Spring依赖注入：自动注入properties文件中的配置

曾经终败给现在 2021-09-16 01:54 491阅读 0赞

**Spring依赖注入：自动注入properties文件中的配置**：很多情况下我们需要在配置文件中配置一些属性，然后注入到bean中，Spring提供了org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer类，可以方便我们使用注解直接注入properties文件中的配置。

下面我们看下具体如何操作：

首先要新建maven项目，并在pom文件中添加spring依赖，如下pom.xml文件：

`<project xmlns=``"https://maven.apache.org/POM/4.0.0"` `xmlns:xsi=``"https://www.w3.org/2001/XMLSchema-instance"` `xsi:schemalocation=``"https://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"``>  <modelversion>``4.0``.``0``</modelversion>`

`  ``<groupid>cn.outofmemory</groupid>`

`  ``hellospring.properties.annotation</artifactid>`

`  ``<version>``0.0``.``1``-SNAPSHOT</version>`

`  ``<packaging>jar</packaging>`

`  ``<name>hellospring.properties.annotation</name>`

`  ``<url>https:``//maven.apache.org</url>`

`  ``<properties>`

`    ``<project.build.sourceencoding>UTF-``8``</project.build.sourceencoding>`

`    ``<org.springframework-version>``3.0``.``0``.RC2</org.springframework-version>`

`  ``</properties>`

`  ``<dependencies>`

`    ``<dependency>`

`      ``<groupid>junit</groupid>`

`      ``junit</artifactid>`

`      ``<version>``3.8``.``1``</version>`

`      ``<scope>test</scope>`

`    ``</dependency>             `

`    ```

`    ``<dependency>`

`        ``<groupid>org.springframework</groupid>`

`        ``spring-context</artifactid>`

`        ``<version>${org.springframework-version}</version>`

`    ``</dependency>`

`  ``</dependencies>`

`</project>`

要自动注入properties文件中的配置，需要在spring配置文件中添加org.springframework.beans.factory.config.PropertiesFactoryBean和org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer的实例配置：

如下spring配置文件appContext.xml

``

`<beans xmlns=``"https://www.springframework.org/schema/beans"` `xmlns:context=``"https://www.springframework.org/schema/context"` `xmlns:xsi=``"https://www.w3.org/2001/XMLSchema-instance"` `xsi:schemalocation="https://www.springframework.org/schema/beans`

` ``https:``//www.springframework.org/schema/beans/spring-beans-3.0.xsd`

` ``https:``//www.springframework.org/schema/context`

` ``https:``//www.springframework.org/schema/context/spring-context-3.0.xsd ">`

`    ```

`    ``<context:annotation-config>`

`    ``<context:component-scan base-``package``=``"cn.outofmemory.hellospring.properties.annotation"``>`

`    ``</context:component-scan>`

`    ``<bean``class``=``"org.springframework.beans.factory.config.PropertiesFactoryBean"` `id=``"configProperties"``>`

`        ``<property name=``"locations"``>`

`            ``<list>`

`                ``<value>classpath*:application.properties</value>`

`            ``</list>`

`        ``</property>`

`    ``</bean>`

`    ``<bean``class``=``"org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer"` `id=``"propertyConfigurer"``>`

`        ``<property name=``"properties"` `ref=``"configProperties"``>`

`    ``</property></bean>   `

`</context:annotation-config></beans>`

在这个配置文件中我们配置了注解扫描，和configProperties实例和propertyConfigurer实例。这样我们就可以在java类中自动注入配置了，我们看下java类中如何做：

<table> 
 <tbody> 
 <tr> 
 <td> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 </td> 
 <td> <code>package</code> <code>cn.outofmemory.hellospring.properties.annotation;</code> &nbsp; <code>import</code> <code>org.springframework.beans.factory.annotation.Value;</code> <code>import</code> <code>org.springframework.stereotype.Component;</code> &nbsp; <code>@Component</code> <code>public</code> <code>class</code> <code>MySQLConnectionInfo { </code> &nbsp; <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>@Value</code><code>(</code><code>"#{configProperties['mysql.url']}"</code><code>)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>private</code> <code>String url;</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>@Value</code><code>(</code><code>"#{configProperties['mysql.userName']}"</code><code>)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>private</code> <code>String userName;</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>@Value</code><code>(</code><code>"#{configProperties['mysql.password']}"</code><code>)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>private</code> <code>String password;</code> &nbsp; <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>/**</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>* @return the url</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>*/</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>public</code> <code>String getUrl() { </code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>return</code> <code>url;</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>}</code> &nbsp; <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>/**</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>* @return the userName</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>*/</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>public</code> <code>String getUserName() { </code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>return</code> <code>userName;</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>}</code> &nbsp; <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>/**</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>* @return the password</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>*/</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>public</code> <code>String getPassword() { </code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>return</code> <code>password;</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>}</code> <code>}</code> </td> 
 </tr> 
 </tbody> 
</table>

自动注入需要使用@Value注解，这个注解的格式\#\{configProperties\['mysql.url'\]\}其中configProperties是我们在appContext.xml中配置的beanId，mysql.url是在properties文件中的配置项。

properties文件的内容如下：

<table> 
 <tbody> 
 <tr> 
 <td> 1 2 3 </td> 
 <td> <code>mysql.url=mysql's url</code> <code>mysql.userName=mysqlUser</code> <code>mysql.password=mysqlPassword</code> </td> 
 </tr> 
 </tbody> 
</table>

最后我们需要测试一下以上写法是否有问题，如下App.java文件内容：

<table> 
 <tbody> 
 <tr> 
 <td> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 </td> 
 <td> <code>package</code> <code>cn.outofmemory.hellospring.properties.annotation;</code> &nbsp; <code>import</code> <code>org.springframework.context.ApplicationContext;</code> <code>import</code> <code>org.springframework.context.annotation.AnnotationConfigApplicationContext;</code> <code>import</code> <code>org.springframework.context.support.ClassPathXmlApplicationContext;</code> &nbsp; <code>/**</code> <code>&nbsp;</code><code>* Hello world!</code> <code>&nbsp;</code><code>*</code> <code>&nbsp;</code><code>*/</code> <code>public</code> <code>class</code> <code>App </code> <code>{ </code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>public</code> <code>static</code> <code>void</code> <code>main( String[] args )</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>{ </code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>ApplicationContext appContext = </code><code>new</code> <code>ClassPathXmlApplicationContext(</code><code>"appContext.xml"</code><code>);</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>MySQLConnectionInfo connInfo = appContext.getBean(MySQLConnectionInfo.</code><code>class</code><code>);</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>System.out.println(connInfo.getUrl());</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>System.out.println(connInfo.getUserName());</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>System.out.println(connInfo.getPassword());</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>}</code> <code>}</code> </td> 
 </tr> 
 </tbody> 
</table>

在main方法中首先声明了appContext，然后获得了自动注入的MySQLConnectionInfo的实例，然后打印出来，运行程序会输出配置文件中配置的值。