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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript.
It gets rid of almost all the boiler plate code between the web browser and your Java code.
/*
* Copyright 2005 Joe Walker
*
* 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.
*/
package org.directwebremoting.impl;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Map;
import java.util.TreeMap;
import javax.servlet.Servlet;
import org.directwebremoting.Container;
import org.directwebremoting.util.LocalUtil;
import org.directwebremoting.util.Logger;
/**
* DefaultContainer is like a mini-IoC container for DWR.
* At least it is an IoC container by interface (check: no params that have
* anything to do with DWR), but it is hard coded specifically for DWR. If we
* want to make more of it we can later, but this is certainly not going to
* become a full blown IoC container.
* @author Joe Walker [joe at getahead dot ltd dot uk]
*/
public class DefaultContainer extends AbstractContainer implements Container
{
/**
* Set the class that should be used to implement the given interface
* @param askFor The interface to implement
* @param valueParam The new implementation
* @throws IllegalAccessException If the specified beans could not be accessed
* @throws InstantiationException If the specified beans could not be created
*/
public void addParameter(Object askFor, Object valueParam) throws InstantiationException, IllegalAccessException
{
Object value = valueParam;
// Maybe the value is a classname that needs instansiating
if (value instanceof String)
{
try
{
Class impl = LocalUtil.classForName((String) value);
value = impl.newInstance();
}
catch (ClassNotFoundException ex)
{
// it's not a classname, leave it
}
}
// If we have an instansiated value object and askFor is an interface
// then we can check that one implements the other
if (!(value instanceof String) && askFor instanceof String)
{
try
{
Class iface = LocalUtil.classForName((String) askFor);
if (!iface.isAssignableFrom(value.getClass()))
{
log.error("Can't cast: " + value + " to " + askFor);
}
}
catch (ClassNotFoundException ex)
{
// it's not a classname, leave it
}
}
if (log.isDebugEnabled())
{
if (value instanceof String)
{
log.debug("Adding IoC setting: " + askFor + "=" + value);
}
else
{
log.debug("Adding IoC implementation: " + askFor + "=" + value.getClass().getName());
}
}
beans.put(askFor, value);
}
/**
* Called to indicate that we finished adding parameters.
* The thread safety of a large part of DWR depends on this function only
* being called from {@link Servlet#init(javax.servlet.ServletConfig)},
* where all the setup is done, and where we depend on the undocumented
* feature of all servlet containers that they complete the init process
* of a Servlet before they begin servicing requests.
* @see DefaultContainer#addParameter(Object, Object)
* @noinspection UnnecessaryLabelOnContinueStatement
*/
public void setupFinished()
{
// We try to autowire each bean in turn
for (Iterator it = beans.entrySet().iterator(); it.hasNext();)
{
Map.Entry entry = (Map.Entry) it.next();
// Class type = (Class) entry.getKey();
Object ovalue = entry.getValue();
if (!(ovalue instanceof String))
{
log.debug("Trying to autowire: " + ovalue.getClass().getName());
Method[] methods = ovalue.getClass().getMethods();
methods:
for (int i = 0; i < methods.length; i++)
{
Method setter = methods[i];
if (setter.getName().startsWith("set") &&
setter.getName().length() > 3 &&
setter.getParameterTypes().length == 1)
{
String name = Character.toLowerCase(setter.getName().charAt(3)) + setter.getName().substring(4);
Class propertyType = setter.getParameterTypes()[0];
// First we try auto-wire by name
Object setting = beans.get(name);
if (setting != null)
{
if (propertyType.isAssignableFrom(setting.getClass()))
{
log.debug("- autowire-by-name: " + name + "=" + setting);
invoke(setter, ovalue, setting);
continue methods;
}
else if (setting.getClass() == String.class)
{
try
{
Object value = LocalUtil.simpleConvert((String) setting, propertyType);
log.debug("- autowire-by-name: " + name + "=" + value);
invoke(setter, ovalue, value);
}
catch (IllegalArgumentException ex)
{
// Ignore - this was a specuative convert anyway
}
continue methods;
}
}
// Next we try autowire-by-type
Object value = beans.get(propertyType.getName());
if (value != null)
{
log.debug("- autowire-by-type: " + name + "=" + value.getClass().getName());
invoke(setter, ovalue, value);
continue methods;
}
log.debug("- skipped autowire: " + name);
}
}
}
}
callInitializingBeans();
}
/**
* A helper to do the reflection.
* This helper throws away all exceptions, prefering to log.
* @param setter The method to invoke
* @param bean The object to invoke the method on
* @param value The value to assign to the property using the setter method
*/
private static void invoke(Method setter, Object bean, Object value)
{
try
{
setter.invoke(bean, new Object[] { value });
}
catch (IllegalArgumentException ex)
{
log.error("- Internal error: " + ex.getMessage());
}
catch (IllegalAccessException ex)
{
log.error("- Permission error: " + ex.getMessage());
}
catch (InvocationTargetException ex)
{
log.error("- Exception during auto-wire: ", ex.getTargetException());
}
}
/* (non-Javadoc)
* @see org.directwebremoting.Container#getBean(java.lang.String)
*/
public Object getBean(String id)
{
Object reply = beans.get(id);
if (reply == null)
{
log.debug("DefaultContainer: No bean with id=" + id);
}
return reply;
}
/* (non-Javadoc)
* @see org.directwebremoting.Container#getBeanNames()
*/
public Collection getBeanNames()
{
return Collections.unmodifiableCollection(beans.keySet());
}
/**
* The beans that we know of indexed by type
*/
protected Map beans = new TreeMap();
/**
* The log stream
*/
private static final Logger log = Logger.getLogger(DefaultContainer.class);
}
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