querydsl/src/main/java/com/mysema/query/grammar/Visitor.java

/*
 * Copyright (c) 2008 Mysema Ltd.
 * All rights reserved.
 * 
 */
package com.mysema.query.grammar;

import java.lang.reflect.Method;

import com.mysema.core.collection.FactoryMap;
import com.mysema.query.grammar.Types.*;

/** 
 * Visitor provides a dispatching Visitor for Expr instances
 *
 * @author tiwe
 * @version $Id$
 */
public abstract class Visitor<T extends Visitor<T>> {
    
    private final FactoryMap<Class<?>,Method> methodMap = new FactoryMap<Class<?>,Method>(){

        @Override
        protected Method create(Class<?> cl) {
            try {
                if (PathEntity.class.isAssignableFrom(cl)){
                    cl = PathEntity.class;
                }
                Method method = null;
                Class<?> sigClass = Visitor.this.getClass();
                while (method == null && !sigClass.equals(Visitor.class)){
                    try{
                        method = sigClass.getDeclaredMethod("visit", cl);    
                    }catch(NoSuchMethodException nsme){
                        sigClass = sigClass.getSuperclass();
                    }                       
                }
                if (method != null){
                    method.setAccessible(true);    
                }else{
                    throw new IllegalArgumentException("No method found for " + cl.getSimpleName());
                }
                return method;
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
        
    };
    
    @SuppressWarnings("unchecked")
    public final T handle(Expr<?> expr){
        try {
            methodMap.get(expr.getClass()).invoke(this, expr);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return (T) this;
    }
    
    protected abstract void visit(Alias<?> expr);
    
    protected abstract void visit(AliasCollection<?> expr);
    
    protected abstract void visit(AliasEntity<?> expr);
    
    protected abstract void visit(AliasNoEntity<?> expr);
    
    protected abstract void visit(ConstantExpr<?> expr);
    
    protected abstract void visit(OperationBinary<?,?,?,?> expr);
    
    protected abstract void visit(OperationBinaryBoolean<?,?> expr);
    
    protected abstract void visit(OperationNoArg<?,?> expr);
    
    protected abstract void visit(OperationTertiary<?,?,?,?,?> expr);
    
    protected abstract void visit(OperationTertiaryBoolean<?,?,?> expr);
    
    protected abstract void visit(OperationUnary<?,?,?> expr);
    
    protected abstract void visit(OperationUnaryBoolean<?> expr);
    
    protected abstract void visit(Path<?> expr);
    
    protected abstract void visit(PathBoolean expr);
    
    protected abstract void visit(PathEntity<?> expr);
    
    protected abstract void visit(PathEntityCollection<?> expr);
    
    protected abstract void visit(PathNoEntity<?> expr);
    
}