Learning Spring / Java: How To Inject Spring Bean

Question

I am learning Spring and Java at the same time. I am working on my application context. Here is one of my beans:

package com.example.app.context;

@Configuration
public class ApplicationContextConfiguration {

    @Bean
    public ComboPooledDataSource comboPooledDataSource() {
        // ... setup pool here
        return pool;
    }
}

Now I want to use this bean:

package com.example.db.queries;

import javax.inject.Inject;

public class DatabaseQueries {

    @Inject private ComboPooledDataSource comboPooledDataSource;

    public static List<Records> getData() {
        Connection connection = comboPooledDataSource.getConnection();
        // ... create sql query and execute 
}

But I get this error at compile time:

[ERROR] non-static variable comboPooledDataSource cannot be referenced from a static context

How do I access this bean?

Thanks in advance, and please remember, I'm learning!

The error tells your everything. Your field is an instance field. Your method is static. — Sotirios Delimanolis, Aug 20 '13 at 20:13
Ok thanks Brian, can you please help me out figure out what this is about? — David Williams, Aug 20 '13 at 20:13
Simply searching for that error will being up numerous questions on SO, I've marked this as a duplicate of one of them. — Brian Roach, Aug 20 '13 at 20:13
@DavidWilliams Your method is static and trying to access a non static object. — Sotirios Delimanolis, Aug 20 '13 at 20:15
But just for the record, this is the right way to inject??????? — David Williams, Aug 20 '13 at 20:17
@DavidWilliams - Instead of using class for configuration, I prefer defining beans in XML file. — Sachin Thapa, Aug 20 '13 at 20:20
Hi Sachin, thanks, I appreciate that, however I am trying to move it out of xml due to some feedback in a code review :) — David Williams, Aug 20 '13 at 20:24
Though when I get here: `public class DatabaseQuery { @Inject private ComboPooledDataSource comboPooledDataSource; private Connection getConnection() { try { return comboPooledDataSource.getConnection(); } catch (SQLException e) { e.printStackTrace(); } return null; } ` its a null pointer exception. How do I get at this bean? — David Williams, Aug 20 '13 at 21:05

fischermatte · Accepted Answer · 2013-08-20T20:27:43.950

3

Your method getData() ist static. when working with Spring or in generally with Dependency Injection you use static methods much less than you might used to be. Make it non-static. When ever you need to to use your DatabaseQueries, you inject it again.

@Component
public class DatabaseQueries {

@Inject 
private ComboPooledDataSource comboPooledDataSource;

public List<Records> getData() {
    Connection connection = comboPooledDataSource.getConnection();
    // ... create sql query and execute 
}

And the usage:

@Component
public class AnotherBean{

    @Inject 
    private DatabaseQueries queries;

    public void doSomething {
        List<Records> data = queries.getData();
    }
}

edited Aug 20 '13 at 20:27

answered Aug 20 '13 at 20:19

fischermatte

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+1. I would like to add the fact that all beans created by Spring are by default singletons. – adarshr Aug 20 '13 at 20:19
2

@adarshr We have to be careful. They are singleton in the Spring context. – Sotirios Delimanolis Aug 20 '13 at 20:20
true, not the best sample. be careful the the datasource. – fischermatte Aug 20 '13 at 20:23
Speaking of contexts, @Sotirios, how would I get at this bean in a unit test? How would I init Spring context in a test? – David Williams Aug 20 '13 at 20:28
@DavidWilliams You're better off googling that. You can use `@ContextConfiguration` with a `SpringJUnit4RunnerClassRunner`. – Sotirios Delimanolis Aug 20 '13 at 20:29

UpAllNight · Answer 2 · 2013-08-20T20:21:22.230

1

This is more of a Java error than a Spring one.

You need to declare the method getData() as not static.

edited Aug 20 '13 at 20:21

answered Aug 20 '13 at 20:13

UpAllNight

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If OP declares `ComboPooledDataSource` as static, it becomes a Spring problem because `@Inject` won't work, as is. – Sotirios Delimanolis Aug 20 '13 at 20:16

Learning Spring / Java: How To Inject Spring Bean

2 Answers2