使用Spring注释读取文件属性 [英] Read file properties using Spring annotations

问题描述

我正在尝试学习如何使用spring读取属性文件.经过互联网搜索后，我发现可以使用@value和@PropertySource批注来实现.我创建了一个具有以下结构和类代码的项目:

I'm trying to learn how to read properties file using spring. After an internet searching I found that I can use @value and @PropertySource annotations to achieve that. I created a project which has the following structure and classes codes:

项目的结构:

AppConfigMongoDB.java实现:

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实现:

 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());
  }
}

我正在从config.properties中读取的属性文件，其中包含以下几行:

The properties file that I'm reading from called config.properties, it contains the following lines:

mongodb.url=1.2.3.4
mongodb.db=dataBase

我测试了这个小项目，并得到了一个包含以下异常的堆栈跟踪:

I tested this small project and I got a stack trace that contains the following exception:

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

Spring调用bean是一个问题吗?也许这是属性文件路径或其他问题的问题?

Is it a problem of Spring calling beans? Or maybe is it a problem of properties file path or something else?

推荐答案

我可以在代码中看到几个问题.

I can see several issues in the code.

1)您的值占位符的格式应为${mogodb.url}，而不是#{mongodb.url}. #"具有不同的含义(请参见 Spring表达式).

1) Your place holders for values should be in the form ${mogodb.url}, not #{mongodb.url}. The "#" has a different meaning (See Spring Expressions).

2)您将需要一个PropertySourcesPlaceholderConfigurer bean来注入值

2) You are going to need a PropertySourcesPlaceholderConfigurer bean to do the injection of the values

3)迟早会有很多Bean浮动，在这种情况下，我将使用@ComponentScan来使上下文知道这些Bean，而无需您一一提及它们

3) Sooner or later you are going to have a number of Beans floating around, and in I would use @ComponentScan to allow the context to know these without you having to mention them one by one

4)如果使用ComponentScan获取bean，则必须一次提供AppConfigMongoDB bean

4) If you use ComponentScan to get the beans, you are going to have to provide AppConfigMongoDB bean once

完成所有这些操作后，我最终得到了这些课程:

I end up with these classes after doing all that:

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;
  }
}

这篇关于使用Spring注释读取文件属性的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！