Spring 3 @Component and static factory method

Question

If I'm writing a static factory method to create objects, how do I use the '@Component' annotation for that factory class and indicate (with some annotation) the static factory method which should be called to create beans of that class? Following is the pseudo-code of what I mean:

@Component
class MyStaticFactory
{
    @<some-annotation>
    public static MyObject getObject()
    {
        // code to create/return the instance
    }
}

Answer 1

I am afraid you can't do this currently. However it is pretty simple with Java Configuration:

@Configuration
public class Conf {

    @Bean
    public MyObject myObject() {
        return MyStaticFactory.getObject()
    }

}

In this case MyStaticFactory does not require any Spring annotations. And of course you can use good ol' XML instead.

Answer 2

You need to use the spring interface FactoryBean .

Interface to be implemented by objects used within a BeanFactory which are themselves factories. If a bean implements this interface, it is used as a factory for an object to expose, not directly as a bean instance that will be exposed itself.

Implement the interface and declare a bean for it. For example :

@Component
class MyStaticFactoryFactoryBean implements FactoryBean<MyStaticFactory>
{
    public MyStaticFactory getObject()
        MyStaticFactory.getObject();
    }
    public Class<?> getObjectType() {
        return MyStaticFactory.class;
    }
    public boolean isSingleton() {
        return true;
    }
}

Through @Component and component scanning, this class will be discovered. Spring will detect that it is a FactoryBean and expose the object you return from getObject as a bean (singleton if you specify it).

Alternatively, you can provide a @Bean or <bean> declaration for this FactoryBean class.

Answer 3

Spring boot:static factory method:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;

enum ParsersConst {
    bofa, jpm, wellsforgo
}

interface Parser {
    String readFromFile(String file);
}

class JPM implements Parser {
    @Override
    public String readFromFile(String file) {
        System.out.println("From JPM Parser");
        return "JPM";
    }
}

class Bofa implements Parser {
    @Override
    public String readFromFile(String file) {
        System.out.println("From Bofa Parser");
        return "BOFA";
    }
}

class WellsForgo implements Parser {
    @Override
    public String readFromFile(String file) {
        System.out.println("From Wellsforgo Parser");
        return "WellsForgo";
    }
}


class ParserCreator {

    public static Parser createParser(ParsersConst parsConst) {
        if (ParsersConst.bofa.equals(parsConst)) {
            return new Bofa();
        } else if (ParsersConst.jpm.equals(parsConst)) {
            return new JPM();
        } else if (ParsersConst.wellsforgo.equals(parsConst)) {
            return new WellsForgo();
        }
        throw new IllegalArgumentException("Unknown Parser");
    }
}
@Configuration
class ParserConfig{
    @Bean
    public Parser bofa() {
        return ParserCreator.createParser(ParsersConst.bofa);
    }
    @Bean
    public Parser wellsforgo() {
        return ParserCreator.createParser(ParsersConst.wellsforgo);
    }
    @Bean
    public Parser jpm() {
        return ParserCreator.createParser(ParsersConst.jpm);
    }
}

@Component
public class StaticFacotryDemo implements CommandLineRunner{
    @Autowired
    private ApplicationContext context;
    @Override
    public void run(String... args) throws Exception {

            Parser parser = (Parser) context.getBean(ParsersConst.jpm.toString());
            System.out.println(parser);
            System.out.println(parser.readFromFile("jan_stmt.pdf"));

    }

}

Answer 4

Bean:

 public class MyObject {

        private String a;

        public MyObject(String a) {
            this.a = a;
        }

        @Override
        public String toString() {
            return a;
        }
    }

FactoryBean:

@Component
public class MyStaticFactory implements FactoryBean<MyObject> {


    @Override
    public MyObject getObject() throws Exception {
        return new MyObject("StaticFactory");
    }

    @Override
    public Class<?> getObjectType() {
        return MyObject.class;
    }

    @Override
    public boolean isSingleton() {
        return true;
    }

}

Use:

@Component
public class SomeClass{


    @Autowired
    MyObject myObject;
}