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java反射(Field的应用)

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            //
            $Id: DirectPropertyAccessor.java 11405 2007-04-15 12:50:34Z max.andersen@jboss.com $
            package
             org.hibernate.property;


            import
             java.lang.reflect.Field;

            import
             java.lang.reflect.Method;

            import
             java.util.Map;


            import
             org.hibernate.HibernateException;

            import
             org.hibernate.PropertyAccessException;

            import
             org.hibernate.PropertyNotFoundException;

            import
             org.hibernate.engine.SessionFactoryImplementor;

            import
             org.hibernate.engine.SessionImplementor;

            import
             org.hibernate.util.ReflectHelper;


            /**
            
 * Accesses fields directly.
 * 
            @author
             Gavin King
 
            */
            public
            class DirectPropertyAccessor implements PropertyAccessor {

    publicstaticfinalclass DirectGetter implements Getter {
        privatefinaltransient Field field;
        privatefinal Class clazz;
        privatefinal String name;
        DirectGetter(Field field, Class clazz, String name) {
            this.field = field;
            this.clazz = clazz;
            this.name = name;
        }
        public Object get(Object target) throws HibernateException {
            try {
                return field.get(target);//返回指定对象上此 Field 表示的字段的值。            }
            catch (Exception e) {
                thrownew PropertyAccessException(e, "could not get a field value by reflection", false, clazz, name);
            }
        }

        public Object getForInsert(Object target, Map mergeMap, SessionImplementor session) {
            return get( target );
        }

        public Method getMethod() {
            returnnull;
        }
        public String getMethodName() {
            returnnull;
        }
        public Class getReturnType() {
            return field.getType();
        }

        Object readResolve() {
            returnnew DirectGetter( getField(clazz, name), clazz, name );
        }
        
        public String toString() {
            return "DirectGetter(" + clazz.getName() + ‘.‘ + name + ‘)‘;
        }
    }

    publicstaticfinalclass DirectSetter implements Setter {
        privatefinaltransient Field field;
        privatefinal Class clazz;
        privatefinal String name;
        DirectSetter(Field field, Class clazz, String name) {
            this.field = field;
            this.clazz = clazz;
            this.name = name;
        }
        public Method getMethod() {
            returnnull;
        }
        public String getMethodName() {
            returnnull;
        }
        publicvoid set(Object target, Object value, SessionFactoryImplementor factory) throws HibernateException {
            try {
                field.set(target, value);//将指定对象变量上此 Field 对象表示的字段设置为指定的新值。            }
            catch (Exception e) {
                if(value == null && field.getType().isPrimitive()) {
                    thrownew PropertyAccessException(
                            e, 
                            "Null value was assigned to a property of primitive type", 
                            true, 
                            clazz, 
                            name
                        );                    
                } else {
                    thrownew PropertyAccessException(e, "could not set a field value by reflection", true, clazz, name);
                }
            }
        }

        public String toString() {
            return "DirectSetter(" + clazz.getName() + ‘.‘ + name + ‘)‘;
        }
        
        Object readResolve() {
            returnnew DirectSetter( getField(clazz, name), clazz, name );
        }
    }

    privatestatic Field getField(Class clazz, String name) throws PropertyNotFoundException {
        if ( clazz==null || clazz==Object.class ) {
            thrownew PropertyNotFoundException("field not found: " + name); 
        }
        Field field;
        try {
            field = clazz.getDeclaredField(name);//返回一个 Field 对象，该对象反映此 Class 对象所表示的类或接口的指定已声明字段。        }
        catch (NoSuchFieldException nsfe) {
            field = getField( clazz, clazz.getSuperclass(), name );
        }
        if ( !ReflectHelper.isPublic(clazz, field) ) field.setAccessible(true);
        return field;
    }

    privatestatic Field getField(Class root, Class clazz, String name) throws PropertyNotFoundException {
        if ( clazz==null || clazz==Object.class ) {
            thrownew PropertyNotFoundException("field [" + name + "] not found on " + root.getName()); 
        }
        Field field;
        try {
            field = clazz.getDeclaredField(name);
        }
        catch (NoSuchFieldException nsfe) {
            field = getField( root, clazz.getSuperclass(), name );
        }
        if ( !ReflectHelper.isPublic(clazz, field) ) field.setAccessible(true);
        return field;
    }
    
    public Getter getGetter(Class theClass, String propertyName)
        throws PropertyNotFoundException {
        returnnew DirectGetter( getField(theClass, propertyName), theClass, propertyName );
    }

    public Setter getSetter(Class theClass, String propertyName)
        throws PropertyNotFoundException {
        returnnew DirectSetter( getField(theClass, propertyName), theClass, propertyName );
    }

}

 

原文：http://www.cnblogs.com/toSeeMyDream/p/4378966.html

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