

package <c:get select="$command-list/@commandPkg" />;

public class <c:get select="$command/@classname" /> extends Command {
    public ResponseCode execute() {
        Server srv = getServer();
<c:iterate select="$command/capability" var="capability">

        if (srv.hasCapability(Capabilities.<c:get select="$capability/@name"/>) == false) {
            Log.debug("Attempting non-available capability: <c:get select="$capability/@name"/>");
        }
</c:iterate>        
<c:iterate select="$command/argument" var="argument">

        String <c:get select="$argument/@name"/> = getArgument("<c:get select="$argument/@name"/>");
<c:if test="$argument/@optional = 'false'" >
        if (<c:get select="$argument/@name"/> == null) {
             throw new InvalidArgumentException("Require <c:get select="$argument/@name"/>");
        }
</c:if>
</c:iterate>        

        String command = "GROUP";
<c:iterate select="$command/argument" var="argument">
        if (<c:get select="$argument/@name"/> != null) command += " -<c:get select="$argument/@name"/> " + <c:get select="$argument/@name"/>;
</c:iterate>       

        srv.send(command);
        return srv.getResponse();
    }
}

and using this model:

<command-list>
    <command name="DATE" />
    <command name="GROUP">
        <capability name="LOGGER" />
        <capability name="AUTHENTICATOR" />
        <argument name="groupname" />
    </command>
    <command name="ARTICLE">
        <capability name="READER" />
        <argument name="article-id" optional="false" />
        <argument name="message-id" optional="true" />
    </command>
</command-list>

gives a complete java project named com.lacqui.commands containing three java files:

package com.lacqui.commands;

public class ArticleCommand extends Command {
    public ResponseCode execute() {
        Server srv = getServer();

        if (srv.hasCapability(Capabilities.READER) == false) {
            Log.debug("Attempting non-available capability: READER");
        }

        String article-id = getArgument("article-id");
        if (article-id == null) {
             throw new InvalidArgumentException("Require article-id");
        }

        String message-id = getArgument("message-id");

        String command = "GROUP";
        if (article-id != null) command += " -article-id " + article-id;
        if (message-id != null) command += " -message-id " + message-id;

        srv.send(command);
        return srv.getResponse();
    }
}

and this:

package com.lacqui.commands;

public class GroupCommand extends Command {
    public ResponseCode execute() {
        Server srv = getServer();

        if (srv.hasCapability(Capabilities.LOGGER) == false) {
            Log.debug("Attempting non-available capability: LOGGER");
        }

        if (srv.hasCapability(Capabilities.AUTHENTICATOR) == false) {
            Log.debug("Attempting non-available capability: AUTHENTICATOR");
        }

        String groupname = getArgument("groupname");
        if (groupname == null) {
             throw new InvalidArgumentException("Require groupname");
        }

        String command = "GROUP";
        if (groupname != null) command += " -groupname " + groupname;

        srv.send(command);
        return srv.getResponse();
    }
}

Answer 2

You might want to take a look at JaxB.

Lars Vogel did a simple tutorial if you want to take a quick look at it.
JAXB Tutorial

Also here is a benchmark test of xml unmarshaling.
XML unmarshalling benchmark in Java: JAXB vs STax vs Woodstox