iBatis2学习笔记:基本原理和配置
iBatis2是一个轻量级的数据持久化框架,它是一个半自动化的ORMapping工具,数据库的操作依赖程序员自己书写的SQL,因此可以最大限度发挥JDBC的性能。据测试,它的性能和JDBC是一个级别的,但代码比JDBC简单的多,据说相对JDBC节省了60%的代码量。
缺点是映射不灵活,有时候感觉很别扭。当领域对象关系复杂的时候,关联基本上行不通。
iBatis2整个框架的jar包就一个,337KB,相比Hibernate等其他框架非常的小巧可爱,并且有.net语言版本。
iBatis2的优缺点不是关心的重点,主要是在实际中扬长避短。下面是iBatis2的框架图:
和Hibernate的SessionFactory类似,iBatis2有SqlMapClientBuilder一个类,通过配置文件SqlMapConfig.xml类构建,这个是线程安全的类,并且是单例模式,从它里面可以获取SqlMapClient,SqlMapClient相当于Hibernate的session,用来执行预定义的SQL语句。
因此SqlMapClientBuilder、SqlMapConfig.xml、SqlMapClient将是学习iBatis2的核心。以后会逐渐展开,下面是从变成角度来构建SqlMapClientBuilder。
String resource ="SqlMapConfig.xml";
Reader reader = Resources.getResourceAsReader(resource);
SqlMapClient sqlMap = SqlMapClientBuilder.buildSqlMapClient(reader);
由于SqlMapClientBuilder的构建是相当耗时的,因此一般都是在程序启动的时候构建一次,并反复使用。
SqlMapClient 是线程不安全的,每次用的时候,需要从SqlMapClientBuilder去申请一个。它相当于一个数据库连接。
下面给出一个我学习的例子,也是iBatis中自带的一个例子,但是这个例子无法正常运行,主要是数据库、驱动还有模糊的配置概念导致。下面详细讲述如何规范的把这个例子跑起来:
环境:
MySQL5、Java5、iBatis2.3
一、下载iBatis:[url]http://ibatis.apache.org/javadownloads.cgi[/url];
下载MySQL5和MySQL5的JDBC驱动:[url]http://dev.mysql.com/downloads/mysql/5.0.html[/url],[url]http://dev.mysql.com/downloads/connector/j/5.1.html[/url]
下载SQLyog Enterprise 6.5,这是MySQL的客户端工具,[url]http://www.fixdown.com/china/Programming/109.htm[/url]
二、安装MySQL5,下载MySQL5,解压缩到某一目录下,然后修改my-small.ini文件如下:
然后安装并启动MySQL5服务
安装MySQL的客户端工具,SQLyog Enterprise 6.5
三、在Idea8中创建一个Java工程ibatis_stu
引入两个必须的包,如下图:
数据库链接配置文件 jdbc.properties:
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ibatisdb
jdbc.username=root
jdbc.password=leizhimin
构件要操作表:
create table ACCOUNT(
ACC_ID bigint not null AUTO_INCREMENT,
ACC_FIRST_NAME varchar(20) default NULL,
ACC_LAST_NAME varchar(30) default NULL,
ACC_EMAIL varchar(30) default NULL,
PRIMARY KEY(ACC_ID)
) ENGINE=MyISAM DEFAULT CHARSET=gbk COMMENT='IBATIS简单测试'
iBaits的配置文件SqlMapConfig.xml,(为了使用一些高级特性,增加了命名空间等配置,同时导入了jdbc.properties来协助配置)
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE sqlMapConfig PUBLIC "-//ibatis.apache.org//DTD SQL Map Config 2.0//EN" "http://ibatis.apache.org/dtd/sql-map-config-2.dtd"> <sqlMapConfig> <properties resource="jdbc.properties"/> <settings cacheModelsEnabled="true" errorTracingEnabled="true" enhancementEnabled="true" lazyLoadingEnabled="true" maxRequests="32" maxSessions="10" maxTransactions="5" useStatementNamespaces="true"/> <!-- Configure a built-in transaction manager. If you're using an app server, you probably want to use its transaction manager and a managed datasource --> <transactionManager type="JDBC" commitRequired="false"> <dataSource type="SIMPLE"> <property name="JDBC.Driver" value="${jdbc.driver}"/> <property name="JDBC.ConnectionURL" value="${jdbc.url}"/> <property name="JDBC.Username" value="${jdbc.username}"/> <property name="JDBC.Password" value="${jdbc.password}"/> </dataSource> </transactionManager> <!-- List the SQL Map XML files. They can be loaded from the classpath, as they are here (com.domain.data...) --> <sqlMap resource="com/lavasoft/ibatissut/simple/domain/entity/Account.xml"/> <!-- List more here...--> </sqlMapConfig>
嵌入的Account的表与实体映射代码:
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE sqlMap PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN" "http://ibatis.apache.org/dtd/sql-map-2.dtd"> <sqlMap namespace="Account"> <!-- Use type aliases to avoid typing the full classname every time. --> <typeAlias alias="Account" type="com.lavasoft.ibatissut.simple.domain.entity.Account"/> <!-- Result maps describe the mapping between the columns returned from a query, and the class properties. A result map isn't necessary if the columns (or aliases) match to the properties exactly. --> <resultMap id="AccountResult" class="Account"> <result property="id" column="ACC_ID"/> <result property="firstName" column="ACC_FIRST_NAME"/> <result property="lastName" column="ACC_LAST_NAME"/> <result property="emailAddress" column="ACC_EMAIL"/> </resultMap> <!-- Select with no parameters using the result map for Account class. --> <select id="selectAllAccounts" resultMap="AccountResult"> select * from ACCOUNT </select> <!-- A simpler select example without the result map. Note the aliases to match the properties of the target result class. --> <select id="selectAccountById" parameterClass="int" resultClass="Account"> select ACC_ID as id, ACC_FIRST_NAME as firstName, ACC_LAST_NAME as lastName, ACC_EMAIL as emailAddress from ACCOUNT where ACC_ID = #id# </select> <!