java反射(Field的应用)

//$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 {

public static final class DirectGetter implements Getter {
private final transient Field field;
private final Class clazz;
private final 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) {
throw new 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() {
return null;
}
public String getMethodName() {
return null;
}
public Class getReturnType() {
return field.getType();
}

Object readResolve() {
return new DirectGetter( getField(clazz, name), clazz, name );
}

public String toString() {
return "DirectGetter(" + clazz.getName() + '.' + name + ')';
}
}

public static final class DirectSetter implements Setter {
private final transient Field field;
private final Class clazz;
private final String name;
DirectSetter(Field field, Class clazz, String name) {
this.field = field;
this.clazz = clazz;
this.name = name;
}
public Method getMethod() {
return null;
}
public String getMethodName() {
return null;
}
public void 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()) {
throw new PropertyAccessException(
e,
"Null value was assigned to a property of primitive type",
true,
clazz,
name
);
} else {
throw new PropertyAccessException(e, "could not set a field value by reflection", true, clazz, name);
}
}
}

public String toString() {
return "DirectSetter(" + clazz.getName() + '.' + name + ')';
}

Object readResolve() {
return new DirectSetter( getField(clazz, name), clazz, name );
}
}

private static Field getField(Class clazz, String name) throws PropertyNotFoundException {
if ( clazz==null || clazz==Object.class ) {
throw new 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;
}

private static Field getField(Class root, Class clazz, String name) throws PropertyNotFoundException {
if ( clazz==null || clazz==Object.class ) {
throw new 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 {
return new DirectGetter( getField(theClass, propertyName), theClass, propertyName );
}

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

}