src/java/org/apache/velocity/runtime/parser/node/ASTMethod.java

package org.apache.velocity.runtime.parser.node;

/*
 * Copyright 2000-2006 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License")
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.lang.reflect.InvocationTargetException;

import org.apache.commons.lang.ArrayUtils;
import org.apache.commons.lang.StringUtils;
import org.apache.velocity.app.event.EventHandlerUtil;
import org.apache.velocity.context.InternalContextAdapter;
import org.apache.velocity.exception.MethodInvocationException;
import org.apache.velocity.runtime.parser.Parser;
import org.apache.velocity.runtime.parser.ParserVisitor;
import org.apache.velocity.util.introspection.Info;
import org.apache.velocity.util.introspection.IntrospectionCacheData;
import org.apache.velocity.util.introspection.VelMethod;

/**
 *  ASTMethod.java
 *
 *  Method support for references :  $foo.method()
 *
 *  NOTE :
 *
 *  introspection is now done at render time.
 *
 *  Please look at the Parser.jjt file which is
 *  what controls the generation of this class.
 *
 * @author <a href="mailto:jvanzyl@apache.org">Jason van Zyl</a>
 * @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
 * @version $Id$
 */
public class ASTMethod extends SimpleNode
{
    private String methodName = "";
    private int paramCount = 0;

    /**
     * @param id
     */
    public ASTMethod(int id)
    {
        super(id);
    }

    /**
     * @param p
     * @param id
     */
    public ASTMethod(Parser p, int id)
    {
        super(p, id);
    }

    /**
     * @see org.apache.velocity.runtime.parser.node.SimpleNode#jjtAccept(org.apache.velocity.runtime.parser.ParserVisitor, java.lang.Object)
     */
    public Object jjtAccept(ParserVisitor visitor, Object data)
    {
        return visitor.visit(this, data);
    }

    /**
     *  simple init - init our subtree and get what we can from
     *  the AST
     * @param context
     * @param data
     * @return The init result
     * @throws Exception
     */
    public Object init(  InternalContextAdapter context, Object data)
        throws Exception
    {
        super.init(  context, data );

        /*
         *  this is about all we can do
         */

        methodName = getFirstToken().image;
        paramCount = jjtGetNumChildren() - 1;

        return data;
    }

    /**
     *  invokes the method.  Returns null if a problem, the
     *  actual return if the method returns something, or
     *  an empty string "" if the method returns void
     * @param o
     * @param context
     * @return Result or null.
     * @throws MethodInvocationException
     */
    public Object execute(Object o, InternalContextAdapter context)
        throws MethodInvocationException
    {
        /*
         *  new strategy (strategery!) for introspection. Since we want
         *  to be thread- as well as context-safe, we *must* do it now,
         *  at execution time.  There can be no in-node caching,
         *  but if we are careful, we can do it in the context.
         */

        VelMethod method = null;

        Object [] params = new Object[paramCount];

        try
        {
            /*
             * sadly, we do need recalc the values of the args, as this can
             * change from visit to visit
             */

            final Class[] paramClasses = paramCount > 0 ? new Class[paramCount] : ArrayUtils.EMPTY_CLASS_ARRAY;

            for (int j = 0; j < paramCount; j++)
            {
                params[j] = jjtGetChild(j + 1).value(context);

                if (params[j] != null)
                {
                    paramClasses[j] = params[j].getClass();
                }
            }

            /*
             *   check the cache
             */

            MethodCacheKey mck = new MethodCacheKey(methodName, paramClasses);
            IntrospectionCacheData icd =  context.icacheGet( mck );

            /*
             *  like ASTIdentifier, if we have cache information, and the
             *  Class of Object o is the same as that in the cache, we are
             *  safe.
             */

            if ( icd != null && (o != null && icd.contextData == o.getClass()) )
            {

                /*
                 * get the method from the cache
                 */

                method = (VelMethod) icd.thingy;
            }
            else
            {
                /*
                 *  otherwise, do the introspection, and then
                 *  cache it
                 */

                for (int j = 0; j < paramCount; j++)
                    params[j] = jjtGetChild(j + 1).value(context);

                method = rsvc.getUberspect().getMethod(o, methodName, params, new Info(context.getCurrentTemplateName(), getLine(), getColumn()));

                if ((method != null) && (o != null))
                {
                    icd = new IntrospectionCacheData();
                    icd.contextData = o.getClass();
                    icd.thingy = method;

                    context.icachePut( mck, icd );
                }
            }

            /*
             *  if we still haven't gotten the method, either we are calling
             *  a method that doesn't exist (which is fine...)  or I screwed
             *  it up.
             */

