Spring Autowiring only works with Interface

Question

I am quite new to spring framework and came across the following issue.

I have an interface ClassA, which is implemented by classed ClassA1

Answer 1

I tried multiple ways to fix this problem, but I got it working the following way.

@Autowired
private ClassA classA1;

@Autowired
private ClassA classA2;

In the application context, I defined the bean as below:

<bean id="classA1" class="com.abc.ClassA1" autowire="byName" />
<bean id="classA2" class="com.abc.ClassA2" autowire="byName" />

Answer 2

I have similar problem with Autowiring abstract service. You can use without any problem code like this:

@Autowired
@Qualifier("classA1")
private ClassA1 classA1;

@Autowired
@Qualifier("classA2")
private ClassA2 classA2;

This will be working only if you declare your bean like this

<bean id="class1" class="com.abc.ClassA1" />

Or like this

@Component("classA1")
public class ClassA1 {
...
}

Answer 3

From the little I've seen till now, it doesn't seem to be any restriction, regarding the type of class that one could mark as @Autowired.

Non related to the issue, but this article makes reference to the situation itself

Answer 4

For some reason your classes are proxied by Spring. There many reasons why this can happen. For example if you use JPA, or AOP the original class is proxied.

If a class implements an interface, proxy means Dynamic Proxy. So basically a new class is created in runtime that implements the interfaces but does not inherit from the original class. Therefore the autowiring to the original class doesn't work.

Answer 5

If your objects are proxied by JDK proxies, then they should be referred to by their interface. You can make proxies by concrete class using CGLIB (on the classpath) and proxy-target-class="true" in your aop configuration (in applicationContext.xml)

Answer 6

You could use the @Qualifier annotation:

@Autowired
@Qualifier("class1")
ClassA classA1;

@Autowired
@Qualifier("class2")
ClassA classA2;

Ref: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-autowired-annotation-qualifiers

or the @Resource annotation:

@Resource(name="class1")
ClassA classA1;

@Resource(name="class2")
ClassA classA2;

Ref: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-resource-annotation