Spring Dependency Injection object pool

Question

We have an Object which does some calculations in a spring boot container. Lets call it "Sheet". We need to instantiate - let's say 10 - sheets when the application is started. Every time we start a calculation we need one instance of that sheet to be accessed via DI to be run in an extra Thread.

Any idea if that is possible in Spring?

Can't you use some usual pool? Like https://commons.apache.org/proper/commons-pool/? — , Jun 06 '17 at 05:39
Create custom spring bean https://stackoverflow.com/a/15773000/6743203 — Jay Smith, Jun 06 '17 at 05:53

score 4 · Accepted Answer · answered Jun 06 '17 at 06:36

You can achieve this in the following way.. lets say that you have a Sheet class as follow. I have used java8 to compile the code.

Sheet.java

 @Component("sheet")
    @Scope(value = "prototype")
    public class Sheet {
        // Implementation goes here
    }

Now you need a second class SheetPool which holds 10 instances of Sheet

SheetPool.java

public class SheetPool {

    private List<Sheet> sheets;

    public List<Sheet> getSheets() {
        return sheets;
    }

    public Sheet getObject() {
        int index = ThreadLocalRandom.current().nextInt(sheets.size());
        return sheets.get(index);
    }

}

Note that SheetPool is not a Spring component. it is just a plain java class.

Now you need a third class which is a config class, which will take care of creating SpringPool object with 10 instance of Sheet

ApplicationConfig.java

@Configuration
public class ApplicationConfig {

@Autowired
ApplicationContext applicationContext;

@Bean
public SheetPool sheetPool() {
    SheetPool pool = new SheetPool();

    IntStream.range(0, 10).forEach(e -> {
        pool.getSheets().add((Sheet) applicationContext.getBean("sheet"));
    });

    return pool;
}

}

Now when the application starts SheetPool object will be create with 10 different instance of Sheet.. To access the Sheet object use the following code.

@Autowired
SheetPool  sheetPool;

Sheet sheetObj = sheetPool.getObject();

This answer is correct, but note that if you make `SheetPool` implement [`FactoryBean`](https://docs.spring.io/spring/docs/5.2.2.RELEASE/javadoc-api/org/springframework/beans/factory/FactoryBean.html), then you can simply inject `Sheet` directly, and it will be retrieved from the factory bean (i.e. pool). — James_D, Jan 04 '20 at 19:42

Spring Dependency Injection object pool

1 Answers1