Spring根据XML配置文件注入对象类型属性_springboot xml 注入对象构造器参数对象类型-优快云博客

本文链接：https://blog.youkuaiyun.com/swift2010/article/details/78944228

本文介绍如何在Spring中通过XML配置文件来创建对象并注入对象类型的属性，以降低组件间的耦合。讨论了在DAO、Service和Servlet中的应用，并提供了一个因忘记更新setter方法名称导致的错误案例及解决方案。

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这里有dao、service和Servlet三个地方

通过配过文件xml生成对象，并注入对象类型的属性，降低耦合

dao文件代码：

package com.swift;

public class DaoUser {
    public void fun() {
        System.out.println("I'm  dao's fun()....................");
    }
}

service文件代码：（提供setter方法，xml文件可通过这种方法配置）

package com.swift;

public class ServiceUser {
    private DaoUser daoUser;
    
    public void setDaoUser(DaoUser daoUser) {
        this.daoUser = daoUser;
    }

    public String fun() {
        System.out.println("I am Service's fun()..............");
        return daoUser.fun();
    }
}

xml文件代码：

<?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 Spring根据XML配置文件注入对象类型属性 -->
<bean id="dao" class="com.swift.DaoUser"></bean>
<bean id="service" class="com.swift.ServiceUser">
<property name="daoUser" ref="dao"></property>
</bean>
</beans>

Servlet类文件可以绕开dao的文件，直接使用service即可

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("/duixiang")
public class ServletService extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public ServletService() {
        super();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().append("Served at: ").append(request.getContextPath());
        @SuppressWarnings("resource")
        ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");
        ServiceUser service=(ServiceUser) context.getBean("service");
        response.getWriter().append(service.fun());
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

中间因修改属性名字，而忽略修改setter方法名字导致出错，已改好，错误的类型记录了一下：

Caused by: org.springframework.beans.NotWritablePropertyException: Invalid property 'daoUser' of bean class [com.swift.ServiceUser]: Bean property 'daoUser' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?
提示的很好，要不自己很难发现。