Spring根据XML配置文件注入属性 其实也是造bean，看看是使用constructor还是setter顺带完成属性赋值

方法一使用setter方法

package com.swift;

public class Book {
    private String bookName;

    public void setBook(String bookName) {
        this.bookName = bookName;
    }

    @Override
    public String toString() {
        return "Book [book=" + bookName + "]";
    }
}

在Spring框架中，假定Servlet类中不能直接生成Book类的对象，并注入String bookName的属性值

而需要通过配置文件xml的方法

<?xml version="1.0" encoding="UTF-8"?>
<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.xsd">
<!-- IoC 控制反转 SpringSpring根据XML配置文件注入属性 -->
<bean id="book" class="com.swift.Book">
<property name="bookName" value="三体——黑暗森林"></property>
</bean>
</beans>

Servlet类代码：

package com.swift;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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

@WebServlet("/book")
public class BookServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public BookServlet() {
        super();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().append("Served at: ").append(request.getContextPath());
        @SuppressWarnings("resource")
        //就是下边这几句了
        ApplicationContext context=new ClassPathXmlApplicationContext("a.xml");
        Book book=(Book) context.getBean("book");
        String bookInfo=book.fun();
        response.getWriter().println();
        response.getWriter().append(bookInfo);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

注意

beans 、context、core 和expression核心jar包

以及commons-logging 和log4j两个jar包不要缺少

方法二使用有参构造方法

package com.swift;

public class Book {
    private String bookName;

    public Book() {}
    public Book(String bookName) {
        this.bookName=bookName;
    }

    public String fun() {
        return "Book [book="+ bookName+"]";
    }
}

这时xml配置文件代码如下：

<?xml version="1.0" encoding="UTF-8"?>
<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.xsd">
<!-- IoC 控制反转 SpringSpring根据XML配置文件生成对象 -->
<bean id="book" class="com.swift.Book">
<constructor-arg name="bookName" value="基督山伯爵"></constructor-arg>
</bean>
</beans>

最后，Servlet类代码如下：

package com.swift;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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

@WebServlet("/book2")
public class BookServlet2 extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public BookServlet2() {
        super();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().append("Served at: ").append(request.getContextPath());
        @SuppressWarnings("resource")
        //就是下边这几句了
        ApplicationContext context=new ClassPathXmlApplicationContext("b.xml");
        Book book=(Book) context.getBean("book");
        String bookInfo=book.fun();
        response.getWriter().println();
        response.getWriter().append(bookInfo);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

有参构造多参数情况

package cn.itcast.entity;

public class User {

    private String name;
    private Integer age;
    private Car car;
    public User() {
        super();
        // TODO Auto-generated constructor stub
    }
    public User(String name, Integer age) {
        super();
        this.name = name;
        this.age = age;
    }

    public User(String name, Integer age, Car car) {
        System.out.println("public User(String name, Integer age, Car car)");
        this.name = name;
        this.age = age;
        this.car = car;
    }
    public User(Integer age,String name, Car car) {
        System.out.println("public User(Integer age,String name, Car car)");
        this.name = name;
        this.age = age;
        this.car = car;
    }
    @Override
    public String toString() {
        return "User [name=" + name + ", age=" + age + ", car=" + car + "]";
    }

}

此时constructor-arg只使用name和value两个是不够区分的,可以加入索引index设置次序 加入type判断参数类型 自定义对象的值用ref

XML配置文件配置方法:

<?xml version="1.0" encoding="UTF-8"?>
<!-- 导入schema
约束的位置在:
    ..\spring-framework-4.2.4.RELEASE\docs\spring-framework-reference\html\xsd-configuration.html
    文件中。
注意：要导入schema约束
-->
<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.xsd">

<!-- <bean name="user" class="cn.itcast.entity.User">
    <property name="name" value="spring"></property>
    <property name="age" value="18"></property>
    <property ref="car" name="car"></property>

</bean>  -->     

<bean name="user" class="cn.itcast.entity.User">
    <constructor-arg name="name" value="gaoyang" index="0" type="java.lang.String"></constructor-arg>
    <constructor-arg name="age" value="26" index="1" type="java.lang.Integer"></constructor-arg>
    <constructor-arg name="car" ref="car" index="2" ></constructor-arg>
</bean>                           

<bean name="car" class="cn.itcast.entity.Car" p:name="布加迪威航">
</bean>

</beans>