JavaBean 备忘录

 

1. public class Introspector extends Object

The Introspector class provides a standard way for tools to learn about the properties, events, and methods supported by a target Java Bean.

For each of those three kinds of information, the Introspector will separately analyze the bean's class and superclasses looking for either explicit or implicit information and use that information to build a BeanInfo object that comprehensively describes the target bean.

For each class "Foo", explicit information may be available if there exists a corresponding "FooBeanInfo" class that provides a non-null value when queried for the information. We first look for the BeanInfo class by taking the full package-qualified name of the target bean class and appending "BeanInfo" to form a new class name. If this fails, then we take the final classname component of this name, and look for that class in each of the packages specified in the BeanInfo package search path.

Thus for a class such as "sun.xyz.OurButton" we would first look for a BeanInfo class called "sun.xyz.OurButtonBeanInfo" and if that failed we'd look in each package in the BeanInfo search path for an OurButtonBeanInfo class. With the default search path, this would mean looking for "sun.beans.infos.OurButtonBeanInfo".

If a class provides explicit BeanInfo about itself then we add that to the BeanInfo information we obtained from analyzing any derived classes, but we regard the explicit information as being definitive for the current class and its base classes, and do not proceed any further up the superclass chain.

If we don't find explicit BeanInfo on a class, we use low-level reflection to study the methods of the class and apply standard design patterns to identify property accessors, event sources, or public methods. We then proceed to analyze the class's superclass and add in the information from it (and possibly on up the superclass chain).

Because the Introspector caches BeanInfo classes for better performance, take care if you use it in an application that uses multiple class loaders. In general, when you destroy a ClassLoader that has been used to introspect classes, you should use the Introspector.flushCaches or Introspector.flushFromCaches method to flush all of the introspected classes out of the cache.

For more information about introspection and design patterns, please consult the JavaBeans specification.

 

2. public class PropertyEditorManager extends Object

The PropertyEditorManager can be used to locate a property editor for any given type name. This property editor must support the java.beans.PropertyEditor interface for editing a given object.

The PropertyEditorManager uses three techniques for locating an editor for a given type. First, it provides a registerEditor method to allow an editor to be specifically registered for a given type. Second it tries to locate a suitable class by adding "Editor" to the full qualified classname of the given type (e.g. "foo.bah.FozEditor"). Finally it takes the simple classname (without the package name) adds "Editor" to it and looks in a search-path of packages for a matching class.

So for an input class foo.bah.Fred, the PropertyEditorManager would first look in its tables to see if an editor had been registered for foo.bah.Fred and if so use that. Then it will look for a foo.bah.FredEditor class. Then it will look for (say) standardEditorsPackage.FredEditor class.

Default PropertyEditors will be provided for the Java primitive types "boolean", "byte", "short", "int", "long", "float", and "double"; and for the classes java.lang.String. java.awt.Color, and java.awt.Font.

 

3. Supply your own PropertyEditor

1. BeanInfo.getPropertyDescriptors()
2. PropertyDescriptor.setPropertyEditor() --> override PropertyEditorManager.registerEditor()

 

4. Serialization

Note, for JavaBean serialization, implementing the java.io.Serializable interface is not necessary. The XML long-term persistence mechanism introduced in J2SE 1.4 can save the state of a JavaBean in an XML format that is resilient to version changes in the implementation of that JavaBean. classes java.beans.XMLEncoder, java.beans.XMLDecoder, and java.beans.PersistenceDelegate.