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6. JSF: Weld CDI and Reflection. Using reflection on injected objects.

0. Introduction


Weld and Reflection are not good friends. When you inject a bean into another, Weld CDI makes a proxy of the injected object. So when you want to obtain information using Reflection, you cannot see the original injected object.

BalusC gives us the clue to introspect a Weld proxy bean. He uses BeanInfo Interface from the Java Beans API.

By means of this Bean API, we can retrieve the original object from the proxy object. It is stored in the attribute  targetInstance. Once we have this original object, we can use reflection. 
Note: To use Weld with Tomcat, we must include this dependency in the pom.xml file

 
<!-- https://mvnrepository.com/artifact/org.jboss.weld.servlet/weld-servlet-shaded -->
<dependency>
    <groupId>org.jboss.weld.servlet</groupId>
    <artifactId>weld-servlet-shaded</artifactId>
    <version>3.0.5.Final</version>
</dependency>




1. A simple example

Let's consider 2 simple beans, Bean1 and Bean2, and Bean1 is injected into Bean2.

Bean1.java

 
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package org.ximodante.jsf.provesalfred;

import java.io.Serializable;

import javax.enterprise.context.SessionScoped;
import javax.inject.Named;

import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import lombok.ToString;

@Named @ToString @SessionScoped @NoArgsConstructor
public class Bean1 implements Serializable{
 private static final long serialVersionUID = 1L;
    
 @Getter @Setter private String field1="a";
 
}


Bean2.java

 
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import java.io.Serializable;
import javax.faces.view.ViewScoped;
import javax.inject.Inject;
import javax.inject.Named;


import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Named @ToString @ViewScoped
public class Bean2 implements Serializable{
 private static final long serialVersionUID = 1L;
    
 @Inject @Getter @Setter private Bean1 b1;
    
 @Getter @Setter private String field2="33";
 
 public String go() {
  System.out.println("HELLO!");
  
  System.out.println("1. Displaying fields from beans");
  System.out.println("===============================");  
  System.out.println("b1="+ b1.toString());
  System.out.println("Bean2="+ this.toString()); 
  
  System.out.println("\n2. Displaying class names      ");
  System.out.println("===============================");  
  System.out.println("b1="+ b1.getClass().getName());
  System.out.println("Bean2="+ this.getClass().getName()); 
  
  System.out.println("\n3. Displaying information using Reflection API");
  System.out.println("==============================================");  
  System.out.println("b1="+ ReflectionUtil.getObjectInfoReflx(b1));
  System.out.println("b1="+ ReflectionUtil.getObjectInfoReflx(this));
  
  System.out.println("\n4. Displaying information using Bean Info API");
  System.out.println("==============================================");  
  System.out.println("b1="+ ReflectionUtil.getObjectInfoBean(b1));
  System.out.println("b1="+ ReflectionUtil.getObjectInfoBean(this));
  
  System.out.println("\n5. Displaying information using Both APIs");
  System.out.println("==============================================");  
  System.out.println("b1="+ ReflectionUtil.getObjectInfo(b1));
  System.out.println("b1="+ ReflectionUtil.getObjectInfo(this));
  
  return null;
 }
}


Notice:
  1. Bean1 is injected into Bean2 (line 15)
  2. When displaying b1 class name (line 29) the name of the proxy class is displayed.
  3. When displaying the fields using Reflection, (line 34) b1 fields are rather strange as it is a proxy.
  4. When displaying the fields using Bean Info (line 39), a field called targetInstance is the underlying object.
  5. With the new method getObjectInfo (line 44) that combines both API s>(Reflection and Bean) . we have solved the problem by means of using Reflection over the underlaying object when it is proxied.

