spring3中使用@value注解获取属性值

  在spring 3.0中，可以通过使用@value，对一些如xxx.properties文件中的文件，进行键值对的注入。

@Value有两种使用方式：@Value("#{configProperties['t1.msgname']}")或者@Value("${t1.msgname}")；

其次，下面我们来看看如何使用这两形式，在配置上有什么区别：
1、@Value("#{configProperties['t1.msgname']}")这种形式的配置中有“configProperties”，其实它指定的是配置文件的加载对象：配置如下：

<bean id="configProperties" class="org.springframework.beans.factory.config.PropertiesFactoryBean">
        <property name="locations">
            <list>
                <value>classpath:/config/t1.properties</value>
            </list>
        </property>
    </bean>

这样配置就可完成对属性的具体注入了；

2、@Value("${t1.msgname}")这种形式不需要指定具体加载对象，这时候需要一个关键的对象来完成PreferencesPlaceholderConfigurer，这个对象的配置可以利用上面配置1中的配置，也可以自己直接自定配置文件路径。
    如果使用配置1中的配置，可以写成如下情况：

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer">
        <property name="properties" ref="configProperties"/>
    </bean>

    如果直接指定配置文件的话，可以写成如下情况：

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer">
        <property name="location">
        <value>config/t1.properties</value>
        </property>
    </bean>

如果使用注解，可以写成如下情况：

@Configuration
@ComponentScan(basePackages = "com.dxz.config")
public class ServiceConfiguration2 { 


    public ServiceConfiguration2() {
        System.out.println("ServiceConfiguration zheli");
    }
    
    @Bean 
    public static PropertyPlaceholderConfigurer configurer() { 
         PropertyPlaceholderConfigurer ppc = new PropertyPlaceholderConfigurer();
         Resource resources = new ClassPathResource( "spring/config.properties" );
         ppc.setLocation(resources);
         return ppc; 
    } 
    
    @Bean
    public Configs2 configs2(@Value("${ds.user}") String user, @Value("${key1}") String key1) {
        Configs2 configs = new Configs2();
        configs.setApiKeyId(user);
        configs.setSecretApiKey(key1);
        System.out.println("in ServiceConfiguration" + configs);
        return configs;
    }
}

示例1：xml中配置PropertyPlaceholderConfigurer

1.首先在applicationContext.xml中加入： 

<beans xmlns="http://www.springframework.org/schema/beans"  
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
        xsi:schemaLocation="http://www.springframework.org/schema/beans   
         http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

 的命名空间，然后

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">    
    <property name="locations">    
        <list>    
            <value>classpath:test.properties</value>    
        </list>                
    </property>                                
</bean>  

3.创建test.properties 
   abc=123 
4.读取配置文件内容

import org.springframework.beans.factory.annotation.Value;     
import org.springframework.stereotype.Controller;     
import org.springframework.web.bind.annotation.RequestMapping;     
    
@RequestMapping("/admin/images")     
@Controller     
public class ImageAdminController {     
    
    private String imageDir;     
      
    @Value("${abc}")   
    public void setImageDir(String val) {     
        this.imageDir = val;     
    }  
}

 这样就将test.abc的值注入了imageDir中了。

 

示例2：context:property-placeholder

有时候需要从properties文件中加载配置，以前的方式是这样的：

<bean id="jdbcProperties" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">  
    <property name="locations">  
        <list>  
            <value>classpath*:/spring/jdbc.properties</value>  
        </list>  
    </property>  
</bean>  

最近发现这样也可以，代码更整洁：

<context:property-placeholder location="classpath:spring/jdbc.properties" />

在bean定义中依然可以通过“${}”这种方式来去值：

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">  
        <property name="driverClassName" value="${jdbc.driverClassName}" />  
        <property name="url" value="${jdbc.url}" />  
        <property name="username" value="${jdbc.username}" />  
        <property name="password" value="${jdbc.password}" />  
        <property name="initialSize" value="${jdbc.initialSize}" />  
        <property name="maxActive" value="${jdbc.maxActive}" />  
        <property name="maxIdle" value="${jdbc.maxIdle}" />  
        <property name="minIdle" value="${jdbc.minIdle}" />  
    </bean> 

说明：

<context:property-placeholder ... /> is the XML equivalent to the PropertyPlaceholderConfigurer. So, prefer that. The <util:properties/> simply factories a java.util.Properties instance that you can inject.

