【Java从0到架构师】Spring - 复杂对象、Converter

骑猪看日落 2022-09-02 13:58 146阅读 0赞

### 复杂对象、Converter ###

*  创建过程比较复杂的对象
 *   *  实例工厂
     *  静态工厂
     *  FactroyBean
     *  引入外部配置文件
     *  SpEL表达式
     *  scope - 控制 bean 是否单例
 *  Converter
 *   *  Spring 内置基本的类型转换功能
     *  自定义 Converter

> Java 从 0 到架构师目录：[【Java从0到架构师】学习记录][Java_0]

> 学习 Spring 搭配这门课效果更好：[《孙哥说Spring5》学习笔记][Spring5]

Gitee 代码：[https://gitee.com/szluyu99/mj\_java\_frame/tree/master/02\_Spring/][https_gitee.com_szluyu99_mj_java_frame_tree_master_02_Spring]

# 创建过程比较复杂的对象 #

> [【Spring 工厂】反转控制与依赖注入、Spring工厂创建复杂对象3种方式][Spring _Spring_3]

## 实例工厂 ##

public class ConnectionFactory { 
    	public Connection getConn1() throws Exception { 					
    		Class.forName("com.mysql.jdbc.Driver");
    		return DriverManager.getConnection("x", "x", "x");
    	}
    }

<bean id="factory" class="com.mj.obj.ConnectionFactory"/>
    <bean id="conn1" factory-bean="factory" factory-method="getConn1"/>

## 静态工厂 ##

public class ConnectionFactory { 
        public static Connection getConn2() throws Exception { 
            Class.forName("com.mysql.jdbc.Driver");
            return DriverManager.getConnection("x", "x", "x");
        }
    }

<bean id="conn2" class="com.mj.obj.ConnectionFactory" factory-method="getConn2"/>

## FactroyBean ##

public class ConnectionFactoryBean implements FactoryBean<Connection> { 
    	@Override
    	public Connection getObject() throws Exception { 
    		Class.forName("com.mysql.jdbc.Driver");
            return DriverManager.getConnection("x", "x", "x");
    	}
    	
    	@Override
    	public Class<?> getObjectType() { 
    		return Connection.class;
    	}
    }

// & 开头代表创建的是FactoryBean类型的对象
    // 参考: BeanFactory中的FACTORY_BEAN_PREFIX
    System.out.println(ctx.getBean("&conn"))

## 引入外部配置文件 ##

# db.properties
    jdbc.driverClass=com.mysql.jdbc.Driver
    jdbc.url=jdbc:mysql://localhost:3306/test_mybatis
    jdbc.username=root
    jdbc.password=root

首先在 applicationContext.xml 根标签中引入标签库：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczNDA5NQ_size_16_color_FFFFFF_t_70]

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" 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 http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    
    
    <context:property-placeholder location="db.properties"/>
    
    
    <bean id="conn" class="com.mj.obj.ConnectionFactoryBean">
        <property name="driverClass" value="${jdbc.driverClass}"/>
        <property name="url" value="${jdbc.url}"/>
        
        <property name="username" value="${jdbc.username}"/>
        <property name="password" value="${jdbc.password}"/>
    </bean>

## SpEL表达式 ##

> 参考资料：[https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html\#expressions][https_docs.spring.io_spring_docs_current_spring-framework-reference_core.html_expressions]

## scope - 控制 bean 是否单例 ##

> 参考资料：[https://docs.spring.io/spring-framework/docs/current/reference/html/core.html\#beans-factory-scopes][https_docs.spring.io_spring-framework_docs_current_reference_html_core.html_beans-factory-scopes]

`scope="singleton"`：单例

*  通过同一个 id 值，在统一 IoC 容器中获取的永远是同一个实例
 *  在 IoC 容器创建的时候，就会创建 bean，可以设置 `lazy-init="true"` 修改创建时机

`scope="prototype"`：非单例；每次 getBaen 时创建一次 bean

# Converter #

> [【Spring5.x】对象的生命周期、配置文件参数化、自定义类型转换器、后置处理Bean][Spring5.x_Bean]

## Spring 内置基本的类型转换功能 ##

Spring 已经内置了基本的类型转换功能，比如：

*  String 转 int
 *  String 转 Date（支持 **yyyy/MM/dd** 格式）

## 自定义 Converter ##

实现 Converter 接口：

public class DateConverter implements Converter<String, Date> { 
        private List<String> formats;
        public void setFormats(List<String> formats) { 
            this.formats = formats;
        }
    
        @Override
        public Date convert(String s) { 
        	try { 
                return new SimpleDateFormat(format).parse(s);
            } catch (ParseException e) { 
                e.printStackTrace();
                return null;
            }
        }
    }

> 注：id 为 conversionService 是固定的

--------------------

进阶示例：在 xml 中传入 list 的类设计

实现 Converter 接口：

public class DateConverter implements Converter<String, Date> { 
        private List<String> formats;
        public void setFormats(List<String> formats) { 
            this.formats = formats;
        }
    
        @Override
        public Date convert(String s) { 
            for (String format : formats) { 
                try { 
                    SimpleDateFormat fmt = new SimpleDateFormat(format);
                    return fmt.parse(s);
                } catch (ParseException e) { 
                    // e.printStackTrace();
                }
            }
            return null;
        }
    }

[Java_0]: https://blog.csdn.net/weixin_43734095/article/details/119067034
[Spring5]: https://blog.csdn.net/weixin_43734095/article/details/106309373
[https_gitee.com_szluyu99_mj_java_frame_tree_master_02_Spring]: https://gitee.com/szluyu99/mj_java_frame/tree/master/02_Spring/
[Spring _Spring_3]: https://blog.csdn.net/weixin_43734095/article/details/106292604
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczNDA5NQ_size_16_color_FFFFFF_t_70]: /images/20220829/2fb3b9daad7a411e81fb8f77943a55f8.png
[https_docs.spring.io_spring_docs_current_spring-framework-reference_core.html_expressions]: https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#expressions_
[https_docs.spring.io_spring-framework_docs_current_reference_html_core.html_beans-factory-scopes]: https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans-factory-scopes
[Spring5.x_Bean]: https://blog.csdn.net/weixin_43734095/article/details/106308703