ReflexionUtil.java

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package org.ximodante.jsf.provesalfred;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;

public class ReflectionUtil {

 /**
  * A class whose name contanins "$Proxy$", is a class injected and proxied by CDI
  * @param cls
  * @return
  */
 public static boolean isProxy(Class<?> cls) {
  if (cls.getSimpleName().contains("Proxy$")) return true;
  else return false;
 }

 // Returns the underlying object proxied by CDI
 public static Object getProxiedObject(Object obj) throws IntrospectionException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{
  BeanInfo beanInfo;
  Object value=null;
 
  beanInfo = Introspector.getBeanInfo(obj.getClass());
  PropertyDescriptor oProperty = Arrays.stream(beanInfo.getPropertyDescriptors())
   .filter(e -> e.getName().equalsIgnoreCase("targetInstance"))
   .findFirst().get();
  Method getter = oProperty.getReadMethod();
  value = getter.invoke(obj);
 
  return value;
 }

 // Gets information from a class bypassing proxies
 public static String getObjectInfo(Object obj){
  String info="";
 
  Object myObj=obj;
  Class<?> cls=myObj.getClass();
 
  try {
   //Obtain original class (if stored in a proxy) 
   if (isProxy(cls)) { 
    myObj=getProxiedObject(myObj);
    cls=myObj.getClass();
   } 
   info =  getObjectInfoReflx(myObj);
  
  } catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException | IntrospectionException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
  return info;

 }

 
 
 // Gets information from a class but cannot bypass proxies!!!!!
 public static String getObjectInfoReflx(Object obj) {
  String info="";
  int i=0;  
  try {
   
   info = info + "CLASS:" + obj.getClass().getName() + "\n";
   info = info + "--------------------------------------------------\n";
   for (Field f: obj.getClass().getDeclaredFields()){
    f.setAccessible(true);
   
    if (f!=null) {
    
     info= info + "  Field n." + i + "=" +  f.getName() + "  Type=" + f.getType();
     if (f.get(obj) != null) { 
      info= info + "  Value=" + f.get(obj).toString().trim(); 
     }
     i++;
     info=info + "\n";
    }            
   }    
 
  } catch (Exception e) {
   e.printStackTrace();
  } 
 
  return info;
 }
 
 /**
  * Retrieves information from an object using Bean API
  * @param obj
  * @return
  */
 public static String getObjectInfoBean(Object obj) {
  BeanInfo beanInfo;
  String info="";
  try {
   info = info + "CLASS:" + obj.getClass().getName() + "\n";
   info = info + "--------------------------------------------------\n";
   
  
   beanInfo = Introspector.getBeanInfo(obj.getClass());
   int i=0;
   for (PropertyDescriptor property : beanInfo.getPropertyDescriptors()) {
    String name = property.getName();
    Method getter = property.getReadMethod();
    Object value = getter.invoke(obj);
    String className=property.getPropertyType().getName();
    
    info= info + "  Field n." + i + "=" +  name + "  Type=" + value.getClass().getName();
    if (value != null) { 
     info= info + "  Value=" + value.toString().trim(); 
    }
    info=info + "\n";
    i++;
   } 
  } catch (Exception e) {
   e.printStackTrace();
  }
  return info;
 }
}

Notice:
  1. When a class is a proxy, its class name includes the string "Proxy$".
  2. Notice how field information is retrieved in Reflection and Bean APIs.
  3. How the field information is extracted taking into account if the class is proxied or not.

 The xhtml page is

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<html xmlns="http://www.w3.org/1999/xhtml" 
      xmlns:h="http://java.sun.com/jsf/html" 
      xmlns:f="http://java.sun.com/jsf/core" 
      xmlns:p="http://primefaces.org/ui">  
    <h:head>  
    </h:head>  
      
    <h:body>  
      <h:form>  
        <p:panel header="TEST CDI REFLECTION">    
    <h3>Reflection with CDI</h3>
         
       field1:<h:inputText value="#{bean1.field1}"/> <br />
       
       field2:<h:inputText value="#{bean2.field2}"/>
       
     </p:panel>
     <h:commandButton value="Go" action="#{bean2.go}"/>  
      </h:form>
    </h:body>  
</html>



Look the window


And look carefully the results

 
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HELLO!
1. Displaying fields from beans
===============================
b1=Bean1(field1=a)
Bean2=Bean2(b1=Bean1(field1=a), field2=33)

2. Displaying class names      
===============================
b1=org.ximodante.jsf.provesalfred.Bean1$Proxy$_$$_WeldClientProxy
Bean2=org.ximodante.jsf.provesalfred.Bean2

