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BeanUtils provides an easy-to-use but flexible wrapper around reflection and introspection.

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package org.apache.commons.beanutils;

/**
 * 

DynaClass which implements the MutableDynaClass interface.

* *

A MutableDynaClass is a specialized extension to DynaClass * that allows properties to be added or removed dynamically.

* *

This implementation has one slightly unusual default behaviour - calling * the getDynaProperty(name) method for a property which doesn't * exist returns a DynaProperty rather than null. The * reason for this is that BeanUtils calls this method to check if * a property exists before trying to set the value. This would defeat the object * of the LazyDynaBean which automatically adds missing properties * when any of its set() methods are called. For this reason the * isDynaProperty(name) method has been added to this implementation * in order to determine if a property actually exists. If the more normal * behaviour of returning null is required, then this can be achieved * by calling the setReturnNull(true).

* *

The add(name, type, readable, writable) method is not implemented * and always throws an UnsupportedOperationException. I believe * this attributes need to be added to the DynaProperty class * in order to control read/write facilities.

* * @see LazyDynaBean * @author Niall Pemberton */ public class LazyDynaClass extends BasicDynaClass implements MutableDynaClass { /** * Controls whether changes to this DynaClass's properties are allowed. */ protected boolean restricted; /** *

Controls whether the getDynaProperty() method returns * null if a property doesn't exist - or creates a new one.

* *

Default is false. */ protected boolean returnNull = false; /** * Construct a new LazyDynaClass with default parameters. */ public LazyDynaClass() { this(null, (DynaProperty[])null); } /** * Construct a new LazyDynaClass with the specified name. * * @param name Name of this DynaBean class */ public LazyDynaClass(String name) { this(name, (DynaProperty[])null); } /** * Construct a new LazyDynaClass with the specified name and DynaBean class. * * @param name Name of this DynaBean class * @param dynaBeanClass The implementation class for new instances */ public LazyDynaClass(String name, Class dynaBeanClass) { this(name, dynaBeanClass, null); } /** * Construct a new LazyDynaClass with the specified name and properties. * * @param name Name of this DynaBean class * @param properties Property descriptors for the supported properties */ public LazyDynaClass(String name, DynaProperty[] properties) { this(name, LazyDynaBean.class, properties); } /** * Construct a new LazyDynaClass with the specified name, DynaBean class and properties. * * @param name Name of this DynaBean class * @param dynaBeanClass The implementation class for new intances * @param properties Property descriptors for the supported properties */ public LazyDynaClass(String name, Class dynaBeanClass, DynaProperty properties[]) { super(name, dynaBeanClass, properties); } /** *

Is this DynaClass currently restricted.

*

If restricted, no changes to the existing registration of * property names, data types, readability, or writeability are allowed.

* @return true if this {@link MutableDynaClass} cannot be changed * otherwise false */ public boolean isRestricted() { return restricted; } /** *

Set whether this DynaClass is currently restricted.

*

If restricted, no changes to the existing registration of * property names, data types, readability, or writeability are allowed.

* @param restricted true if this {@link MutableDynaClass} cannot * be changed otherwise false */ public void setRestricted(boolean restricted) { this.restricted = restricted; } /** * Should this DynaClass return a null from * the getDynaProperty(name) method if the property * doesn't exist. * * @return true if a null {@link DynaProperty} * should be returned if the property doesn't exist, otherwise * false if a new {@link DynaProperty} should be created. */ public boolean isReturnNull() { return returnNull; } /** * Set whether this DynaClass should return a null from * the getDynaProperty(name) method if the property * doesn't exist. * @param returnNull true if a null {@link DynaProperty} * should be returned if the property doesn't exist, otherwise * false if a new {@link DynaProperty} should be created. */ public void setReturnNull(boolean returnNull) { this.returnNull = returnNull; } /** * Add a new dynamic property with no restrictions on data type, * readability, or writeability. * * @param name Name of the new dynamic property * * @exception IllegalArgumentException if name is null * @exception IllegalStateException if this DynaClass is currently * restricted, so no new properties can be added */ public void add(String name) { add(new DynaProperty(name)); } /** * Add a new dynamic property with the specified data type, but with * no restrictions on readability or writeability. * * @param name Name of the new dynamic property * @param type Data type of the new dynamic property (null for no * restrictions) * * @exception IllegalArgumentException if name is null * @exception IllegalStateException if this DynaClass is currently * restricted, so no new properties can be added */ public void add(String name, Class type) { if (type == null) { add(name); } else { add(new DynaProperty(name, type)); } } /** *

Add a new dynamic property with the specified data type, readability, * and writeability.

