MasterConverter.
+ * A MasterConverter is capable of converting between many different
+ * source and destination types. The MasterConverter
+ * delegates to other converters that do the actual work.
+ *
+ * To use this class you must subclass it, overide the + * (@link #createConverter(String)) method and register some + * converters using the (@link #registerConverter(String,String,String)) + * method.
+ * + *The reason this class deals with strings rather than Class objects + * is because dealing with strings allows us to implement alternative + * mechanisms for defining Converters in the future, only defining converter + * when it is first used.
+ * + * @author Peter Donald + * @version $Revision$ $Date$ + */ +public class AbstractMasterConverter + implements Converter +{ + private final static Resources REZ = + ResourceManager.getPackageResources( DefaultMasterConverter.class ); + + /** + * Map from converter classname to instance of converter. + */ + private final Map m_converters = new HashMap(); + + /** + * This holds the mapping between source/destination + * and converter name. + */ + private final HashMap m_mapping = new HashMap(); + + /** + * Convert object to destination type. + * + * @param destination the destination type + * @param original the original object + * @param context the context in which to convert + * @return the converted object + * @exception ConverterException if an error occurs + */ + public Object convert( final Class destination, + final Object original, + final Object context ) + throws ConverterException + { + final Class originalClass = original.getClass(); + + if( destination.isAssignableFrom( originalClass ) ) + { + return original; + } + + try + { + // Search inheritance hierarchy for converter + final String name = findConverter( originalClass, destination ); + + // Create the converter + Converter converter = (Converter)m_converters.get( name ); + if( converter == null ) + { + converter = createConverter( name ); + m_converters.put( name, converter ); + } + + // Convert + final Object object = converter.convert( destination, original, context ); + if( destination.isInstance( object ) ) + { + return object; + } + + final String message = + REZ.getString( "bad-return-type.error", + object.getClass().getName(), + destination.getName() ); + throw new ConverterException( message ); + } + catch( final Exception e ) + { + final String message = REZ.getString( "convert.error", + originalClass.getName(), + destination.getName() ); + throw new ConverterException( message, e ); + } + } + + /** + * Register a converter + * + * @param classname the className of converter + * @param source the source classname + * @param destination the destination classname + */ + protected void registerConverter( final String classname, + final String source, + final String destination ) + { + HashMap map = (HashMap)m_mapping.get( source ); + if( null == map ) + { + map = new HashMap(); + m_mapping.put( source, map ); + } + + map.put( destination, classname ); + + //Remove instance of converter if it has already been created + m_converters.remove( classname ); + } + + /** + * Create an instance of converter with specified name. + * + * @param name the name of converter + * @return the created converter instance + * @throws Exception if converter can not be created. + */ + protected abstract Converter createConverter( final String name ) + throws Exception; + + /** + * Determine the name of the converter to use to convert between + * original and destination classes. + */ + private String findConverter( final Class originalClass, + final Class destination ) + throws ConverterException + { + //TODO: Maybe we should search the destination classes hierarchy as well + + // Recursively iterate over the super-types of the original class, + // looking for a converter from source type -> destination type. + // If more than one is found, choose the most specialised. + + Class match = null; + String converterName = null; + ArrayList queue = new ArrayList(); + queue.add( originalClass ); + + while( !queue.isEmpty() ) + { + Class clazz = (Class)queue.remove( 0 ); + + // Add superclass and all interfaces + if( clazz.getSuperclass() != null ) + { + queue.add( clazz.getSuperclass() ); + } + final Class[] interfaces = clazz.getInterfaces(); + for( int i = 0; i < interfaces.length; i++ ) + { + queue.add( interfaces[ i ] ); + } + + // Check if we can convert from current class to destination + final String name = getConverterClassname( clazz.getName(), + destination.getName() ); + if( name == null ) + { + continue; + } + + // Choose the more specialised source class + if( match == null || match.isAssignableFrom( clazz ) ) + { + match = clazz; + converterName = name; + } + else if( clazz.isAssignableFrom( clazz ) ) + { + continue; + } + else + { + // Duplicate + final String message = REZ.getString( "ambiguous-converter.error" ); + throw new ConverterException( message ); + } + } + + // TODO - should cache the (src, dest) -> converter mapping + if( match != null ) + { + return converterName; + } + + // Could not find a converter + final String message = REZ.getString( "no-converter.error" ); + throw new ConverterException( message ); + } + + /** + * Retrieve name of ConverterInfo that describes converter that converts + * from source to destination. + * + * @param source the source classname + * @param destination the destination classname + * @return the className of converter or null if none available + */ + private String getConverterClassname( final String source, final String destination ) + { + final HashMap map = (HashMap)m_mapping.get( source ); + if( null == map ) + { + return null; + } + return (String)map.get( destination ); + } +} diff --git a/proposal/myrmidon/src/java/org/apache/myrmidon/components/converter/DefaultMasterConverter.java b/proposal/myrmidon/src/java/org/apache/myrmidon/components/converter/DefaultMasterConverter.java index 7499f3936..78ed0d69f 100644 --- a/proposal/myrmidon/src/java/org/apache/myrmidon/components/converter/DefaultMasterConverter.java +++ b/proposal/myrmidon/src/java/org/apache/myrmidon/components/converter/DefaultMasterConverter.java @@ -7,19 +7,13 @@ */ package org.apache.myrmidon.components.converter; -import java.util.ArrayList; -import java.util.HashMap; -import java.util.Map; import org.apache.aut.converter.Converter; -import org.apache.aut.converter.ConverterException; -import org.apache.avalon.excalibur.i18n.ResourceManager; -import org.apache.avalon.excalibur.i18n.Resources; import org.apache.avalon.framework.service.ServiceException; import org.apache.avalon.framework.service.ServiceManager; import org.apache.avalon.framework.service.Serviceable; +import org.apache.myrmidon.interfaces.converter.ConverterRegistry; import org.apache.myrmidon.interfaces.type.TypeFactory; import org.apache.myrmidon.interfaces.type.TypeManager; -import org.apache.myrmidon.interfaces.converter.ConverterRegistry; /** * Converter engine to handle converting between types. @@ -28,24 +22,11 @@ import org.apache.myrmidon.interfaces.converter.ConverterRegistry; * @version $Revision$ $Date$ */ public class DefaultMasterConverter - implements Converter, ConverterRegistry, Serviceable + extends AbstractMasterConverter + implements ConverterRegistry, Serviceable { - private final static Resources REZ = - ResourceManager.getPackageResources( DefaultMasterConverter.class ); - private TypeManager m_typeManager; - /** - * Map from converter classname to instance of converter. - */ - private final Map m_converters = new HashMap(); - - /** - * This holds the mapping between source/destination - * and converter name. - */ - private final HashMap m_mapping = new HashMap(); - /** * Retrieve relevent services needed to deploy. * @@ -69,70 +50,7 @@ public class DefaultMasterConverter final String source, final String destination ) { - HashMap map = (HashMap)m_mapping.get( source ); - if( null == map ) - { - map = new HashMap(); - m_mapping.put( source, map ); - } - - map.put( destination, className ); - } - - /** - * Convert object to destination type. - * - * @param destination the destination type - * @param original the original object - * @param context the context in which to convert - * @return the converted object - * @exception ConverterException if an error occurs - */ - public Object convert( final Class destination, - final Object original, - final Object context ) - throws ConverterException - { - final Class originalClass = original.getClass(); - - if( destination.isAssignableFrom( originalClass ) ) - { - return original; - } - - try - { - // Search inheritance hierarchy for converter - final String name = findConverter( originalClass, destination ); - - // Create the converter - Converter converter = (Converter)m_converters.get( name ); - if( converter == null ) - { - converter = createConverter( name ); - m_converters.put( name, converter ); - } - - // Convert - final Object object = converter.convert( destination, original, context ); - if( destination.isInstance( object ) ) - { - return object; - } - - final String message = - REZ.getString( "bad-return-type.error", - object.getClass().getName(), - destination.getName() ); - throw new ConverterException( message ); - } - catch( final Exception e ) - { - final String message = REZ.getString( "convert.error", - originalClass.getName(), - destination.getName() ); - throw new ConverterException( message, e ); - } + super.registerConverter( className, source, destination ); } /** @@ -142,99 +60,10 @@ public class DefaultMasterConverter * @return the created converter instance * @throws Exception if converter can not be created. */ - private Converter createConverter( final String name ) + protected Converter createConverter( final String name ) throws Exception { final TypeFactory factory = m_typeManager.getFactory( Converter.ROLE ); return (Converter)factory.create( name ); } - - /** - * Determine the name of the converter to use to convert between - * original and destination classes. - */ - private String findConverter( final Class originalClass, - final Class destination ) - throws ConverterException - { - //TODO: Maybe we should search the destination classes hierarchy as well - - // Recursively iterate over the super-types of the original class, - // looking for a converter from source type -> destination type. - // If more than one is found, choose the most specialised. - - Class match = null; - String converterName = null; - ArrayList queue = new ArrayList(); - queue.add( originalClass ); - - while( !queue.isEmpty() ) - { - Class clazz = (Class)queue.remove( 0 ); - - // Add superclass and all interfaces - if( clazz.getSuperclass() != null ) - { - queue.add( clazz.getSuperclass() ); - } - final Class[] interfaces = clazz.getInterfaces(); - for( int i = 0; i < interfaces.length; i++ ) - { - queue.add( interfaces[ i ] ); - } - - // Check if we can convert from current class to destination - final String name = getConverterClassname( clazz.getName(), - destination.getName() ); - if( name == null ) - { - continue; - } - - // Choose the more specialised source class - if( match == null || match.isAssignableFrom( clazz ) ) - { - match = clazz; - converterName = name; - } - else if( clazz.isAssignableFrom( clazz ) ) - { - continue; - } - else - { - // Duplicate - final String message = REZ.getString( "ambiguous-converter.error" ); - throw new ConverterException( message ); - } - } - - // TODO - should cache the (src, dest) -> converter mapping - if( match != null ) - { - return converterName; - } - - // Could not find a converter - final String message = REZ.getString( "no-converter.error" ); - throw new ConverterException( message ); - } - - /** - * Retrieve name of ConverterInfo that describes converter that converts - * from source to destination. - * - * @param source the source classname - * @param destination the destination classname - * @return the className of converter or null if none available - */ - private String getConverterClassname( final String source, final String destination ) - { - final HashMap map = (HashMap)m_mapping.get( source ); - if( null == map ) - { - return null; - } - return (String)map.get( destination ); - } }