十、spring框架中對property屬性文件的讀取的5種方式

1、方式一：通過spring框架 PropertyPlaceholderConfigurer 工具實現

    <bean id="propertyConfig" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="ignoreUnresolvablePlaceholders" value="true"/>
        <property name="locations">
            <value>classpath:conf/jdbc.properties</value>
        </property>
        <property name="fileEncoding">
            <value>UTF-8</value>
        </property>
        <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" />
    </bean>
    
    <!-- 數據源配置 -->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
          destroy-method="close">
        <property name="driverClassName" value="${database.connection.driver}"/>
        <property name="url" value="${database.connection.url}"/>
        <property name="username" value="${database.connection.username}"/>
        <property name="password" value="${database.connection.password}"/>
    </bean>
    <!-- DAL客戶端接口實現->
    <bean id="dalClient" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"/>
    </bean>

2、方式二：簡化配置

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:jee="http://www.springframework.org/schema/jee" xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee.xsd
    http://www.springframework.org/schema/context  http://www.springframework.org/schema/context/spring-context.xsd
    http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd
    ">
    <context:property-placeholder location="classpath:conf/jdbc.properties" ignore-unresolvable="true"/>
    <!-- 數據源配置 -->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
          destroy-method="close">
        <property name="driverClassName" value="${database.connection.driver}"/>
        <property name="url" value="${database.connection.url}"/>
        <property name="username" value="${database.connection.username}"/>
        <property name="password" value="${database.connection.password}"/>
    </bean>
    <!-- DAL客戶端接口實現-->
    <bean id="dalClient" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"/>
    </bean>
    <!--備注：如果${} 這種寫法無法讀取到，或者編譯出錯，則增加ignore-unresolvable="true"的屬性信息，並添加上文的 命名空間信息-->
    
    jdbc.properties文件：
    database.connection.driver=com.mysql.jdbc.Driver
    database.connection.url=jdbc:mysql://*.*.*.*:3306/mysql?characterEncoding=utf-8
    database.connection.username=*
    database.connection.password=*

    上述配置理解：
    1）ignore-unresolvable屬性的示意：
    <xsd:documentation><![CDATA[
    Specifies if failure to find the property value to replace a key should be ignored.
    Default is "false", meaning that this placeholder configurer will raise an exception
    if it cannot resolve a key. Set to "true" to allow the configurer to pass on the key
    to any others in the context that have not yet visited the key in question.
    ]]>
    翻譯后：指定是否應忽略未能找到用於替換鍵的屬性值。默認值為“false”，表示如果它無法解析密鑰，此占位符配置程序將引發異常。設置為“true”以允許配置程序傳遞密鑰對於上下文中尚未訪問相關密鑰的任何其他用戶。
    2) 為簡化 PropertyPlaceholderConfigurer 的使用，Spring提供了<context:property-placeholder location="classpath:jdbc.properties" />元素,啟用它后，開發者便不用配置PropertyPlaceholderConfigurer對象了。PropertyPlaceholderConfigurer內置的功能非常豐富，如果它未找到${xxx}中定義的xxx鍵，它還會去JVM系統屬性(System.getProperty())和環境變量(System.getenv())中尋找。其通過啟用systemPropertiesMode和searchSystemEnvironment屬性，開發者能夠控制這一行為。context:property-placeholder大大的方便了我們數據庫的配置。這樣就可以為spring配置的bean的屬性設置值了。
    備注：spring容器中最多只能定義一個 context:property-placeholder，否則會報錯：Could not resolve placeholder XXX,但如果想引入多個屬性文件怎么辦那，可以使用通配符：<context:property-placeholder location="classpath*:conf*.properties"/>

3、方式三：通過對spring PropertyPlaceholderConfigurer bean工廠后置處理器的實現，在java程序中進行屬性文件的讀取

    <bean id="propertyConfigurer" class="com.weblearn.utils.PropertyConfigurer">
        <property name="locations">
            <list>
                <value>classpath:conf/web-sys-relation.properties</value>
                <value>classpath:conf/jdbc.properties</value>
                <value>classpath:conf/main-setting-web.properties</value>
            </list>
        </property>
        <property name="fileEncoding" value="UTF-8"/>
    </bean>
    <!-- DAL客戶端接口實現-->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
          destroy-method="close">
        <property name="driverClassName" value="${database.connection.driver}"/>
        <property name="url" value="${database.connection.url}"/>
        <property name="username" value="${database.connection.username}"/>
        <property name="password" value="${database.connection.password}"/>
    </bean>
    