* *

N.B.Support for readable/writeable properties has not been implemented * and this method always throws a UnsupportedOperationException.

* *

I'm not sure the intention of the original authors for this method, but it seems to * me that readable/writable should be attributes of the DynaProperty class * (which they are not) and is the reason this method has not been implemented.

* * @param name Name of the new dynamic property * @param type Data type of the new dynamic property (null for no * restrictions) * @param readable Set to true if this property value * should be readable * @param writeable Set to true if this property value * should be writeable * * @exception UnsupportedOperationException anytime this method is called */ public void add(String name, Class type, boolean readable, boolean writeable) { throw new java.lang.UnsupportedOperationException("readable/writable properties not supported"); } /** * Add a new dynamic property. * * @param property Property the new dynamic property to add. * * @exception IllegalArgumentException if name is null * @exception IllegalStateException if this DynaClass is currently * restricted, so no new properties can be added */ protected void add(DynaProperty property) { if (property.getName() == null) { throw new IllegalArgumentException("Property name is missing."); } if (isRestricted()) { throw new IllegalStateException("DynaClass is currently restricted. No new properties can be added."); } // Check if property already exists if (propertiesMap.get(property.getName()) != null) { return; } // Create a new property array with the specified property DynaProperty[] oldProperties = getDynaProperties(); DynaProperty[] newProperties = new DynaProperty[oldProperties.length+1]; System.arraycopy(oldProperties, 0, newProperties, 0, oldProperties.length); newProperties[oldProperties.length] = property; // Update the properties setProperties(newProperties); } /** * Remove the specified dynamic property, and any associated data type, * readability, and writeability, from this dynamic class. * NOTE - This does NOT cause any * corresponding property values to be removed from DynaBean instances * associated with this DynaClass. * * @param name Name of the dynamic property to remove * * @exception IllegalArgumentException if name is null * @exception IllegalStateException if this DynaClass is currently * restricted, so no properties can be removed */ public void remove(String name) { if (name == null) { throw new IllegalArgumentException("Property name is missing."); } if (isRestricted()) { throw new IllegalStateException("DynaClass is currently restricted. No properties can be removed."); } // Ignore if property doesn't exist if (propertiesMap.get(name) == null) { return; } // Create a new property array of without the specified property DynaProperty[] oldProperties = getDynaProperties(); DynaProperty[] newProperties = new DynaProperty[oldProperties.length-1]; int j = 0; for (int i = 0; i < oldProperties.length; i++) { if (!(name.equals(oldProperties[i].getName()))) { newProperties[j] = oldProperties[i]; j++; } } // Update the properties setProperties(newProperties); } /** *

Return a property descriptor for the specified property.

* *

If the property is not found and the returnNull indicator is * true, this method always returns null.

* *

If the property is not found and the returnNull indicator is * false a new property descriptor is created and returned (although * its not actually added to the DynaClass's properties). This is the default * beahviour.

* *

The reason for not returning a null property descriptor is that * BeanUtils uses this method to check if a property exists * before trying to set it - since these Lazy implementations automatically * add any new properties when they are set, returning null from * this method would defeat their purpose.

* * @param name Name of the dynamic property for which a descriptor * is requested * @return The dyna property for the specified name * * @exception IllegalArgumentException if no property name is specified */ public DynaProperty getDynaProperty(String name) { if (name == null) { throw new IllegalArgumentException("Property name is missing."); } DynaProperty dynaProperty = (DynaProperty)propertiesMap.get(name); // If it doesn't exist and returnNull is false // create a new DynaProperty if (dynaProperty == null && !isReturnNull() && !isRestricted()) { dynaProperty = new DynaProperty(name); } return dynaProperty; } /** *

Indicate whether a property actually exists.

* *

N.B. Using getDynaProperty(name) == null * doesn't work in this implementation because that method might * return a DynaProperty if it doesn't exist (depending on the * returnNull indicator).

* * @param name The name of the property to check * @return true if there is a property of the * specified name, otherwise false * @exception IllegalArgumentException if no property name is specified */ public boolean isDynaProperty(String name) { if (name == null) { throw new IllegalArgumentException("Property name is missing."); } return propertiesMap.get(name) == null ? false : true; } }