Spring之依赖注入

分析

依赖注入是Spring框架核心IOC的具体体现。

方式

构造方法

需要在A类里边声明有参构造方法和无参构造方法

package com.itheima.service.impl;

import com.itheima.dao.UserDao;
import com.itheima.service.UserService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class UserServiceImpl implements UserService {
    public UserServiceImpl(UserDao userDao) {
        this.userDao = userDao;
    }
    public UserServiceImpl() {
    }

    @Override
    public void save() {
        userDao.save();
    }
}

Spring配置文件中引用B类

<bean id="userDao" class="com.itheima.dao.impl.UserDaoImpl"/>  
<bean id="userService" class="com.itheima.service.impl.UserServiceImpl">
    <constructor-arg name="userDao" ref="userDao"></constructor-arg>
</bean>

set方法

假设A类需要调用B类，那么A类中需要有一个B类的set方法，同时在Spring配置文件中，A类Bean使用property标签来引用B类Bean。

package com.itheima.service.impl;

import com.itheima.dao.UserDao;
import com.itheima.service.UserService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class UserServiceImpl implements UserService {

    private UserDao userDao;
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
    
    
    @Override
    public void save() {
        userDao.save();
    }
}

<!--    因为UserService和UserDao都在Spring容器中，而最终程序直接使用的是UserService，所以可以在Spring容器中，将UserDao设置到UserService内部-->
<!--    使用set方法向Service注入Dao-->
<bean id="userDao" class="com.itheima.dao.impl.UserDaoImpl"/>    
<bean id="userService" class="com.itheima.service.impl.UserServiceImpl">
<!--        name属性：set方法名去掉set，然后首字母小写-->
<!--        ref属性：引用Dao的Bean标签的id-->
        <property name="userDao" ref="userDao"/>
    </bean>

userService的Bean还可以使用p标签来引入userDao

需要事先声明命名空间：xmlns:p="http://www.springframework.org/schema/p"

<bean id="userService" class="com.itheima.service.impl.UserServiceImpl" p:userDao-ref="userDao"/>

数据注入

普通数据类型

使用property标签进行值的传入，实体类需要存在set方法与get方法，接收传入值的类需要set方法。

package com.itheima.entity;

public class User {
    private String name;
    private String addr;

    public String getName() {
        return name;
    }

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

    public String getAddr() {
        return addr;
    }

    public void setAddr(String addr) {
        this.addr = addr;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", addr='" + addr + '\'' +
                '}';
    }
}

<bean id="userDao" class="com.itheima.dao.impl.UserDaoImpl">
    <property name="username" value="Jack"></property>
    <property name="age" value="23"></property>
</bean>

引用数据类型

不再赘述

集合数据类型

类似于普通数据类型，接收传入值的类需要存在set方法

package com.itheima.dao.impl;

import com.itheima.dao.UserDao;
import com.itheima.entity.User;

import java.util.List;
import java.util.Map;
import java.util.Properties;

public class UserDaoImpl implements UserDao {
    private List<String> strList;
    private Map<String, User> userMap;
    private Properties properties;

    public void setStrList(List<String> strList) {
        this.strList = strList;
    }

    public void setUserMap(Map<String, User> userMap) {
        this.userMap = userMap;
    }

    public void setProperties(Properties properties) {
        this.properties = properties;
    }

    public void save() {
        //System.out.println(username+ "=====" + age);
        System.out.println(strList);
        System.out.println(userMap);
        System.out.println(properties);
        System.out.println("save running....");
    }
}

<bean id="userDao" class="com.itheima.dao.impl.UserDaoImpl">
    <property name="strList">
        <list>
            <value>aaa</value>
            <value>bbb</value>
            <value>ccc</value>
        </list>
    </property>
    <property name="userMap">
        <map>
            <entry key="u1" value-ref="user1"/>
            <entry key="u2" value-ref="user2"/>
        </map>
    </property>
    <property name="properties">
        <props>
            <prop key="p1">ppp1</prop>
            <prop key="p2">ppp2</prop>
            <prop key="p3">ppp3</prop>
        </props>
    </property>
</bean>

<!--user1和user2为map服务-->
<bean id="user1" class="com.itheima.entity.User">
    <property name="name" value="tom"></property>
    <property name="addr" value="beijing"></property>
</bean>
<bean id="user2" class="com.itheima.entity.User">
    <property name="name" value="jack"></property>
    <property name="addr" value="tianjin"></property>
</bean>