3. Displaying information using Reflection API
==============================================
b1=CLASS:org.ximodante.jsf.provesalfred.Bean1$Proxy$_$$_WeldClientProxy
--------------------------------------------------
  Field n.0=BEAN_ID_FIELD  Type=interface org.jboss.weld.serialization.spi.BeanIdentifier  Value=WELD%ManagedBean%STATIC_INSTANCE|/JSFv02_/WEB-INF/classes|org.ximodante.jsf.provesalfred.Bean1|null|false
  Field n.1=weld$$$53  Type=class java.lang.reflect.Method  Value=public abstract void org.jboss.weld.interceptor.proxy.LifecycleMixin.lifecycle_mixin_$$_preDestroy()
  Field n.2=weld$$$52  Type=class java.lang.reflect.Method  Value=public abstract void org.jboss.weld.interceptor.proxy.LifecycleMixin.lifecycle_mixin_$$_postConstruct()
  Field n.3=weld$$$55  Type=class java.lang.reflect.Method  Value=public abstract java.lang.Class org.jboss.weld.interceptor.util.proxy.TargetInstanceProxy.getTargetClass()
  Field n.4=weld$$$54  Type=class java.lang.reflect.Method  Value=public abstract java.lang.Object org.jboss.weld.interceptor.util.proxy.TargetInstanceProxy.getTargetInstance()
  Field n.5=methodHandler  Type=class org.jboss.weld.bean.proxy.ProxyMethodHandler  Value=org.jboss.weld.bean.proxy.ProxyMethodHandler@62ec8a98
  Field n.6=constructed  Type=boolean  Value=true

b1=CLASS:org.ximodante.jsf.provesalfred.Bean2
--------------------------------------------------
  Field n.0=serialVersionUID  Type=long  Value=1
  Field n.1=b1  Type=class org.ximodante.jsf.provesalfred.Bean1  Value=Bean1(field1=a)
  Field n.2=field2  Type=class java.lang.String  Value=33


4. Displaying information using Bean Info API
==============================================
b1=CLASS:org.ximodante.jsf.provesalfred.Bean1$Proxy$_$$_WeldClientProxy
--------------------------------------------------
  Field n.0=class  Type=java.lang.Class  Value=class org.ximodante.jsf.provesalfred.Bean1$Proxy$_$$_WeldClientProxy
  Field n.1=field1  Type=java.lang.String  Value=a
  Field n.2=handler  Type=org.jboss.weld.bean.proxy.ProxyMethodHandler  Value=org.jboss.weld.bean.proxy.ProxyMethodHandler@62ec8a98
  Field n.3=metadata  Type=org.jboss.weld.bean.proxy.ProxyMethodHandler  Value=org.jboss.weld.bean.proxy.ProxyMethodHandler@62ec8a98
  Field n.4=targetClass  Type=java.lang.Class  Value=class org.ximodante.jsf.provesalfred.Bean1
  Field n.5=targetInstance  Type=org.ximodante.jsf.provesalfred.Bean1  Value=Bean1(field1=a)

b1=CLASS:org.ximodante.jsf.provesalfred.Bean2
--------------------------------------------------
  Field n.0=b1  Type=org.ximodante.jsf.provesalfred.Bean1$Proxy$_$$_WeldClientProxy  Value=Bean1(field1=a)
  Field n.1=class  Type=java.lang.Class  Value=class org.ximodante.jsf.provesalfred.Bean2
  Field n.2=field2  Type=java.lang.String  Value=33


5. Displaying information using Both APIs
==============================================
b1=CLASS:org.ximodante.jsf.provesalfred.Bean1
--------------------------------------------------
  Field n.0=serialVersionUID  Type=long  Value=1
  Field n.1=field1  Type=class java.lang.String  Value=a

b1=CLASS:org.ximodante.jsf.provesalfred.Bean2
--------------------------------------------------
  Field n.0=serialVersionUID  Type=long  Value=1
  Field n.1=b1  Type=class org.ximodante.jsf.provesalfred.Bean1  Value=Bean1(field1=a)
  Field n.2=field2  Type=class java.lang.String  Value=33

Now we can use reflection on injected beans if we take into account these ideas.

 Have a nice programming session!

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