            if (method == null)
                return null;
        }
        catch( MethodInvocationException mie )
        {
            /*
             *  this can come from the doIntrospection(), as the arg values
             *  are evaluated to find the right method signature.  We just
             *  want to propogate it here, not do anything fancy
             */

            throw mie;
        }
        /**
         * pass through application level runtime exceptions
         */
        catch( RuntimeException e )
        {
            throw e;
        }
        catch( Exception e )
        {
            /*
             *  can come from the doIntropection() also, from Introspector
             */

            log.error("ASTMethod.execute() : exception from introspection", e);
            return null;
        }

        try
        {
            /*
             *  get the returned object.  It may be null, and that is
             *  valid for something declared with a void return type.
             *  Since the caller is expecting something to be returned,
             *  as long as things are peachy, we can return an empty
             *  String so ASTReference() correctly figures out that
             *  all is well.
             */

            Object obj = method.invoke(o, params);

            if (obj == null)
            {
                if( method.getReturnType() == Void.TYPE)
                {
                    return "";
                }
            }

            return obj;
        }
        catch( InvocationTargetException ite )
        {
            /*
             *  In the event that the invocation of the method
             *  itself throws an exception, we want to catch that
             *  wrap it, and throw.  We don't log here as we want to figure
             *  out which reference threw the exception, so do that
             *  above
             */

            /*
             *  let non-Exception Throwables go...
             */

            Throwable t = ite.getTargetException();
            if (t instanceof Exception)
            {
                try
                {
                    return EventHandlerUtil.methodException( rsvc, context, o.getClass(), methodName, (Exception) t );
                }

                /**
                 * If the event handler throws an exception, then wrap it
                 * in a MethodInvocationException.  Don't pass through RuntimeExceptions like other
                 * similar catchall code blocks.
                 */
                catch( Exception e )
                {
                    throw new MethodInvocationException(
                        "Invocation of method '"
                        + methodName + "' in  " + o.getClass()
                        + " in template " + context.getCurrentTemplateName()
                        + " at line=" + this.getLine() + " column=" + this.getColumn()
                        + " threw exception "
                        + e.getClass() + " : " + e.getMessage(),
                        e, methodName );
                }
            }
            else
            {
                /*
                 * no event cartridge to override. Just throw
                 */

                throw new MethodInvocationException(
                "Invocation of method '"
                + methodName + "' in  " + o.getClass()
                + " in template " + context.getCurrentTemplateName()
                + " at line=" + this.getLine() + " column=" + this.getColumn()
                + " threw exception "
                + ite.getTargetException().getClass() + " : "
                + ite.getTargetException().getMessage(),
                ite.getTargetException(), methodName );
            }
        }
        /**
         * pass through application level runtime exceptions
         */
        catch( RuntimeException e )
        {
            throw e;
        }
        catch( Exception e )
        {
            log.error("ASTMethod.execute() : exception invoking method '"
                      + methodName + "' in " + o.getClass(), e);
            return null;
        }
    }

    /**
     * Internal class used as key for method cache.  Combines
     * ASTMethod fields with array of parameter classes.  Has
     * public access (and complete constructor) for unit test 
     * purposes.
     */
    public class MethodCacheKey
    {
        private final String methodName;  
        private final Class[] params;

        public MethodCacheKey(String methodName, Class[] params)
        {
            /** 
             * Should never be initialized with nulls, but to be safe we refuse 
             * to accept them.
             */
            this.methodName = (methodName != null) ? methodName : StringUtils.EMPTY;
            this.params = (params != null) ? params : ArrayUtils.EMPTY_CLASS_ARRAY;
        }

        /**
         * @see java.lang.Object#equals(java.lang.Object)
         */
        public boolean equals(Object o)
        {
            /** 
             * note we skip the null test for methodName and params
             * due to the earlier test in the constructor
             */            
            if (o instanceof MethodCacheKey) 
            {
                final MethodCacheKey other = (MethodCacheKey) o;                
                if (params.length == other.params.length && 
                        methodName.equals(other.methodName)) 
                {              
                    for (int i = 0; i < params.length; ++i) 
                    {
                        if (params[i] == null)
                        {
                            if (params[i] != other.params[i])
                            {
                                return false;
                            }
                        }
                        else if (!params[i].equals(other.params[i]))
                        {
                            return false;
                        }
                    }
                    return true;
                }
            }
            return false;
        }
        

        /**
         * @see java.lang.Object#hashCode()
         */
        public int hashCode()
        {
            int result = 17;

            /** 
             * note we skip the null test for methodName and params
             * due to the earlier test in the constructor
             */            
            for (int i = 0; i < params.length; ++i)
            {
                final Class param = params[i];
                if (param != null)
                {
                    result = result * 37 + param.hashCode();
                }
            }
            
            result = result * 37 + methodName.hashCode();

            return result;
        } 
    }
    
}