Top 6 Spring wiring via JavaConfig [i.e. @Configuration ] examples

Spring Java Configuration (i.e. JavaConfig) provides a pure-Java means of configuring the Spring IoC container. This is gaining popularity as it

gives complete control over instantiation and dependency injection.
gives type safety & compile-time check
supports refactorable configuration & supported by IDEs

Here are some industrial strength wiring examples.

#1, #2, #3. Wiring datasource, entity manager, and transactionManager

package com.jpa.tutorial.config;

import static org.hibernate.cfg.Environment.DIALECT;
import static org.hibernate.cfg.Environment.SHOW_SQL;

import java.util.Properties;

import javax.inject.Inject;
import javax.sql.DataSource;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;
import org.springframework.jdbc.datasource.lookup.JndiDataSourceLookup;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.PlatformTransactionManager;

@Configuration
@EnableAspectJAutoProxy
@ComponentScan(basePackages = "com.jpa.tutorial.domain") 
@PropertySource("classpath:my-orm.properties")
public class MyDomainConfiguration {

    @Inject
    private Environment environment;

    @Bean
    public DataSource dataSource() {
        final JndiDataSourceLookup jndiLookup = new JndiDataSourceLookup();
        final String dataSourceJndi = environment.getRequiredProperty("myapp.domain.datasource.jndi");
        return jndiLookup.getDataSource(dataSourceJndi);
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
        final LocalContainerEntityManagerFactoryBean entityManager = new LocalContainerEntityManagerFactoryBean();

        entityManager.setPersistenceUnitName("myapp-persistence-unit");
        entityManager.setDataSource(dataSource());
        entityManager.setPersistenceXmlLocation("classpath:META-INF/persistence-jpa.xml");
        entityManager.setPackagesToScan("com.jpa.tutorial.**.entity");

        final HibernateJpaVendorAdapter hibernateAdapter = new HibernateJpaVendorAdapter();
        entityManager.setJpaVendorAdapter(hibernateAdapter);

        final Properties properties = myappCommonsDomainProperties();
        entityManager.setJpaProperties(properties);
        entityManager.afterPropertiesSet();
        return entityManager;
    }

    @Bean
    public Properties myappCommonsDomainProperties() {
        final Properties properties = new Properties();
        properties.put(DIALECT, environment.getRequiredProperty(DIALECT));

        // debugging properties
        properties.put(SHOW_SQL, environment.getRequiredProperty(SHOW_SQL));
        return properties;
    }

    @Bean
    public PlatformTransactionManager transactionManager() {
        final PlatformTransactionManager transactionManager;

        final JpaTransactionManager jpaTransactionManager = new JpaTransactionManager();
        jpaTransactionManager.setEntityManagerFactory(entityManagerFactory().getObject());
        jpaTransactionManager.setDataSource(dataSource());
        transactionManager = jpaTransactionManager;
        return transactionManager;
    }
}

package com.jpa.tutorial.config;

import static org.hibernate.cfg.Environment.DIALECT;

import static org.hibernate.cfg.Environment.SHOW_SQL;

import java.util.Properties;

import javax.inject.Inject;

import javax.sql.DataSource;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.ComponentScan;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.EnableAspectJAutoProxy;

import org.springframework.context.annotation.PropertySource;

import org.springframework.core.env.Environment;

import org.springframework.jdbc.datasource.lookup.JndiDataSourceLookup;

import org.springframework.orm.jpa.JpaTransactionManager;

import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;

import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;

import org.springframework.transaction.PlatformTransactionManager;

@Configuration

@EnableAspectJAutoProxy

@ComponentScan(basePackages = "com.jpa.tutorial.domain")

@PropertySource("classpath:my-orm.properties")

public class MyDomainConfiguration {

@Inject

private Environment environment;

@Bean

public DataSource dataSource() {

final JndiDataSourceLookup jndiLookup = new JndiDataSourceLookup();

final String dataSourceJndi = environment.getRequiredProperty("myapp.domain.datasource.jndi");

return jndiLookup.getDataSource(dataSourceJndi);

}

@Bean

public LocalContainerEntityManagerFactoryBean entityManagerFactory() {

final LocalContainerEntityManagerFactoryBean entityManager = new LocalContainerEntityManagerFactoryBean();

entityManager.setPersistenceUnitName("myapp-persistence-unit");

entityManager.setDataSource(dataSource());

entityManager.setPersistenceXmlLocation("classpath:META-INF/persistence-jpa.xml");

entityManager.setPackagesToScan("com.jpa.tutorial.**.entity");

final HibernateJpaVendorAdapter hibernateAdapter = new HibernateJpaVendorAdapter();

entityManager.setJpaVendorAdapter(hibernateAdapter);

final Properties properties = myappCommonsDomainProperties();

entityManager.setJpaProperties(properties);

entityManager.afterPropertiesSet();

return entityManager;

}

@Bean

public Properties myappCommonsDomainProperties() {

final Properties properties = new Properties();

properties.put(DIALECT, environment.getRequiredProperty(DIALECT));

// debugging properties

properties.put(SHOW_SQL, environment.getRequiredProperty(SHOW_SQL));

return properties;

}

@Bean

public PlatformTransactionManager transactionManager() {

final PlatformTransactionManager transactionManager;

final JpaTransactionManager jpaTransactionManager = new JpaTransactionManager();

jpaTransactionManager.setEntityManagerFactory(entityManagerFactory().getObject());

jpaTransactionManager.setDataSource(dataSource());

transactionManager = jpaTransactionManager;

return transactionManager;