    <bean id="dalClient" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"/>
    </bean>

public class PropertyConfigurer extends PropertyPlaceholderConfigurer {
        /* 
            PropertyPlaceholderConfigurer 是個bean工廠后置處理器的實現，也就是 BeanFactoryPostProcessor 接口的一個實現。
            在Spring中，使用PropertyPlaceholderConfigurer可以在XML配置文件中加入外部屬性文件，當然也可以指定外部文件的編碼。PropertyPlaceholderConfigurer可以將上下文
       （配置文 件）中的屬性值放在另一個單獨的標准java Properties文件中去。在XML文件中用${key}替換指定的properties文件中的值。這樣的話，只需要對properties文件進
       行修改，而不用對xml配置文件進行修改。
            引入外部文件后，就可以在xml中用${key}替換指定的properties文件中的值，通常項目中都會將jdbc的配置放在properties文件中。
            在啟動容器時，初始化bean時，${key}就會替換成properties文件中的值。
        */

        //存取properties配置文件key-value結果
        private Properties props;

        @Override
        protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)
                throws BeansException {
            super.processProperties(beanFactoryToProcess, props);
            this.props = props;
        }

        public String getProperty(String key) {
            return this.props.getProperty(key);
        }

        public String getProperty(String key, String defaultValue) {
            return this.props.getProperty(key, defaultValue);
        }

        public Object setProperty(String key, String value) {
            return this.props.setProperty(key, value);
        }

    }

    @Controller
    @RequestMapping("/")
    public class TestController {
        @Autowired
        PropertyConfigurer propertyConfigurer;

        @RequestMapping("/index.do")
        public String getIndex(HttpServletRequest request, HttpServletResponse response, Model model) {
            Map map = new HashMap<String, Object>();
            map.put("orderNo", "111");

            String address1 = propertyConfigurer.getProperty("static.picture.address1");
            String resRoot = propertyConfigurer.getProperty("resRoot");
            String envName = propertyConfigurer.getProperty("database.connection.username");
            String keyzjbceshi = propertyConfigurer.getProperty("keyceshi");


            map.put("address1", address1);
            map.put("resRoot", resRoot);
            map.put("envName", envName);
            map.put("keyzjbceshi", keyzjbceshi);

            model.addAllAttributes(map);
            return "index/index.ftl";
        }
    }

4、方式四：通過ClassPathResource類進行屬性文件的讀取使用

    public class ReadPropertiesUtils1 {
        private static final Logger LOGGER = LoggerFactory.getLogger(ReadPropertiesUtils1.class);

        private static Properties props = new Properties();

        static {
            ClassPathResource cpr = new ClassPathResource("conf/ref-system-relation.properties");// 會重新加載spring框架
            try {
                props.load(cpr.getInputStream());
            } catch (IOException exception) {
                LOGGER.error("ReadPropertiesUtils1 IOException", exception);
            }
        }

        private ReadPropertiesUtils1() {

        }

        public static String getValue(String key) {
            return (String) props.get(key);
        }

        public static void main(String[] args) {
            System.out.println("static.picture.address1>>>"+ ReadPropertiesUtils1.getValue("static.picture.address1"));
            System.out.println("static.picture.address2>>>"+ ReadPropertiesUtils1.getValue("static.picture.address2"));
        }

    }

5、方式五：通過ContextClassLoader進行屬性文件的讀取使用

public class ReadPropertiesUtils2 {
        private static final Logger LOGGER = LoggerFactory.getLogger(ReadPropertiesUtils2.class);

        public static String getValue(String key) {
            Properties properties = new Properties();
            try {
                InputStream inputStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("conf/ref-system-relation.properties");
                properties.load(inputStream);
            } catch (FileNotFoundException e) {
                LOGGER.error("conf/web-sys-relation.properties文件沒有找到異常", e);
            } catch (IOException e) {
                LOGGER.error("IOException", e);
            }
            return properties.getProperty(key);
        }

        public static void main(String[] args) {
            System.out.println("static.picture.address1>>>" + ReadPropertiesUtils2.getValue("static.picture.address1"));
            System.out.println("static.picture.address2>>>" + ReadPropertiesUtils2.getValue("static.picture.address2"));
        }
    }

參看博文：https://blog.csdn.net/wrs120/article/details/84554366