Spring（十）：Spring配置Bean（三）Bean的作用域、使用外部属性文件

Bean的作用域：

支持四种配置，分别是singleton，prototype，request，session。

singleton

默认情况下在spring confinguration xml文件中的一个bean配置中，如果不指定scope属性，则这个scope默认值为singleton。

如何把一个bean配置为scope='singleton'：

Person.java

package com.dx.beans.scope;

public class Person {
    private int id;
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Person() {
        System.out.println("Person's Constructor...");
    }

    @Override
    public String toString() {
        return "Person [id=" + id + ", name=" + name + "]";
    }
}

springcfg.xml

    <bean id="person" class="com.dx.beans.scope.Person" scope="singleton">
        <property name="id" value="1"></property>
        <property name="name" value="person demo"></property>
    </bean>

配置为singleton的bean将会在初始化Spring时，初始化该bean的类。

package com.dx.beans.scope;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Client {
    public static void main(String[] args) {
        ApplicationContext cxt = new ClassPathXmlApplicationContext("springcfg.xml");
    }
}

打印信息为：

Person's Constructor...

而且在以后调用该bean时，不会再初始化给bean的类。

package com.dx.beans.scope;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Client {
    public static void main(String[] args) {
        ApplicationContext cxt = new ClassPathXmlApplicationContext("springcfg.xml");
        
        Person person = (Person) cxt.getBean("person");
        Person person1 = (Person) cxt.getBean("person");

        System.out.println(person);
        System.out.println(person1);
    }
}

打印信息为：

Person's Constructor...
Person [id=1, name=person demo]
Person [id=1, name=person demo]

prototype

 每次调用时，都会实例化一次bean的class。

spring configuration xml配置文件为：

<?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:p="http://www.springframework.org/schema/p"
    xmlns:util="http://www.springframework.org/schema/util"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.3.xsd">

    <bean id="person" class="com.dx.beans.scope.Person" scope="prototype">
        <property name="id" value="1"></property>
        <property name="name" value="person demo"></property>
    </bean>
</beans>

此时，客户端调用：

package com.dx.beans.scope;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Client {
    public static void main(String[] args) {
        ApplicationContext cxt = new ClassPathXmlApplicationContext("springcfg.xml");
        
        Person person = (Person) cxt.getBean("person");
        System.out.println(person);
        
        Person person1 = (Person) cxt.getBean("person");
        System.out.println(person1);
    }
}

打印信息为：

Person's Constructor...
Person [id=1, name=person demo]
Person's Constructor...
Person [id=1, name=person demo]

web环境作用域 request,session

request,session应用在web环境作用域。

使用外部属性文件

1） 在配置文件里配置Bean时，有时需要在Bean的配置里混入系统部署的细节信息（例如：文件路径、数据源配置信息等），而这些部署细节实际上需要和Bean配置相分离。

2）Spring提供了一个PropertyPlaceholderConfigurer的BeanFactory后置处理器。这个处理器允许用户将Bean配置的部分内容外移到属性文件中，可以在Bean配置文件里使用形式为${var}的变量，PropertyPlaceholderConfigurer从属性文件里加载属性，并使用这些属性值来替换变量。

3）Spring还允许在属性文件中使用${propertyName}，以实现属性之间的相互引用。

注册PropertyPlaceholderConfigurer

spring2.0时：

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
     <property name="location" value="classpath:jdbc.properties"></property >
</bean>

spring2.5之后：

可通过<context:property-placeholder>元素简化

--添加命名空间：<beans>中添加context Schema定义（xmlns:context="http://www.springframework.org/schema/context"）
--在配置文件下加入配置：<context:property-placeholder location="classpath:db.properties"/>

需求：使用c3p0组件连接数据库，并把它注册到spring中。

使用外部文件之前：

 pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.dx</groupId>
    <artifactId>springlearning</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <repositories>
        <repository>
            <id>sonatype-nexus-snapshots</id>
            <name>Sonatype Nexus Snapshots</name>
            <url>http://maven.aliyun.com/nexus/content/groups/public</url>
            <releases>
                <enabled>false</enabled>
            </releases>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </repository>
    </repositories>
    <properties>
        <org.springframework.version>4.3.8.RELEASE</org.springframework.version>
    </properties>
    <dependencies>
        <!-- https://mvnrepository.com/artifact/commons-logging/commons-logging -->
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <!-- Expression Language (depends on spring-core) Define this if you use 
            Spring Expression APIs (org.springframework.expression.*) -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-expression</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <!-- Bean Factory and JavaBeans utilities (depends on spring-core) Define 
            this if you use Spring Bean APIs (org.springframework.beans.*) -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <!-- Application Context (depends on spring-core, spring-expression, spring-aop, 
            spring-beans) This is the central artifact for Spring's Dependency Injection 
            Container and is generally always defined -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <!-- JDBC Data Access Library (depends on spring-core, spring-beans, spring-context, 
            spring-tx) Define this if you use Spring's JdbcTemplate API (org.springframework.jdbc.*) -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>${org.springframework.version}</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.36</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/c3p0/c3p0 -->
        <dependency>
            <groupId>c3p0</groupId>
            <artifactId>c3p0</artifactId>
            <version>0.9.1.2</version>
        </dependency>

    </dependencies>
    <build>
        <finalName>demo</finalName>
    </build>
</project>

bean-properties.xml

<?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: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/context http://www.springframework.org/schema/context/spring-context-4.3.xsd">
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="root"></property>
        <property name="password" value="root"></property>
        <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/dlog32"></property>
        <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
    </bean>
</beans>

Client.java调用：

package com.dx.beans.properties;

import javax.sql.DataSource;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Client {
    public static void main(String[] args) throws Exception {
        ApplicationContext cxt = new ClassPathXmlApplicationContext("beans-properties.xml");
        DataSource dataSource = (DataSource) cxt.getBean("dataSource");
        
        System.out.println(dataSource.getConnection());
    }
}

使用外部文件之后：

添加外部文件c3p0-db.properties

db.user=root
db.password=root
db.jdbcUrl=jdbc:mysql://localhost/dlog32
db.driverClass=com.mysql.jdbc.Driver

修改spring bean配置文件beans-properties.xml

<?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: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/context http://www.springframework.org/schema/context/spring-context-4.3.xsd">
    <!-- 导入外部文件 -->
    <context:property-placeholder location="classpath:c3p0-db.properties" />
    
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <!-- 使用外部文件的配置信息替代配置项中的值 -->
        <property name="user" value="${db.user}"></property>
        <property name="password" value="${db.password}"></property>
        <property name="jdbcUrl" value="${db.jdbcUrl}"></property>
        <property name="driverClass" value="${db.driverClass}"></property>
    </bean>
</beans>