simple Ant ProjectHelper that reads "buildfile from File"

InMemoryProjectHelper

Created in response to a question on the Ant user list "[Ant]Read buid.xml file in memory" - http://marc.info/?t=142367261300007&r=1&w=2

Run with something like

ANT_OPTS='-Dorg.apache.tools.ant.ProjectHelper=org.example.InMemoryProjectHelper' ant -lib .  -f "arbitrary file"

this isn't anything I'd use myself, just proving how it can be done.

InMemoryProjectHelper.java

package org.example;

import java.io.File;
import java.io.InputStream;
import java.io.StringBufferInputStream;
import java.net.URL;
import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.helper.AntXMLContext;
import org.apache.tools.ant.helper.ProjectHelper2;
import org.apache.tools.ant.util.FileUtils;
import org.apache.tools.ant.util.JAXPUtils;
import org.xml.sax.InputSource;
import org.xml.sax.XMLReader;

public class InMemoryProjectHelper extends ProjectHelper2 {

    @Override
    public void parse(Project project, Object source, RootHandler handler) throws BuildException {
        if (!(source instanceof File)) {
            // invoked to parse Ant's internal antlibs
            super.parse(project, source, handler);

        } else {
        
            // source is the "real" build file that would need to be decrypted or whatever
            // the code below just shows how to use a different stream
            InputStream inputStream = null;
            try {
                inputStream = new StringBufferInputStream("<project><echo>Called!</echo></project>");
                InputSource inputSource = new InputSource(inputStream);
                XMLReader parser = JAXPUtils.getNamespaceXMLReader();

                // this is required for the ProjectHelper2 machinery to work
                AntXMLContext context = (AntXMLContext) project.getReference("ant.parsing.context");
                context.setBuildFile((File) source);

                parser.setContentHandler(handler);
                parser.setEntityResolver(handler);
                parser.setErrorHandler(handler);
                parser.setDTDHandler(handler);
                parser.parse(inputSource);
            } catch (Exception ex) {
                throw new BuildException(ex);
            } finally {
                FileUtils.close(inputStream);
            }
        }
    }

}