org.apache.juneau.utils.PojoMerge Maven / Gradle / Ivy
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// * *
// * http://www.apache.org/licenses/LICENSE-2.0 *
// * *
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package org.apache.juneau.utils;
import java.lang.reflect.*;
/**
* Utility class for merging POJOs behind a single interface.
*
*
* Useful in cases where you want to define beans with 'default' values.
*
*
* For example, given the following bean classes...
*
*
* public interface IA {
* String getX();
* void setX(String x);
* }
*
* public class A implements IA {
* private String x ;
*
* public A(String x) {
* this .x = x;
* }
*
* public String getX() {
* return x ;
* }
*
* public void setX(String x) {
* this .x = x;
* }
* }
*
*
*
* The getters will be called in order until the first non-null value is returned...
*
*
* PojoMerge m;
*
* m = PojoMerge.merge (IA.class , new A("1" ), new A("2" ));
* assertEquals ("1" , m.getX());
*
* m = PojoMerge.merge (IA.class , new A(null ), new A("2" ));
* assertEquals ("2" , m.getX());
*
* m = PojoMerge.merge (IA.class , new A(null ), new A(null ));
* assertEquals (null , m.getX());
*
*
* Notes:
*
* - Null POJOs are ignored.
*
- Non-getter methods are either invoked on the first POJO or all POJOs depending on the
callAllNonGetters flag
* passed into the constructor.
* - For purposes of this interface, a getter is any method with zero arguments and a non-
void return type.
*
*/
public class PojoMerge {
/**
* Create a proxy interface on top of zero or more POJOs.
*
*
* This is a shortcut to calling merge(interfaceClass, false , pojos);
*
* @param interfaceClass The common interface class.
* @param pojos
* Zero or more POJOs to merge.
*
Can contain nulls.
* @return A proxy interface over the merged POJOs.
*/
@SuppressWarnings("unchecked")
public static T merge(Class interfaceClass, T...pojos) {
return merge(interfaceClass, false, pojos);
}
/**
* Create a proxy interface on top of zero or more POJOs.
*
* @param interfaceClass The common interface class.
* @param callAllNonGetters
* If true , when calling a method that's not a getter, the method will be invoked on all POJOs.
*
Otherwise, the method will only be called on the first POJO.
* @param pojos
* Zero or more POJOs to merge.
*
Can contain nulls.
* @return A proxy interface over the merged POJOs.
*/
@SuppressWarnings("unchecked")
public static T merge(Class interfaceClass, boolean callAllNonGetters, T...pojos) {
return (T)Proxy.newProxyInstance(interfaceClass.getClassLoader(), new Class[] { interfaceClass }, new PojoMergeInvocationHandler(callAllNonGetters, pojos));
}
private static class PojoMergeInvocationHandler implements InvocationHandler {
private final Object[] pojos;
private final boolean callAllNonGetters;
public PojoMergeInvocationHandler(boolean callAllNonGetters, Object...pojos) {
this.callAllNonGetters = callAllNonGetters;
this.pojos = pojos;
}
/**
* Implemented to handle the method called.
* @throws InvocationTargetException
* @throws IllegalAccessException
* @throws IllegalArgumentException
*/
@Override /* InvocationHandler */
public Object invoke(Object proxy, Method method, Object[] args) throws IllegalArgumentException, IllegalAccessException, InvocationTargetException {
Object r = null;
boolean isGetter = args == null && method.getReturnType() != Void.class;
for (Object pojo : pojos) {
if (pojo != null) {
r = method.invoke(pojo, args);
if (isGetter) {
if (r != null)
return r;
} else {
if (! callAllNonGetters)
return r;
}
}
}
return r;
}
}
}