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[DRAFT] Add support for factory methods in BeanMapper initialization #214

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[DRAFT] Add support for factory methods in BeanMapper initialization #214

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43 changes: 43 additions & 0 deletions src/main/java/io/beanmapper/annotations/BeanFactoryMethod.java
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Original file line number Diff line number Diff line change
@@ -0,0 +1,43 @@
package io.beanmapper.annotations;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
* Annotation to mark static factory methods for bean instantiation.
*
* <p>This annotation allows specifying static factory methods that can be used
* to instantiate objects during the bean mapping process. The factory method
* must be static since it will be called before any instance of the target
* type is available.</p>
*
* <p>The value array specifies the names of the fields that should be provided
* to the factory method as arguments, in the correct order.</p>
*
* <p>Example usage:</p>
* <pre>
* public class Person {
* private String name;
* private int age;
*
* &#64;BeanFactoryMethod({"name", "age"})
* public static Person create(String name, int age) {
* return new Person(name, age);
* }
* }
* </pre>
*/
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface BeanFactoryMethod {

/**
* The names of the fields that should be provided to the factory method
* as arguments, in the correct order.
*
* @return array of field names
*/
String[] value();
}
14 changes: 14 additions & 0 deletions src/main/java/io/beanmapper/config/BeanMapperBuilder.java
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Expand Up @@ -13,6 +13,7 @@
import io.beanmapper.core.collections.QueueCollectionHandler;
import io.beanmapper.core.collections.SetCollectionHandler;
import io.beanmapper.core.constructor.BeanInitializer;
import io.beanmapper.core.constructor.FactoryMethodAwareBeanInitializer;
import io.beanmapper.core.converter.BeanConverter;
import io.beanmapper.core.converter.collections.CollectionConverter;
import io.beanmapper.core.converter.impl.AnyToEnumConverter;
Expand Down Expand Up @@ -134,6 +135,19 @@ public BeanMapperBuilder setBeanInitializer(BeanInitializer beanInitializer) {
return this;
}

/**
* Enables factory method support by setting a FactoryMethodAwareBeanInitializer that will
* look for static methods annotated with @BeanFactoryMethod and use them for object
* instantiation when available. Falls back to the default bean initializer when no
* factory method is found.
*
* @return the builder for fluent configuration
*/
public BeanMapperBuilder withFactoryMethodSupport() {
this.configuration.setBeanInitializer(new FactoryMethodAwareBeanInitializer());
return this;
}

public BeanMapperBuilder setBeanUnproxy(BeanUnproxy beanUnproxy) {
this.configuration.setBeanUnproxy(beanUnproxy);
return this;
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70 changes: 70 additions & 0 deletions src/main/java/io/beanmapper/core/constructor/FactoryMethodAwareBeanInitializer.java
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/*
* (C) 2014 42 bv (www.42.nl). All rights reserved.
*/
package io.beanmapper.core.constructor;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import io.beanmapper.annotations.BeanFactoryMethod;
import io.beanmapper.strategy.ConstructorArguments;
import io.beanmapper.utils.BeanMapperTraceLogger;

/**
* A BeanInitializer that is aware of factory methods but integrates with the existing
* strategy framework. This initializer extends DefaultBeanInitializer but first checks
* for factory methods when no ConstructorArguments are provided.
*/
public class FactoryMethodAwareBeanInitializer extends DefaultBeanInitializer {

private final FactoryMethodBeanInitializer factoryMethodInitializer;

public FactoryMethodAwareBeanInitializer() {
this.factoryMethodInitializer = new FactoryMethodBeanInitializer(this);
}

/**
* {@inheritDoc}
*/
@Override
public <T> T instantiate(Class<T> beanClass, ConstructorArguments arguments) {
// If we have constructor arguments, use the factory method initializer
// which can handle both factory methods and fallback to default behavior
if (arguments != null) {
return factoryMethodInitializer.instantiate(beanClass, arguments);
}

// If no constructor arguments, check if there's a factory method that requires no arguments
Method factoryMethod = findNoArgFactoryMethod(beanClass);
if (factoryMethod != null) {
return factoryMethodInitializer.instantiate(beanClass, null);
}

// Fall back to default behavior (no-arg constructor)
return super.instantiate(beanClass, null);
}

/**
* Finds a factory method that requires no arguments.
*
* @param beanClass the target class
* @return a no-arg factory method, or null if none found
*/
private Method findNoArgFactoryMethod(Class<?> beanClass) {
for (Method method : beanClass.getDeclaredMethods()) {
if (method.isAnnotationPresent(BeanFactoryMethod.class) &&
Modifier.isStatic(method.getModifiers()) &&
beanClass.isAssignableFrom(method.getReturnType()) &&
method.getParameterCount() == 0) {

BeanFactoryMethod annotation = method.getAnnotation(BeanFactoryMethod.class);
if (annotation.value().length == 0) {
BeanMapperTraceLogger.log("Found no-arg factory method {} for class {}",
method.getName(), beanClass.getName());
return method;
}
}
}
return null;
}
}
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