ibatis对枚举类的支持

àì夳堔傛蜴生んèń 2022-01-14 19:37 210阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

前一段时间和同事争论枚举类是否该出现在pojo类中，当时出现了分歧。因为项目中使用ibatis，我认为枚举类在get、set方法中需要进行特殊处理，破坏了原有的pojo纯净。后来我发现我错了：pojo类中可以存放，并且最好使用枚举。

### pojo类 ###

package com.sg.bean;
    
    public class User {
    
        /**
         * 用户ID
         */
        private String userID;
        
        /**
         * 用户名 
         */
        private String userName;
        
        /**
         * 用户状态
         * @see com.sg.bean.EnumStatus
         */
        private EnumStatus status;
        
        public String getUserID() {
            return userID;
        }
        public void setUserID(String userID) {
            this.userID = userID;
        }
        public String getUserName() {
            return userName;
        }
        public void setUserName(String userName) {
            this.userName = userName;
        }
        public EnumStatus getStatus() {
            return status;
        }
        public void setStatus(EnumStatus status) {
            this.status = status;
        }
    }

### 枚举类 ###

package com.sg.bean;
    
    public enum EnumStatus {
    
        NORMAL("1", "正常"),
        DELETE("2", "删除"),
        LOGICDEL("3", "注销");
        
        private EnumStatus(String code, String description) {
            this.code = code;
            this.description = description;
        }
        private String code;
        
        private String description;
    
        public String getCode() {
            return code;
        }
    
        public void setCode(String code) {
            this.code = code;
        }
    
        public String getDescription() {
            return description;
        }
    
        public void setDescription(String description) {
            this.description = description;
        }
    }

### 重点来了——ibatis类型转换接口实现 ###

#### 先看一下源码中的注释 ####

com.ultrapower.common.ibatis.sqlmap.client.extensions.TypeHandlerCallback
 A simple interface for implementing custom type handlers. 
 
 Using this interface, you can implement a type handler that will perform customized processing before parameters are set on a PreparedStatement and after values are retrieved from a ResultSet. Using a custom type handler you can extend the framework to handle types that are not supported, or handle supported types in a different way. For example, you might use a custom type handler to implement proprietary BLOB support (e.g. Oracle), or you might use it to handle booleans using "Y" and "N" instead of the more typical 0/1. 
 
 EXAMPLE 
 
 Here's a simple example of a boolean handler that uses "Yes" and "No". 
 
 
 public class YesNoBoolTypeHandlerCallback implements TypeHandlerCallback {
 
 private static final String YES = "Yes";
 private static final String NO = "No";
 
 public Object getResult(ResultGetter getter) throws SQLException {
 String s = getter.getString();
 if (YES.equalsIgnoreCase(s)) {
 return new Boolean (true);
 } else if (NO.equalsIgnoreCase(s)) {
 return new Boolean (false);
 } else {
 throw new SQLException ("Unexpected value " + s + " found where "+YES+" or "+NO+" was expected.");
 }
 }
 
 public void setParameter(ParameterSetter setter, Object parameter) throws SQLException {
 boolean b = ((Boolean)parameter).booleanValue();
 if (b) {
 setter.setString(YES);
 } else {
 setter.setString(NO);
 }
 }
 
 public Object valueOf(String s) {
 if (YES.equalsIgnoreCase(s)) {
 return new Boolean (true);
 } else if (NO.equalsIgnoreCase(s)) {
 return new Boolean (false);
 } else {
 throw new SQLException ("Unexpected value " + s + " found where "+YES+" or "+NO+" was expected.");
 }
 }
 
 }

#### 针对User对象中的EnumStatus，他的转换类如下 ####

package com.sg.util;
    
    import java.sql.SQLException;
    import java.sql.Types;
    
    import com.ibatis.sqlmap.client.extensions.ParameterSetter;
    import com.ibatis.sqlmap.client.extensions.ResultGetter;
    import com.ibatis.sqlmap.client.extensions.TypeHandlerCallback;
    import com.sg.bean.EnumStatus;
    
    public class EnumStatusHandler implements TypeHandlerCallback {
    
        public Object getResult(ResultGetter getter) throws SQLException {
            EnumStatus result = null;
            if(!getter.wasNull() && getter.getObject()!= null) {
                for(EnumStatus status : EnumStatus.values()) {
                    if(status.getCode().equals(getter.getObject())) {
                        result = status;
                        break;
                    }
                }
            }
            return result;
        }
    
        public void setParameter(ParameterSetter setter, Object obj)
                throws SQLException {
            if(obj == null) {
                setter.setInt(Types.INTEGER);
            }else {
                EnumStatus status = (EnumStatus)obj;
                setter.setString(status.getCode());
            }
        }
    
        public Object valueOf(String s) {
            return s;
        }
    
    }

### ibatis配置文件声明 ###

<?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE sqlMapConfig 
 PUBLIC "-//iBATIS.com//DTD SQL Map Config 2.0//EN" "http://ibatis.apache.org/dtd/sql-map-config-2.dtd">
 <sqlMapConfig>
 	<settings cacheModelsEnabled="true" enhancementEnabled="true"
 		lazyLoadingEnabled="true" errorTracingEnabled="true" maxRequests="32"
 		maxSessions="10" maxTransactions="5" useStatementNamespaces="false" />
 		
 	<typeAlias alias="com.sg.bean.EnumStatus" type="com.sg.util.EnumStatusHandler"/>
 	
 	<transactionManager type="JDBC">
 		<dataSource type="SIMPLE">
 			<property name="JDBC.Driver" value="com.mysql.jdbc.Driver" />
 			<property name="JDBC.ConnectionURL"
 				value="jdbc:mysql://localhost:3306/sg" />
 			<property name="JDBC.Username" value="root" />
 			<property name="JDBC.Password" value="root" />
 			<property name="Pool.MaximumIdleConnections" value="5" />
 			<property name="Pool.MaximumCheckoutTime" value="120000" />
 			<property name="Pool.TimeToWait" value="500" />
 			<property name="Pool.PingQuery"
 				value="select 1 from sample" />
 			<property name="Pool.PingEnabled" value="false" />
 			<property name="Pool.PingConnectionsOlderThan" value="1" />
 			<property name="Pool.PingConnectionsNotUsedFor" value="1" />
 		</dataSource>
 	</transactionManager>
 	
 	<sqlMap resource="User.xml" />
 </sqlMapConfig>

经过上述的配置，User对象中的EnumStatus枚举类就可以顺利的进行数据库操作了，以上方案有以下几个好处：

1.  没有破坏pojo的纯净，pojo对象的扩展和可维护性更高；
2.  枚举类加强了User对象对属性类型的把控，开发这不用担心其他人在status属性中放错值了；
3.  pojo的扩展性增强，比如现在前台展示需要展示名称，开发者只需对枚举进行简单的读取就可以将数据库中的0、1转为自然语言；
4.  脱离实体的限制，比如前台需要展示status的可选值，枚举类便可以首当其冲。

转载于:https://my.oschina.net/SEyanlei/blog/179926

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220114/115bde1b102c49cf931657054e1d921e.png