Java Spring bean with private constructor

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Is possible in Spring that class for bean doesn't have public constructor but only private ? Will this private constructor invoked when bean is created? Thanks.

Yes, Spring can invoke private constructors. If it finds a constructor with the right arguments, regardless of visibility, it will use reflection to set its constructor to be accessible.

Java Spring bean with private constructor, Is possible in Spring that class for bean doesn't have public constructor but only private ? Will this private constructor invoked when bean is  Yes, Spring can invoke private constructors. If it finds a constructor with the right arguments, regardless of visibility, it will use reflection to set its constructor to be accessible. share | improve this answer answered Aug 31 '11 at 8:48

You can always use a factory method to create beans rather than relying on a default constructor, from The IoC container: Instantiation using an instance factory method:

<!-- the factory bean, which contains a method called createInstance() -->
<bean id="serviceLocator" class="com.foo.DefaultServiceLocator">
  <!-- inject any dependencies required by this locator bean -->
</bean>

<!-- the bean to be created via the factory bean -->
<bean id="exampleBean"
      factory-bean="serviceLocator"
      factory-method="createInstance"/>

This has the advantage that you can use non-default constructors for your bean, and the dependencies for the factory method bean can be injected as well.

Java Spring bean with private constructor - Stack , Java-based configuration: Starting with Spring 3.0, many features provided by You can use the application context constructor to load bean definitions from all The object type returned from the invocation of the static factory method may be​  Yes, Spring can invoke private constructors. If it finds a constructor with the right arguments, regardless of visibility, it will use reflection to set its constructor to be accessible. share | improve this answer edited Aug 31 '11 at 9:13

Yes, Private constructors are invoked by spring. Consider my code:

Bean definition file:

<bean id="message" class="com.aa.testp.Message">
        <constructor-arg index="0" value="Hi Nice"/>
    </bean>

Bean class:

package com.aa.testp;

public class Message {

    private String message;

    private Message(String msg) {
       // You may add your log or print statements to check execution or invocation
        message = msg;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public void display() {
        System.out.println(" Hi " + message);
    }

}

The above code works fine. Hence, spring invoked the private constructor.

3. The IoC container - Project Metadata API Guide, are created with the configuration metadata that you supply to the container. Instantiate beans with a Constructor To instantiate spring beans using a constructor, you need to specify the bean class and set properties or constructor arguments after the object is constructed a shown in the following bean declaration.

You would normally have a static factory method in such beans, you can specify that method for spring to get an instance of that bean. See 3.3.1.3 here. This is the way it's recommended by Spring, rather than going against visibility restrictions.

How to Inject null and empty Values in Spring, Configuration metadata can be specified via XML, Java code or annotations. public class ExampleBean { // a private constructor private ExampleBean() { . Constructor injection is the process of injecting Spring dependencies into a Spring bean using the bean’s constructor. This differs from field injection where a dependency is simply injected using the @Autowired annotation directly on the field. Declaring a bean dependency via constructor injection usually looks as follows:

Yes ! Spring can access private constructor. It will works internally like below code.

       try{
    Class c= Class.forName("A"); // A - className
    Constructor c1[]=c.getDeclaredConstructors();
    c1[0].setAccessible(true);
    A a= (A)c1[0].newInstance();
    }
    catch (Exception e){
        e.printStackTrace();
    }

How to inject inner bean in spring?, In spring framework, IoC container can instantiate a bean by using-. A constructor​; A static factory method; An instance factory method  There's no way for Spring to know what ShoppingCart instance to use when instantiating CreateDatabaseAction if there is no managed bean of that type. I think that you should reconsider the design. For example send it as method parameter where it's actually used and remove it from the constructor.

Is Spring Bean Thread Safe?, Google Groups allows you to create and participate in online forums and email-​based groups with a rich experience for community conversations. 1. create a timeout factory, and use that as the constructor parameter. You can create a bean which implements FactoryBean, and it's job is to create other beans. So if you had something that generates salt's for encryption, you could have it return from getObject() a EncryptionSalt object.

Spring - Bean Definition, Private constructor is used if you do not want other classes to instantiate the object. Private constructors are used in singleton design pattern, factory method  How to write a spring bean with a constructor that contains a list? a spring bean that takes handlers as one of its arguments, i.e. is it possible to do this in

3.4 Dependencies - Project Metadata API Guide, This annotation allows Spring to resolve and inject collaborating beans into your bean. and Dependency Injection, followed by a simple demonstration using the Spring Framework Once annotation injection is enabled, autowiring can be used on properties, setters, and constructors. private FooFormatter fooFormatter;. Using Spring's Java Config, I need to acquire/instantiate a prototype-scoped bean with constructor arguments that are only obtainable at runtime. Consider the following code example (simplified for brevity):

Comments
  • How about giving it a try and then posting the results?
  • It is difficult - I don't have all source.
  • Could you please give me the reference to docs? Constructor has parameters, and in xml file to this arguments assigned values.
  • you mean if a bean has specifically something like private bean() { ... } spring can invoke that? How is that possible, that defies the whole purpose of "private".
  • Sorry, I'm probably wrong about it only being no-arg constructors. I'm just going by what I've noticed on my own projects. I can't say I've ever seen it in the Spring documentation anywhere. But this is the javadoc for the class that is responsible for doing the instantiation. static.springsource.org/spring/docs/3.0.x/javadoc-api/org/…
  • @Ashkan It is possible using reflection. In particular, the Spring BeanUtils class uses a class called ReflectionUtils to make the constructor accessible. See javadocs for Constructor.setAccessible().
  • @Kevin Stembridge you are correct, it is possible using Reflection.
  • interesting, but I cannot find factory. May be exists another way?
  • @Matthew: He appears to be retrofitting Spring around some fugly third-party code. That's just bound to be messy.
  • @Donal, no I didn't understand what he said in the comment.
  • strange, there are no static method, no public constructor but when I do debug - private constructor invoked! by sun.reflect.NativeConstructorAccessorImpl
  • Without specifics/code it won't be possible to comment any further!
  • I suppose you are wrong. There are no specific code - I see in debugger only standard sun/spring methods.
  • @Ashkan: I suspect you're getting the -1 votes because you're wrong. Spring can peek behind the curtain (unless there's a strict security manager in place and the Spring code isn't marked as trusted).
  • @Ashkan: It's very bad style to go against visibility restrictions. Don't do it! Or if you do, feel very bad about it. (Spring does it because it wants to split the definition of a bean from its configuration, but they're typically still closely linked. This question happens to be about the exceptional case where that's not true…)