Spring Boot - 环境@Autowired抛出NullPointerException

Question

我使用Spring Boot 0.5.0.M5进行项目设置.

在我尝试的其中一个配置文件中,@Autowire Environment但是失败了NullPointerException.

这是我到目前为止所拥有的:

Application.java

@EnableAutoConfiguration
@Configuration
@ComponentScan
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

JpaConfig.java我想去的地方@Autowire Environment

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(basePackages = "com.ui.persistence.repository")
public class JpaConfig {
    private static final String DATABASE_DRIVER = "db.driver";
    private static final String DATABASE_PASSWORD = "db.password";
    private static final String DATABASE_URL = "db.url";
    private static final String DATABASE_USERNAME = "db.username";
    private static final String HIBERNATE_DIALECT = "hibernate.dialect";
    private static final String HIBERNATE_SHOW_SQL = "hibernate.show_sql";
    private static final String ENTITYMANAGER_PACKAGES_TO_SCAN 
        = "entitymanager.packages.to.scan";

    @Autowired
    private Environment env;

    @Bean
    public DataSource dataSource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(env.getProperty(DATABASE_DRIVER));
        dataSource.setUrl(env.getProperty(DATABASE_URL));
        dataSource.setUsername(env.getProperty(DATABASE_USERNAME));
        dataSource.setPassword(env.getProperty(DATABASE_PASSWORD));
        return dataSource;
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
        LocalContainerEntityManagerFactoryBean entityManagerFactoryBean 
                = new LocalContainerEntityManagerFactoryBean();
        entityManagerFactoryBean.setDataSource(dataSource());
        entityManagerFactoryBean.setPersistenceProviderClass(
                HibernatePersistence.class);
        entityManagerFactoryBean.setPackagesToScan(
                env.getProperty(ENTITYMANAGER_PACKAGES_TO_SCAN));
        entityManagerFactoryBean.setJpaProperties(hibernateProperties());
        return entityManagerFactoryBean;
    }
}

我正在尝试加载属性文件中配置的数据库属性.但是,Environment没有注入,代码失败了NullPointerException.我在XML文件中没有任何配置.

对于我以PropertySourcesPlaceholderConfigurer这种方式配置的属性文件:

@Configuration
@PropertySource("classpath:database.properties")
public class PropertyConfig {
    @Bean
    public static PropertySourcesPlaceholderConfigurer propertyPlaceHolderConfigurer() {
        return new PropertySourcesPlaceholderConfigurer();
    }
}

我试图交换@Autowired,@Resource并且@Inject但至今没有奏效.非常感谢任何帮助.谢谢.

Answer 1

虽然您的具体问题已经解决,但是如何避免EnvironmentSpring的自动装配发生得太晚.

诀窍是实施org.springframework.context.EnvironmentAware; 然后Spring将环境​​传递给setEnvironment()方法.这适用于Spring 3.1.

一个例子:

@Configuration
@PropertySource("classpath:myProperties.properties")
public class MyConfiguration implements EnvironmentAware {

    private Environment environment;

    @Override
    public void setEnvironment(final Environment environment) {
        this.environment = environment;
    }

    public void myMethod() {
        final String myPropertyValue = environment.getProperty("myProperty");
        // ...
    }

}

这并不像@Autowired或那样优雅@Value,但在某些情况下它可以解决方法.

Answer 2

我在从 Spring Boot 应用程序中的 application.properties 文件中读取属性时遇到了类似的问题。为了找出问题并使其发挥作用，我付出了很多努力。最后我完成了。这是我的 Constants 类，它将从属性文件中读取属性值。我希望它会对某人有所帮助。

import org.springframework.context.EnvironmentAware;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.core.env.Environment;

@Configuration
@PropertySource("classpath:application.properties")
public class Constants implements EnvironmentAware {

static Environment environment;

@Override
public void setEnvironment(Environment environment) {
    Constants.environment = environment;
}

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

public static String getActiveMQHost() {
    System.out.println(environment.getProperty("spring.activemq.broker-host"));
    return environment.getProperty("spring.activemq.broker-host");
}

public static String getActiveMQPort() {
    System.out.println(environment.getProperty("spring.activemq.broker-port"));
    return environment.getProperty("spring.activemq.broker-port");
}

public static String getActiveMQUser() {
    System.out.println(environment.getProperty("spring.activemq.user"));
    return environment.getProperty("spring.activemq.user");
}

public static String getActiveMQPassword() {
    System.out.println(environment.getProperty("spring.activemq.password"));
    return environment.getProperty("spring.activemq.password");
}

}

这些是我的 application.properties 中声明的属性键，

spring.activemq.broker-host
spring.activemq.broker-port
spring.activemq.user
spring.activemq.password

Answer 3

我相信Spring和它们存在一些生命周期问题EntityManagerFactory,你可能会对那些问题(在4.0.0.RC1中修复) - 如果你的@Configuration类超级实例化,它可能没有资格进行自动装配.您可以从日志输出中判断出是否是这种情况.

只是出于兴趣,你知道的功能由您提供的JpaConfig,并PropertyConfig已经presetn开箱即用的,如果你使用@EnableAutoConfiguration(只要您@ComponentScan在您的存储库中定义的包)？有关示例,请参阅Spring Boot中的JPA示例.

Answer 4

我在 Spring Batch 上遇到了同样的问题。编写器无法自动装配 Environment 类，因为 Configuration 类较早实例化。所以我创建了一种单例（旧方式）来实例化环境，我每次都可以访问它。

我做了这个实现：

@Configuration
@PropertySource(value = { "classpath:kid-batch.properties" }, ignoreResourceNotFound = false)
public class BatchConfiguration implements EnvironmentAware {

private static Environment env;

public static String getProperty(String key) {
    return env.getProperty(key);
}

@Override
public void setEnvironment(Environment env) {
    BatchConfiguration.env = env;
}

}

它有效