学步园

并不是每一个JavaBean都只有一个无参数的构造方法，如果一个JavaBean的构造方法的参数有一个或多个，就需要使用<constructor-reg>标签来为这些构造方法设置相应的参数值。

ConstructorBean.java

package chapter22;

public class ConstructorBean {
    private String name;
    private String message;
    private int number;
    
    public ConstructorBean(String name) {
        super();
        this.name = name;
        System.out.println("ConstructorBean(String name) 构造函数被调用");
    }
    public ConstructorBean(String name, int number) {
        super();
        this.name = name;
        this.number = number;
        System.out.println("ConstructorBean(String name,int number) 构造函数被调用");
    }
    public ConstructorBean(String name, String message) {
        super();
        this.name = name;
        this.message = message;
        System.out.println("ConstructorBean(String name,String message) 构造函数被调用");
    }
    
    public String getName() {
        return name;
    }
    public String getMessage() {
        return message;
    }
    public int getNumber() {
        return number;
    }
}

TestConstructorBean.java

package chapter22;

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

public class TestConstructorBean {
    public static void main(String args[])
    {
        ApplicationContext ctx=new FileSystemXmlApplicationContext("src//ConstructorBean.xml");
        //ApplicationContext ctx=new FileSystemXmlApplicationContext("src//a.xml");
        ConstructorBean cb=(ConstructorBean)ctx.getBean("constructor1");
        System.out.println(cb.getName());
        System.out.println("--------------------------------");
        
        cb=(ConstructorBean)ctx.getBean("constructor2");
        System.out.println("name:"+cb.getName());
        System.out.println("message:"+cb.getMessage());
        System.out.println("number:"+cb.getNumber());
        System.out.println("--------------------------------");
        //指定
        cb=(ConstructorBean)ctx.getBean("constructor3");
        System.out.println("name:"+cb.getName());
        System.out.println("message:"+cb.getMessage());
        System.out.println("number:"+cb.getNumber());
        System.out.println("--------------------------------");
        //指定第二个参数类型为int型。这样会匹配第2个构造函数。
        cb=(ConstructorBean)ctx.getBean("constructor4");
        System.out.println("name:"+cb.getName());
        System.out.println("message:"+cb.getMessage());
        System.out.println("number:"+cb.getNumber());
        System.out.println("--------------------------------");
        //通过使用<consturctor-arg>标签的index属性来改变传递参数的顺序
        cb=(ConstructorBean)ctx.getBean("constructor5");
        System.out.println("name:"+cb.getName());
        System.out.println("message:"+cb.getMessage());
        System.out.println("number:"+cb.getNumber());
    }    
}

constructor.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:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"><!--要使用第1个构造方法创建ConstructorBean对象非常简单，Spring会自动寻找ConstructorBean类中只有一个参数的构造方法。-->
    <bean id="constructor1" class="chapter22.ConstructorBean">
        <constructor-arg>
            <value>Michael</value></constructor-arg></bean>

<!--这里第二个参数是20，一般认为Spring会自动匹配第二种方法。但是实现上确实调用了第3中方法。因为在Spring中搜索Bean的构造方法时，会先将参数值当成String类型数据来看。-->
    <bean id="constructor2" class="chapter22.ConstructorBean">
        <constructor-arg>
            <value>bill</value></constructor-arg>
        <constructor-arg>
            <value>20</value></constructor-arg></bean>

<!--这里的第二个参数使用了类型限定，即指定第二个参数所对应的类型是int，因此Spring会匹配第2中方法。-->
    <bean id="constructor3" class="chapter22.ConstructorBean">
        <constructor-arg>
            <value>bill</value></constructor-arg>
        <constructor-arg type="int">
            <value>20</value>
        </constructor-arg></bean>

<!--默认情况下Spring匹配构造函数是按参数的顺序匹配的。-->

    <bean id="constructor4" class="chapter22.ConstructorBean">
        <constructor-arg>
            <value>bike</value></constructor-arg>
        <constructor-arg>
            <value>John</value>
        </constructor-arg></bean>

<!--但是可以通过index属性来表示构造方法参数的位置，从0开始。-->

    <bean id="constructor5" class="chapter22.ConstructorBean">
        <constructor-arg index="1">
            <value>bike</value>
        </constructor-arg>
        <constructor-arg index="0">
            <value>John</value>
        </constructor-arg></bean>
</beans>

Spring装配多个配置文件的方法

TestTwoConfigueFile.java

package chapter22;

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

public class TestTwoConfigueFile {
    public static void main(String args[])
    {
        //使用FileSystemXmlApplicationContext
        //ApplicationContext ctx=new FileSystemXmlApplicationContext(new String[]{"src//applicationContext.xml","src//ConstructorBean.xml"});
        //使用ClassPathXmlApplicationContext
        ApplicationContext ctx=new ClassPathXmlApplicationContext(new String[]{"applicationContext.xml","ConstructorBean.xml"});
        System.out.println("--------------------------------");

        MyBean mb=(MyBean)ctx.getBean("myBean");
        //System.out.println(mb.getHello());
        System.out.println(mb.getHello().getGreeting());
        System.out.println(mb.getStrName());
        System.out.println("--------------------------------");

        ConstructorBean cb=(ConstructorBean)ctx.getBean("constructor1");
        System.out.println(cb.getName());
    }
}