Java的：读取属性使用Spring注解文件 [英] Java: read properties file using spring annotations
问题描述
我在春天初学者。我想学习如何阅读使用弹簧属性文件。互联网搜索后，我发现我可以使用@value和@PropertySource注解来实现这一目标。我创建了具有以下结构和类codeS项目：
I'm beginner in spring. 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());
}
}
属性文件我是从所谓的config.properties阅读，它包含以下行：
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，我得到了一个包含以下异常堆栈跟踪：
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
它是春天的呼唤豆有问题吗？或者，也许是属性文件路径的问题？还是其他的事情吗？
Is it a problem of spring calling beans? Or maybe is it a problem of properties file path? Or an other thing?
推荐答案
我可以看到几个问题，在code。
I can see several issues in the code.
1）您的占位值应该在表格 $ {mogodb.url} ，而不是＃{mongodb.url} 。该＃有不同的含义（见春天防爆pressions 的）。
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 豆做值的注入
2) You are going to need a PropertySourcesPlaceholderConfigurer bean to do the injection of the values
3）你迟早将不得不浮动一些豆类周围，并在我会用 @ComponentScan 来允许上下文知道这些，您无需提逐一
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）如果你使用 ComponentScan 来得到豆子，你将不得不一旦提供 AppConfigMongoDB 豆
4) If you use ComponentScan to get the beans, you are going to have to provide AppConfigMongoDB bean once
我结束了这些课程后做一切：
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;
}
}
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