使用Spring注釋讀取文件屬性

Question

我正在嘗試學習如何使用spring讀取屬性文件。 在互聯網搜索后，我發現我可以使用@value和@PropertySource注釋來實現這一點。 我創建了一個具有以下結構和類代碼的項目：

項目結構：

AppConfigMongoDB.java實現：

package com.mongodb.properties;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.PropertySource;


@PropertySource("classpath:config/config.properties")
public class AppConfigMongoDB {

@Value("#{mongodb.url}")
private String mongodbUrl;


@Value("#{mongodb.db}")
private String defaultDb;

public String getMongoDb()
{
    return defaultDb;
}

public String getMongoDbUrl()
{
    return mongodbUrl;
}
}

SpringConfiguration.java實現：

 package com.mongodb.properties;

 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;

 @Configuration
 public class SpringConfiguration {
 @Bean
 public AppConfigMongoDB getAppConfigMongoDB(){
        return new AppConfigMongoDB();
  }
 }

Main.java

package com.mongodb.properties;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Main {

public static void main(String[] args) {
    ApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfiguration.class);
    AppConfigMongoDB mongo = applicationContext.getBean(AppConfigMongoDB.class);
    System.out.println("db= "+mongo.getMongoDb());
    System.out.println("URL= "+mongo.getMongoDbUrl());
  }
}

我正在讀取的屬性文件名為config.properties，它包含以下行：

mongodb.url=1.2.3.4
mongodb.db=dataBase

我測試了這個小項目，我得到了一個包含以下異常的堆棧跟蹤：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'getAppConfigMongoDB': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private java.lang.String com.mongodb.properties.AppConfigMongoDB.mongodbUrl; nested exception is org.springframework.beans.factory.BeanExpressionException: Expression parsing failed; nested exception is org.springframework.expression.spel.SpelEvaluationException: EL1008E:(pos 0): Property or field 'mongodb' cannot be found on object of type 'org.springframework.beans.factory.config.BeanExpressionContext' - maybe not public?
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1202)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:84)
at com.mongodb.properties.Main.main(Main.java:9)

 Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1008E:(pos 0): Property or field 'mongodb' cannot be found on object of type 'org.springframework.beans.factory.config.BeanExpressionContext' - maybe not public?
at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:226)
at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:93)
at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:81)
at org.springframework.expression.spel.ast.CompoundExpression.getValueRef(CompoundExpression.java:51)
at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:87)
at org.springframework.expression.spel.ast.SpelNodeImpl.getValue(SpelNodeImpl.java:120)
at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:242)
at org.springframework.context.expression.StandardBeanExpressionResolver.evaluate(StandardBeanExpressionResolver.java:161)
... 18 more

這是Spring調用bean的問題嗎？ 或者可能是屬性文件路徑或其他問題？

Answer 1

我可以在代碼中看到幾個問題。

1）你的價值持有者應該是${mogodb.url} ，而不是#{mongodb.url} 。 “＃”具有不同的含義（參見Spring Expressions ）。

2）您將需要一個PropertySourcesPlaceholderConfigurer bean來執行值的注入

3）你遲早會有一些豆子漂浮在周圍，我會用@ComponentScan來讓上下文知道這些，而你不必一個一個地提到它們

4）如果使用ComponentScan獲取bean，則必須提供一次AppConfigMongoDB bean

在完成所有這些后，我最終得到了這些類：

Main.java

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Main {

public static void main(String[] args) {
    ApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfiguration.class);
    AppConfigMongoDB mongo = applicationContext.getBean(AppConfigMongoDB.class);
    System.out.println("db= "+mongo.getMongoDb());
    System.out.println("URL= "+mongo.getMongoDbUrl());
  }
}

SpringConfiguration.java

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;

@Configuration
@ComponentScan
public class SpringConfiguration {

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

AppConfigMongoDB.java

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;

@Configuration
@PropertySource("classpath:config/config.properties")
public class AppConfigMongoDB {

  @Value("${mongodb.url}")
  private String mongodbUrl;

  @Value("${mongodb.db}")
  private String defaultDb;

  public String getMongoDb() {
    return defaultDb;
  }

  public String getMongoDbUrl() {
    return mongodbUrl;
  }
}

Answer 2

@Ian Sparkes給出了很好的回復。 在這里添加一些輸入。 配置PropertySourcesPlaceholderConfigurer不是必需的。 我可以從我的屬性文件中獲取值，並將其設置為我的主要Configuration類的字段變量，而不是它。

還有另一種方法可以在屬性文件中獲取鍵的值。 使用org.springframework.core.env.Environment類。 此類自動加載類路徑中的屬性文件中的所有鍵值對。

示例：

 @Configuration @ComponentScan(basePackages="com.easy.buy") @PropertySource({"classpath:config.properties","classpath:props/db-${env}-config.properties", "classpath:props/app-${env}-config.properties"}) public class CatalogServiceConfiguration { Logger logger = LoggerFactory.getLogger(CatalogServiceConfiguration.class); //This object loads & holds all the properties in it as key-pair values @Autowired private Environment env; /** * Instantiate the DataSource bean & initialize it with db connection properties * @return */ @Bean(name="basicDataSource") public BasicDataSource basicDataSource() { String dbUrl = env.getProperty("db.url"); String dbUser = env.getProperty("db.user"); String dbPwd = env.getProperty("db.pwd"); String driver = env.getProperty("db.driver"); logger.info("Initializing CatalogServiceConfiguration"); logger.info("dbUrl=" + dbUrl); BasicDataSource ds = new BasicDataSource(); ds.setDriverClassName(driver); ds.setUrl(dbUrl); ds.setUsername(dbUser); ds.setPassword(dbPwd); return ds; } }