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package org.apache.velocity.app;
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.velocity.util.ClassUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.HashMap;
import java.util.Map;
/**
* <p>
* This is a small utility class allow easy access to static fields in a class,
* such as string constants. Velocity will not introspect for class
* fields (and won't in the future :), but writing setter/getter methods to do
* this really is a pain, so use this if you really have
* to access fields.
*
* <p>
* The idea it so enable access to the fields just like you would in Java.
* For example, in Java, you would access a static field like
* <blockquote><pre>
* MyClass.STRING_CONSTANT
* </pre></blockquote>
* and that is the same thing we are trying to allow here.
*
* <p>
* So to use in your Java code, do something like this :
* <blockquote><pre>
* context.put("runtime", new FieldMethodizer( "org.apache.velocity.runtime.Runtime" ));
* </pre></blockquote>
* and then in your template, you can access any of your static fields in this way :
* <blockquote><pre>
* $runtime.COUNTER_NAME
* </pre></blockquote>
*
* <p>
* Right now, this class only methodizes <code>public static</code> fields. It seems
* that anything else is too dangerous. This class is for convenience accessing
* 'constants'. If you have fields that aren't <code>static</code> it may be better
* to handle them by explicitly placing them into the context.
*
* @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
* @version $Id$
*/
public class FieldMethodizer
{
/** Hold the field objects by field name */
private Map<String, Field> fieldHash = new HashMap<>();
private Logger logger = LoggerFactory.getLogger(FieldMethodizer.class);
/**
* Allow object to be initialized without any data. You would use
* addObject() to add data later.
*/
public FieldMethodizer()
{
}
/**
* Constructor that takes as it's arg the name of the class
* to methodize.
*
* @param s Name of class to methodize.
*/
public FieldMethodizer( String s )
{
try
{
addObject(s);
}
catch( Exception e )
{
logger.error("[FieldMethodizer] Could not add {} for field methodizing", s, e);
}
}
/**
* Constructor that takes as it's arg a living
* object to methodize. Note that it will still
* only methodized the public static fields of
* the class.
*
* @param o Name of class to methodize.
*/
public FieldMethodizer( Object o )
{
try
{
addObject(o);
}
catch( Exception e )
{
logger.error("[FieldMethodizer] Could not add {} for field methodizing", o, e);
}
}
/**
* Add the Name of the class to methodize
* @param s
* @throws Exception
*/
public void addObject ( String s )
throws Exception
{
inspect(ClassUtils.getClass(s));
}
/**
* Add an Object to methodize
* @param o
* @throws Exception
*/
public void addObject ( Object o )
throws Exception
{
inspect(o.getClass());
}
/**
* Accessor method to get the fields by name.
*
* @param fieldName Name of static field to retrieve
*
* @return The value of the given field.
*/
public Object get( String fieldName )
{
Object value = null;
try
{
Field f = fieldHash.get( fieldName );
if (f != null)
{
value = f.get(null);
}
}
catch( IllegalAccessException e )
{
System.err.println("IllegalAccessException while trying to access " + fieldName
+ ": " + e.getMessage());
}
return value;
}
/**
* Method that retrieves all public static fields
* in the class we are methodizing.
*/
private void inspect(Class<?> clas)
{
Field[] fields = clas.getFields();
for (Field field : fields)
{
/*
* only if public and static
*/
int mod = field.getModifiers();
if (Modifier.isStatic(mod) && Modifier.isPublic(mod))
{
fieldHash.put(field.getName(), field);
}
}
}
}
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