spring学习（二十）--spring注解之@Value

通过@Value将外部的值动态注入到Bean中，使用的情况有：

• 注入普通字符串
• 注入操作系统属性
• 注入表达式结果
• 注入其他Bean属性：注入beanInject对象的属性another
• 注入文件资源

• 注入URL资源

  详细代码见：

　　 @Value("normal")
    private String normal; // 注入普通字符串

    @Value("#{systemProperties['os.name']}")
    private String systemPropertiesName; // 注入操作系统属性

    @Value("#{ T(java.lang.Math).random() * 100.0 }")
    private double randomNumber; //注入表达式结果

    @Value("#{beanInject.another}")
    private String fromAnotherBean; // 注入其他Bean属性：注入beanInject对象的属性another，类具体定义见下面

    @Value("classpath:com/hry/spring/configinject/config.txt")
    private Resource resourceFile; // 注入文件资源

    @Value("http://www.baidu.com")
    private Resource testUrl; // 注入URL资源

示例：获取application.properties中的name字段值，以及通过Resource获取properties文件的内容

spring-annotion.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd 
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd ">

        <!-- 支持@Value获取properties中的值 -->
        <bean id="appProperty" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
            <property name="locations">
                <array>
                    <value>classpath:application.properties</value>
                </array>
            </property>
        </bean>
    
    <!-- 配置自动扫描的包 -->
    <context:component-scan base-package="springAnnotions"></context:component-scan>

</beans>

applicatio.properties

name=littleball

ValueAnnotion.java

package springAnnotions;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Properties;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.io.Resource;
import org.springframework.stereotype.Component;

@Componentpublic class ValueAnnotion {
    
    //冒号后边的：qiaozhong为默认值，当从properties中没有取到name的时候，就取默认值给name
    @Value("${name:qiaozhong}")
    private String name;
    
    @Value("classpath:application.properties")
    private Resource resource;
    
    public static void main(String[] args) throws IOException {
        ApplicationContext aContext = new ClassPathXmlApplicationContext("classpath:springConfig/spring-annotions.xml");
        ValueAnnotion valueAnnotion = aContext.getBean(ValueAnnotion.class);
        System.out.println(valueAnnotion.getName());
        File file = valueAnnotion.getResource().getFile();
        if (valueAnnotion.getResource().isReadable()) {
            System.out.println(getFileContent(valueAnnotion.getResource().getInputStream()));
            System.out.println(getFileContent(file, "name"));
        }
    }
    
    public String getName(){
        return name;
    }
    
    public Resource getResource(){
        return resource;
    }
    
    /**
     * 获取file文件的内容
     * @param is
     * @throws IOException
     */
    public static String getFileContent(InputStream is) throws IOException {
        String result = "";
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            String line;
            while ((line=br.readLine()) != null) {
                result += line;
            }
            if (is != null) {
                is.close();
            }
            if (br != null) {
                br.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }
    
    /**
     * 获取file文件中key对应的value
     * @param file
     * @return
     */
    public static String getFileContent(File file, String key){
        try {
            if (file.exists()) {
                Properties propertie = new Properties();
                propertie.load(new FileInputStream(file));
                return propertie.getProperty(key);
            }
            return null;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }
}

执行结果：

littleball
name=littleball
littleball