-- Insert example, using the Account parameter class --> <insert id="insertAccount" parameterClass="Account"> insert into account(ACC_ID,ACC_FIRST_NAME,ACC_LAST_NAME,ACC_EMAIL) values(NULL, #firstName#, #lastName#, #emailAddress#) </insert> <!-- Update example, using the Account parameter class --> <update id="updateAccount" parameterClass="Account"> update ACCOUNT set ACC_FIRST_NAME = #firstName#, ACC_LAST_NAME = #lastName#, ACC_EMAIL = #emailAddress# where ACC_ID = #id# </update> <!-- Delete example, using an integer as the parameter class --> <delete id="deleteAccountById" parameterClass="int"> delete from ACCOUNT where ACC_ID = #id# </delete> </sqlMap>
一个与表对应的实体Bean(为了输出重写了toString方法):
package com.lavasoft.ibatissut.simple.domain.entity; /** * Created by IntelliJ IDEA.<p> * User: leizhimin<p> * Date: 2008-8-16 9:57:03<p> * 帐户 */ public class Account { private int id; private String firstName; private String lastName; private String emailAddress; public Account() { } public Account(String firstName, String lastName, String emailAddress) { this.firstName = firstName; this.lastName = lastName; this.emailAddress = emailAddress; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getEmailAddress() { return emailAddress; } public void setEmailAddress(String emailAddress) { this.emailAddress = emailAddress; } @Override public String toString() { return "Account{" + "id=" + id + ", firstName='" + firstName + '\'' + ", lastName='" + lastName + '\'' + ", emailAddress='" + emailAddress + '\'' + '}'; } }
核心测试代码(尊重iBatis的原版风格,就窝下蛋,写个main方法就开始跑了。。):
package com.lavasoft.ibatissut.simple; import com.ibatis.sqlmap.client.SqlMapClient; import com.ibatis.sqlmap.client.SqlMapClientBuilder; import com.ibatis.common.resources.Resources; import com.lavasoft.ibatissut.simple.domain.entity.Account; import java.io.Reader; import java.io.IOException; import java.util.List; import java.sql.SQLException; /** * Created by IntelliJ IDEA.<p> * User: leizhimin<p> * Date: 2008-8-16 9:59:10<p> * 首先声明这不是最好的例子,但是从这个例子中可以很快的了解iBatis的工作原理, * 如果需要更好的学习iBatis,可以参看iBatis实现的JPetStore-5.0.zip。 * [url]http://apache.mirror.phpchina.com/ibatis/binaries/ibatis.java/JPetStore-5.0.zip[/url] */ public class SimpleExample { /** * SqlMapClient的实例是线程安全的,因此仅需要一个实例即可,这里使用了一个静态单例模式。 */ private static SqlMapClient sqlMapClient; /** * 将SqlMapClient的构件放到此不是好注意,应该放到一个单例模式的工具类中,需要的时候随时获取 */ static { try { //读取SqlMapConfig的资源配置 Reader reader = Resources.getResourceAsReader("SqlMapConfig.xml"); //构件一个SqlMapClient的实例 sqlMapClient = SqlMapClientBuilder.buildSqlMapClient(reader); //关闭输入流 reader.close(); } catch (IOException e) { throw new RuntimeException("在构件SqlMapClient实例的时候发生了异常!" + e, e); } } public static List selectAllAccounts() throws SQLException { //返回所有的帐户 return sqlMapClient.queryForList("Account.selectAllAccounts"); } public static Account selectAccountById(int id) throws SQLException { return (Account) sqlMapClient.queryForObject("Account.selectAccountById", id); } public static void insertAccount(Account account) throws SQLException { sqlMapClient.insert("Account.insertAccount", account); } public static void updateAccount(Account account) throws SQLException { sqlMapClient.update("Account.updateAccount", account); } public static void deleteAccount(int id) throws SQLException { sqlMapClient.delete("Account.deleteAccount", id); } public static void main(String[] args) throws SQLException { Account act = new Account("1","1","1"); act.setId(23); insertAccount(act); List<Account> acclist= selectAllAccounts(); for(Account acc:acclist){ System.out.println(acc); } } }
运行一把看看:
Account{id=1, firstName='45', lastName='45', emailAddress='4554'}
Account{id=2, firstName='234', lastName='234', emailAddress='23423'}
Account{id=3, firstName='1', lastName='1', emailAddress='1'}
Account{id=4, firstName='1', lastName='1', emailAddress='1'}
Account{id=5, firstName='1', lastName='1', emailAddress='1'}
Process finished with exit code 0
呵呵,终于看到效果了。
iBatis是个好东西,但是技巧性很强,只有完全掌握了iBatis的映射原理和技巧,用起来才不至于生硬繁琐重复。上面这个例子是iBatis发布包中唯一一个例子,而且使用的是一个大家都很陌生的数据库,并且没有执行的入口方法,缺乏SQL脚本,没有使用命名空间等等,这个粗糙的例子给很多第一次接触iBatis的人一个极坏的印象,和一些致命的误导。
iBatis应用中应该使用命名空间,不使用的话好像除了HelloWorld这样的简单例子外,找不到第二个。