}

#4. Unit tests require wiring up actual datasource with mock in memory datasource

package com.jpa.tutorial.config;

import javax.sql.DataSource;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder;
import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType;

@Configuration
@Import(MyDomainConfiguration.class)
public class MyAppCommonsDomainTestConfiguration {

    @Bean
    public DataSource dataSource() {
        final EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder();
        builder.setType(EmbeddedDatabaseType.HSQL);
        builder.addScript("classpath:hsqldb-oracle.sql");
        builder.addDefaultScripts();//adds schema.sql
        return builder.build();
    }
}

package com.jpa.tutorial.config;

import javax.sql.DataSource;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Import;

import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder;

import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType;

@Configuration

@Import(MyDomainConfiguration.class)

public class MyAppCommonsDomainTestConfiguration {

@Bean

public DataSource dataSource() {

final EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder();

builder.setType(EmbeddedDatabaseType.HSQL);

builder.addScript("classpath:hsqldb-oracle.sql");

builder.addDefaultScripts();//adds schema.sql

return builder.build();

}

#5, #6. Wiring RESTful templates and JAXB marshaller

package com.mytutorial.configuration;

import static javax.xml.bind.Marshaller.JAXB_FORMATTED_OUTPUT;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.oxm.jaxb.Jaxb2Marshaller;
import org.springframework.transaction.annotation.EnableTransactionManagement;
import org.springframework.web.client.ResponseErrorHandler;
import org.springframework.web.client.RestTemplate;
import com.google.common.collect.ImmutableMap;
import com.mytutorial.RestTemplateExceptionTranslator;

@Configuration
@EnableTransactionManagement
@ComponentScan("com.mytutorial")
public class MyAppEnablerServiceConfiguration {
   
    @Bean
    public Jaxb2Marshaller jaxb2Marshaller() {
        final Jaxb2Marshaller marshaller = new Jaxb2Marshaller();
        marshaller.setPackagesToScan(
            "com.mytutorial.schema.v1.dto",
            "com.mytutorial.v1"
        );
        marshaller.setMarshallerProperties(
            ImmutableMap.<String, Object>of(JAXB_FORMATTED_OUTPUT, Boolean.TRUE));
        return marshaller;
    }

   
    @Bean
    public RestTemplate restTemplate() {
        final RestTemplate restTemplate = new RestTemplate();
        restTemplate.setErrorHandler(restTemplateExceptionTranslator());
        return restTemplate;
    }

 
    @Bean
    public ResponseErrorHandler restTemplateExceptionTranslator() {
        return new RestTemplateExceptionTranslator(); // custom handler
    }
}

package com.mytutorial.configuration;

import static javax.xml.bind.Marshaller.JAXB_FORMATTED_OUTPUT;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.ComponentScan;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Import;

import org.springframework.oxm.jaxb.Jaxb2Marshaller;

import org.springframework.transaction.annotation.EnableTransactionManagement;

import org.springframework.web.client.ResponseErrorHandler;

import org.springframework.web.client.RestTemplate;

import com.google.common.collect.ImmutableMap;

import com.mytutorial.RestTemplateExceptionTranslator;

@Configuration

@EnableTransactionManagement

@ComponentScan("com.mytutorial")

public class MyAppEnablerServiceConfiguration {

@Bean

public Jaxb2Marshaller jaxb2Marshaller() {

final Jaxb2Marshaller marshaller = new Jaxb2Marshaller();

marshaller.setPackagesToScan(

"com.mytutorial.schema.v1.dto",

"com.mytutorial.v1"

);

marshaller.setMarshallerProperties(

ImmutableMap.<String, Object>of(JAXB_FORMATTED_OUTPUT, Boolean.TRUE));

return marshaller;

}

@Bean

public RestTemplate restTemplate() {

final RestTemplate restTemplate = new RestTemplate();

restTemplate.setErrorHandler(restTemplateExceptionTranslator());

return restTemplate;

}

@Bean

public ResponseErrorHandler restTemplateExceptionTranslator() {

return new RestTemplateExceptionTranslator(); // custom handler

}

#7 wiring properties

@Bean
public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
     return new PropertySourcesPlaceholderConfigurer();
}

@Bean

public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {

return new PropertySourcesPlaceholderConfigurer();

}

@PropertySource({ "classpath:myapp-${envTarget:dev}.properties" })
...

@PropertySource({ "classpath:myapp-${envTarget:dev}.properties" })

...

Alternatively,

@Bean
public static PropertyPlaceholderConfigurer properties(){
  PropertyPlaceholderConfigurer ppc = new PropertyPlaceholderConfigurer();
  Resource[] resources = new ClassPathResource[ ]
    { new ClassPathResource( "myapp-dev}.properties" ) };
  ppc.setLocations( resources );
  ppc.setIgnoreUnresolvablePlaceholders( true );
  return ppc;
}

@Bean

public static PropertyPlaceholderConfigurer properties(){

PropertyPlaceholderConfigurer ppc = new PropertyPlaceholderConfigurer();

Resource[] resources = new ClassPathResource[ ]

{ new ClassPathResource( "myapp-dev}.properties" ) };

ppc.setLocations( resources );

ppc.setIgnoreUnresolvablePlaceholders( true );

return ppc;

}

and then,

@Value( "${ws.url:aDefaultUrl}" )
private String restWsUrl;

@Value( "${ws.url:aDefaultUrl}" )

private String restWsUrl;

@Autowired
private Environment env;
...env.getProperty("ws.url"));

@Autowired

private Environment env;

...env.getProperty("ws.url"));

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Top 6 Spring wiring via JavaConfig [i.e. @Configuration ] examples

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