ant/proposal/sandbox/embed/TaskAdapter.java

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 * information on the Apache Software Foundation, please see
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package org.apache.tools.ant;

import java.lang.reflect.Method;

/**
 * Uses introspection to "adapt" an arbitrary Bean which doesn't
 * itself extend Task, but still contains an execute method and optionally 
 * a setProject method.
 *
 *  The adapter can also be used to wrap tasks that are loaded in a different class loader
 *  by ant, when used in programatic mode.
 *
 * @author Costin Manolache
 */
public class TaskAdapter extends Task {

    /** Object to act as a proxy for. */
    private Object proxy;
    private String methodName="execute";
    Object proxy;
    
    /**
     * Checks whether or not a class is suitable to be adapted by TaskAdapter.
     *
     * This only checks conditions which are additionally required for 
     * tasks adapted by TaskAdapter. Thus, this method should be called by
     * Project.checkTaskClass.
     *
     * Throws a BuildException and logs as Project.MSG_ERR for
     * conditions that will cause the task execution to fail.
     * Logs other suspicious conditions with Project.MSG_WARN.
     * 
     * @param taskClass Class to test for suitability. 
     *                  Must not be <code>null</code>.
     * @param project   Project to log warnings/errors to. 
     *                  Must not be <code>null</code>.
     * 
     * @see Project#checkTaskClass(Class)
     */
    public static void checkTaskClass(final Class taskClass, final Project project) {
        // Any task can be used via adapter. If it doesn't have any execute()
        // method, no problem - it will do nothing, but still get an 'id'
        // and be registered in the project reference table and useable by other
        // tasks.
        
        if( true )
            return;

        // don't have to check for interface, since then
        // taskClass would be abstract too.
        try {
            final Method executeM = taskClass.getMethod( "execute", null );
            // don't have to check for public, since
            // getMethod finds public method only.
            // don't have to check for abstract, since then
            // taskClass would be abstract too.
            if(!Void.TYPE.equals(executeM.getReturnType())) {
                final String message =
                    "return type of execute() should be void but was \""+
                    executeM.getReturnType()+"\" in " + taskClass;
                project.log(message, Project.MSG_WARN);
            }
        } catch(NoSuchMethodException e) {
            final String message = "No public execute() in " + taskClass;
            project.log(message, Project.MSG_ERR);
            throw new BuildException(message);
        }
    }

    private IntrospectionHelper ih;

    void setIntrospectionHelper( IntrospectionHelper ih ) {
        this.ih=ih;
    }

    IntrospectionHelper getIntrospectionHelper() {
        if( ih==null ) {
            ih = IntrospectionHelper.getHelper(target.getClass());
        }
        return ih;
    }
    
    /** Experimental, non-public method for better 'adaptation'
     *
     */
    void setAttribute( String name, String value )
        throws BuildException
    {
        try {
            ih.setAttribute( project, proxy, name, value );
        } catch( BuildException ex ) {
            if( "do".equals( name ) ) {
                setDo( value );
            } else {
                throw ex;
            }
        }
    }
        
    /** Set the 'action' method. This allow beans implementing multiple
     * actions or using methods other than 'execute()' to be used in ant
     * without any modification.
     * 
     *  @ant:experimental 
     */
    public void setDo(String methodName ) {
        this.methodName=methodName;
    }
    
    /**
     * Executes the proxied task.
     */
    public void execute() throws BuildException {
        Method setProjectM = null;
        try {
            Class c = proxy.getClass();
            setProjectM = 
                c.getMethod( "setProject", new Class[] {Project.class});
            if(setProjectM != null) {
                setProjectM.invoke(proxy, new Object[] {project});
            }
        } catch (NoSuchMethodException e) {
            // ignore this if the class being used as a task does not have
            // a set project method.
        } catch( Exception ex ) {
            log("Error setting project in " + proxy.getClass(), 
                Project.MSG_ERR);
            throw new BuildException( ex );
        }


        Method executeM=null;
        try {
            Class c=proxy.getClass();
            executeM=c.getMethod( methodName, new Class[0] );
            if( executeM == null ) {
                log("No public " + methodName + "() in " + proxy.getClass(), Project.MSG_ERR);
                throw new BuildException("No public " + methodName +"() in " + proxy.getClass());
            }
            executeM.invoke(proxy, null);
            return; 
        } catch (java.lang.reflect.InvocationTargetException ie) {
            log("Error in " + proxy.getClass(), Project.MSG_ERR);
            Throwable t = ie.getTargetException();
            if (t instanceof BuildException) {
                throw ((BuildException) t);
            } else {
                throw new BuildException(t);
            }
        } catch( Exception ex ) {
            log("Error in " + proxy.getClass(), Project.MSG_ERR);
            throw new BuildException( ex );
        }

    }
    
    /**
     * Sets the target object to proxy for.
     * 
     * @param o The target object. Must not be <code>null</code>.
     */
    public void setProxy(Object o) {
        this.proxy = o;
    }

    /**
     * Returns the target object being proxied.
     * 
     * @return the target proxy object
     */
    public Object getProxy() {
        return this.proxy ;
    }

}