CODEWITHSUNDEEP
javagenericsspring
digiarnie
digiarnie

Reputation: 23455

Defining spring bean using a class with generic parameters

If I have a class that looks something like this:

public class MyClass<T extends Enum<T>> {
  public void setFoo(T[] foos) {
    ....
  }
}

How would I go about declaring this as a bean in my context xml so that I can set the Foo array assuming I know what T is going to be (in my example, let's say T is an enum with the values ONE and TWO)?

At the moment, having something like this is not enough to tell spring what the type T is:

<bean id="myClass" class="example.MyClass">
  <property name="foo">
    <list>
      <value>ONE</value>
      <value>TWO</value>
    </list>
  </property>
</bean>

Edit: Forgot the list tag.

Upvotes: 37

Views: 59996

Answers (3)

Rod McDonald
Rod McDonald

Reputation: 179

Consider working example.

<bean id="simpleInt" 
      class="org.nipr.gateway.service.transaction_assistant.GenericSimple">
    <constructor-arg>
        <!-- this can be any full path to a class -->
        <value>java.lang.Integer</value> 
    </constructor-arg>
</bean>

and 

<bean id="simpleString"  
      class="org.nipr.gateway.service.transaction_assistant.GenericSimple">
    <constructor-arg>
        <value>java.lang.String</value>
    </constructor-arg>
</bean>

Simple generic class:

public class GenericSimple<T> {
    private Class<T> type;
    public GenericSimple(Class<T> type) {
        this.type = type;
    }
    public T get( T t) {
        return t;
    }
}

And finally, the test method (using factory):

public void testGeneric(){
    Factory factory = new Factory(new String[]{"config/beanForGenericTest.xml"});

    GenericSimple<Integer> simpleInt 
        = (GenericSimple<Integer>)factory.getClass("simpleInt");
    System.out.println(simpleInt.get(Integer.valueOf(100)));
    Assert.assertTrue(simpleInt.get(Integer.valueOf(100)).equals(100));

    GenericSimple<String> simpleString = 
        (GenericSimple<String>)factory.getClass("simpleString");
    System.out.println(simpleString.get(new String("Rockets go fast.")));
    Assert.assertTrue(simpleString.get("Rockets go fast.")
        .equals("Rockets go fast."));
}

Upvotes: 17

Arne Burmeister
Arne Burmeister

Reputation: 20614

Spring has no generic support for that case, but the compiler just creates a class cast in this case. So the right solution is:

<bean id="myClass" class="example.MyClass">
  <property name="foo">
    <list value-type="example.MyEnumType">
      <value>ONE</value>
      <value>TWO</value>
    </list>
  </property>
</bean>

Upvotes: 31

cletus
cletus

Reputation: 625387

<bean id="myClass" class="example.MyClass">
  <property name="foo">
    <list>
      <value>ONE</value>
      <value>TWO</value>
    </list>
  </property>
</bean>

Alternatively, you can define a custom editor.

Upvotes: 1

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