示例3：@PropertySource + Environment 

在spring3.1中（不是spring3.0）还可以这样：

package com.dxz.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;

@Configuration
@ComponentScan(basePackages = "com.dxz.config")
@PropertySource(value = "classpath:spring/config.properties")
public class ServiceConfiguration { 

    @Autowired 
    Environment environment; 

    public ServiceConfiguration() {
        System.out.println("ServiceConfiguration zheli");
    }
    
    //@Bean
    public javax.sql.DataSource dataSource(){ 
        String user = this.environment.getProperty("ds.user");
        System.out.println(user);
        return null;
    } 
}

配置文件config.properties：

key1=abc
key2=aaaaaaaaaaaaaaaaaaaa
key3=bbbbbbbbbbbbbbbbbbbbbbbbbbb
key4=cccccccccc
ds.user=admin

测试类：

package com.dxz.config;

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


public class Test {
    public static void main(String[] args) {

        ApplicationContext context = new AnnotationConfigApplicationContext(ServiceConfiguration.class);
        
        ServiceConfiguration hc2 = (ServiceConfiguration) context.getBean("serviceConfiguration");
        hc2.dataSource();
        
    }
}

结果：

十一月 02, 2017 10:20:43 上午 org.springframework.context.annotation.AnnotationConfigApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@3f91beef: startup date [Thu Nov 02 10:20:43 CST 2017]; root of context hierarchy
ServiceConfiguration zheli
admin

说明：

In Spring 3.0, you can "access" properties defined using the PropertyPlaceHolderConfigurer mechanism using the SpEl annotations:

PropertyPlaceHolderConfigurer可以在xml中配置，如上面提过的。

@Value("${ds.user}") 
private String user;

If you want to remove the XML all together, simply register the PropertyPlaceholderConfigurer manually using Java configuration. I prefer the 3.1 approach. But, if youre using the Spring 3.0 approach (since 3.1's not GA yet...), you can now define the above XML like this:

如果不采用xml配置，在java编码配置中可以用如下的注册方式来注册PropertyPlaceholderConfigurer，如下

示例4： PropertyPlaceholderConfigurer + @Value

package com.dxz.config;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;

@Configuration
@ComponentScan(basePackages = "com.dxz.config")
public class ServiceConfiguration2 { 


    public ServiceConfiguration2() {
        System.out.println("ServiceConfiguration zheli");
    }
    
    @Bean 
    public static PropertyPlaceholderConfigurer configurer() { 
         PropertyPlaceholderConfigurer ppc = new PropertyPlaceholderConfigurer();
         Resource resources = new ClassPathResource( "spring/config.properties" );
         ppc.setLocation(resources);
         return ppc; 
    } 
    
    @Bean
    public Configs2 configs2(@Value("${ds.user}") String user, @Value("${key1}") String key1) {
        Configs2 configs = new Configs2();
        configs.setApiKeyId(user);
        configs.setSecretApiKey(key1);
        System.out.println("in ServiceConfiguration" + configs);
        return configs;
    }
    
}

package com.dxz.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class TestConfigs2 {

    @Autowired
    Configs2 configs2;
    
    @Autowired
    Configs configs;
    
    public void testConfigs2() {
        System.out.println("configs:"+configs.getApiKeyId());
        System.out.println("configs2:"+configs2.getApiKeyId());
    }
}

package com.dxz.config;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class Configs {

    @Value("${key1}")
    public String apiKeyId;

    @Value("${ds.user}")
    public String secretApiKey;

    public String getApiKeyId() {
        return apiKeyId;
    }

    public String getSecretApiKey() {
        return secretApiKey;
    }
}

package com.dxz.config;

//@Component
public class Configs2 {

    public String apiKeyId;

    public String secretApiKey;

    public String getApiKeyId() {
        return apiKeyId;
    }

    public void setApiKeyId(String apiKeyId) {
        this.apiKeyId = apiKeyId;
    }

    public String getSecretApiKey() {
        return secretApiKey;
    }

    public void setSecretApiKey(String secretApiKey) {
        this.secretApiKey = secretApiKey;
    }

    @Override
    public String toString() {
        return "Configs2 [apiKeyId=" + apiKeyId + ", secretApiKey=" + secretApiKey + "]";
    }

}

测试类：

package com.dxz.config;

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


public class Test {
    
    public static void main(String[] args) {

        ApplicationContext context = new AnnotationConfigApplicationContext(ServiceConfiguration2.class);
        
        TestConfigs2 hc2 = (TestConfigs2) context.getBean("testConfigs2");
        hc2.testConfigs2();
        
        
    }
}

结果：

ServiceConfiguration zheli
ServiceConfiguration zheli
in ServiceConfigurationConfigs2 [apiKeyId=admin, secretApiKey=abc]
configs:abc
configs2:admin

说明：

1、static类型的会优先在spring容器中注册。Note that the PPC is defined using a static bean definition method. This is required to make sure the bean is registered early, because the PPC is a BeanFactoryPostProcessor - it can influence the registration of the beans themselves in the context, so it necessarily has to be registered before everything else.

2、上面示例中有2中场景：

configs是spring容器管理的bean，configs的成员变量通过@Value注解获取配置文件的配置值；

configs2是普通的pojo类，没有注册到spring容器中，在初始化时，通过其创建方法中通过@Value注解获取传入配置文件中的配置值；

不要忘记这时候需要一个关键的对象来完成PreferencesPlaceholderConfigurer来支持；