Injecting Objects by Using Producer Methods

Producer methods provide a way to inject objects that are not beans, objects whose values may vary at run time, and objects that require custom initialization.

For example, if you want to initialize a numeric value defined by a qualifier named @MaxNumber, you can define the value in a managed bean and then define a producer method, getMaxNumber, for it:

    private int maxNumber = 100;
    ...
    @Produces @MaxNumber int getMaxNumber() {
        return maxNumber;
    }

When you inject the object in another managed bean, the container automatically invokes the producer method, initializing the value to 100:

    @Inject @MaxNumber private int maxNumber;

If the value can vary at run time, the process is slightly different. For example, the following code defines a producer method that generates a random number defined by a qualifier called @Random:

    private java.util.Random random = 
        new java.util.Random( System.currentTimeMillis() );

    java.util.Random getRandom() {
        return random;
    }

    @Produces @Random int next() {
        return getRandom().nextInt(maxNumber);
    }

When you inject this object in another managed bean, you declare a contextual instance of the object:

    @Inject @Random Instance<Integer> randomInt;

You then call the get method of the Instance:

this.number = randomInt.get();