Constructor question

[nimo22]

According weld documentation (chapter: 1.2),
I have not use a constructor with no paramer, when using constructor injection:

But wait! TextTranslator does not have a constructor with no parameters! Is it still a bean? If you remember,
a class that does not have a constructor with no parameters can still be a bean if it has a constructor annotated
@Inject.

Compiling this:

@SessionScoped @Named
public class MyBean{
        
   @PersistenceContext EntityManager entityManager;

    OtherBean ob;
        
// I do not use the Constructor with no parameters
//      public MyBean(){}  
        
        @Inject
        public MyBean(OtherBean ob){
                
                this.ob= ob;

        }
        
        public OtherBean getOb() {return ob;}
        public void setOb(OtherBean ob) {this.ob= ob;}
}

leads to the following error:

ERROR: Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.0.2:testCompile (default-testCompile) on project Project: Compilation failure
...\Project\MyBean.java:[28,26] cannot find symbol
symbol  : constructor MyBean()
location: class com.MyBean

I have to use this, in order to compile the code successfully:

@SessionScoped @Named
public class MyBean{

@PersistenceContext EntityManager entityManager;

        OtherBean ob;
        
// I have to use this Constructor additionally to the injected Constructor
        public MyBean(){}  
        
        @Inject
        public MyBean(OtherBean ob){
                
                this.ob= ob;

        }
        
        public OtherBean getOb() {return ob;}
        public void setOb(OtherBean ob) {this.ob= ob;}
}

So do I misunderstood that ?:

If you remember, a class that does not have a constructor with no parameters can still be a bean if it has a constructor annotated.

My class has not a constructor with no parameters, but it has a injected constructor (with parameters).

[mbogoevici]

Hm, this is a compilation error. Are you sure that you're not invoking the no-arg constructor explicitely from anywhere in your code?

Apart from that, and completely unrelated to the compilation error - and I stress that :), you may need a no-arg constructor anyway, since your bean is normal-scoped (session-scoped) - and the framework will need to be able to create a proxy for it - read chapter 5.4 of the CDI specification for details. But, even then, this would show up at deployment time and not during compilation.

[asiandub]

I can confirm that the above code compiles :-)

As Marius suggests:

1. a compilation error should always be unrelated to any Weld issued


2. a deployment error will be thrown by the container because MyBean is not proxyable

org.jboss.weld.exceptions.UnproxyableResolutionException: 
WELD-001400 Normal scoped bean org.jboss.weld.bean-flat-ManagedBean-class ...MyBean is not proxyable
     at org.jboss.weld.bootstrap.Validator.validateBean(Validator.java:127)

The example from the Weld-reference which you are quoting is not annotated, and therefore @dependent-scoped, which does not require the bean to be proxyable...

public class TextTranslator {
private SentenceParser sentenceParser;
private Translator sentenceTranslator;

[nimo22]

Hello Marius,

yes, you are right. I had overseen that I invoked the no-arg constructor explicitely from my Test-Code.

So to sum up:

When injecting constructor, should I use this:

Version 1:

        public MyBean(){}  
        
        @Inject
        public MyBean(OtherBean ob){
                
                this.ob= ob;

        }

or that:

Version 2:

 public MyBean(){}  
        
        // Normally (without CDI), I also need the non-arg constructor.
        public MyBean(){}

        @Inject
        public MyBean(OtherBean ob){
                
                this.ob= ob;

        }

In CDI, both versions work. Which version should I use? Does it make a difference?

[nimo22]

you may need a no-arg constructor anyway, since your bean is normal-scoped (session-scoped)

Okay, so I need to use version 2. However, using version 1 does not return a deployment error.