IBatis入门

iBatis 简介：

iBatis 是apache 的一个开源项目，一个O/R Mapping 解决方案，iBatis 最大的特点就是小巧，上手很快。如果不需要太多复杂的功能，iBatis 是能够满足你的要求又足够灵活的最简单的解决方案，现在的iBatis 已经改名为Mybatis 了。

官网为：http://www.mybatis.org/

二、iBatis的工作原理与流程

 iBatis使用简单的xml描述文件将JavaBean，Map实现和基本数据类型的包装类（String，Integer等）映射成JDBC的PreparedStatement的输入参数和ResultSet结果集，流程如下：

   1、在sqlMapConfig的XML配置文件中进行数据库连接的配置，XML配置文件名称任意，比如SqlMapConfig.xml

   2、在sqlMapConfig的XML配置文件中引用sqlMap的XML配置文件

　　<sqlMap resource="User.xml"/>

　　<sqlMap url="file://User.xml"/>

3、在sqlMap的XML配置文件中进行SQL的配置，文件名称任意

4、通过SqlMapClientBuilder生成具体的操作sqlMap配置文件中的SQL文的ibatis对象SqlMapClient

　　String resource="SqlMapConfig.xml"

　　Reader reader=Resources.getResourceAsReader(resource);

　　SqlMapClient  sqlMap=SqlMapClientBuilder.buildSqlMapClient(reader);

5、SqlMapClient对象提供函数，函数的参数对应替换sqlMap配置文件中的id，parameter等属性，完成SQL文的执行。

　　public List queryForList(String statementName, Object parameterObject, int skipResults, int maxResults)

　　statement：SqlMap配置中id属性，parameterObject：sqlMap配置中parameter###属性

搭建iBatis 开发环境：

1 、创建工程，导入相关的jar 包，ibatis.jar 、mysql.jar

2 、编写配置文件：

总属性文件：application-global.properties

总配置文件：SqlMapConfig.xml

每个实体的映射文件（Map 文件）：User.xml

application-global.properties

driverClass=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/ibatis
username=root
password=123456

SqlMapConfig.xml

<?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>

    <!-- 引用JDBC属性的配置文件 -->
    <properties resource="application-global.properties" />

    <!-- 默认配置 -->
    <settings cacheModelsEnabled="true" enhancementEnabled="true"
        lazyLoadingEnabled="true" errorTracingEnabled="true" maxRequests="32"
        maxSessions="10" maxTransactions="5" useStatementNamespaces="false" />

    <!-- 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">
        <dataSource type="SIMPLE">
            <property name="JDBC.Driver" value="${driverClass}" />
            <property name="JDBC.ConnectionURL" value="${url}" />
            <property name="JDBC.Username" value="${username}" />
            <property name="JDBC.Password" value="${password}" />
        </dataSource>
    </transactionManager>

    <!-- 这里可以写多个实体的映射文件 -->
    <sqlMap resource="User.xml" />

</sqlMapConfig>  

User.xml

<?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="user">

    <typeAlias alias="User" type="org.apache.ibatis.bo.User" />
    
    <insert id="insertUser" parameterClass="User">
        insert into user values (#id#,#name#,#sex#)
    </insert>
    
    <delete id="deleteById" parameterClass="int">
         delete from user where id=#id#
    </delete>
    
    <update id="updateUser" parameterClass="User">
         update user set name=#name#,sex=#sex# where id=#id#
    </update>
    
    <select id="queryById" parameterClass="int" resultClass="User">
         select * from user where id=#id#
    </select>
    
    <select id="queryAllUsers" resultClass="User">
         select * from user
    </select>
</sqlMap>

User.java

package org.apache.ibatis.bo;

import java.io.Serializable;
import java.util.List;

public class User implements Serializable {
    
    /**
     * 
     */
    private static final long serialVersionUID = -5560728144383386239L;

    int id;
    String name;
    int sex;
    List<Role> roles;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public int getSex() {
        return sex;
    }

    public void setSex(int sex) {
        this.sex = sex;
    }

    public List<Role> getRoles() {
        return roles;
    }

    public void setRoles(List<Role> roles) {
        this.roles = roles;
    }

    @Override
    public String toString() {
        return "id=" + id + ",name=" + name + ",sex=" + sex;
    }
}

IbatisUtils.java

package org.apache.ibatis.util;

import java.io.IOException;
import java.io.Reader;
import java.sql.SQLException;
import java.util.List;

import org.apache.ibatis.bo.User;

import com.ibatis.common.resources.Resources;
import com.ibatis.sqlmap.client.SqlMapClient;
import com.ibatis.sqlmap.client.SqlMapClientBuilder;

/**
 * This is not a best practices class. It's just an example to give you an idea
 * of how iBATIS works. For a more complete example, see JPetStore 5.0 at
 * http://www.ibatis.com.
 */
public class IBatisUtils {

    /**
     * SqlMapClient instances are thread safe, so you only need one. In this
     * case, we'll use a static singleton. So sue me. ;-)
     */
    private static SqlMapClient sqlMapper;

    /**
     * It's not a good idea to put code that can fail in a class initializer,
     * but for sake of argument, here's how you configure an SQL Map.
     */
    static {
        try {
            Reader reader = Resources.getResourceAsReader("SqlMapConfig.xml");
            sqlMapper = SqlMapClientBuilder.buildSqlMapClient(reader);
            reader.close();
        } catch (IOException e) {
            // Fail fast.
            throw new RuntimeException(
                    "Something bad happened while building the SqlMapClient instance."
                            + e.getMessage(), e);
        }
    }

    public static void createUser(String paramString) throws SQLException {
        sqlMapper.update(paramString, null);
    }

    public static void dropUser(String paramString) throws SQLException {
        sqlMapper.update(paramString, null);
    }

    public static List<?> queryAllUsers(String paramString) throws SQLException {
        return sqlMapper.queryForList(paramString);
    }

    public static User selectUserById(String paramString, int id)
            throws SQLException {
        return (User) sqlMapper.queryForObject(paramString, id);
    }

    public static void insertUser(String paramString, User user)
            throws SQLException {
        sqlMapper.insert(paramString, user);
    }

    public static void updateUser(String paramString, User user)
            throws SQLException {
        sqlMapper.update(paramString, user);
    }

    public static void deleteUser(String paramString, int id)
            throws SQLException {
        sqlMapper.delete(paramString, id);
    }

}

Main.java

package org.apache.ibatis.test;

import java.sql.SQLException;
import java.util.Arrays;
import java.util.List;

import org.apache.ibatis.bo.User;
import org.apache.ibatis.util.IBatisUtils;

public class Main {

    public void insertUser() throws SQLException {
        User user = new User();
        user.setId(0);
        user.setName("张三");
        user.setSex(1);
        IBatisUtils.insertUser("insertUser", user);
        System.out.println("insert success!, user = " + user);
    }

    private void queryAllUsers() throws SQLException {
        List<?> list = IBatisUtils.queryAllUsers("queryAllUsers");
        for (int i = 0; i < list.size(); i++) {
            User user = (User) list.get(i);
            System.out.println(user);
        }
        System.out.println(Arrays.toString(list.toArray()));
    }

    public static void main(String[] args) {
        Main main = new Main();
        try {
            main.queryAllUsers();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

}

至此，测试结束

FAQ:

1、com.ibatis.sqlmap.client.SqlMapException: There is already a statement named xxx in this SqlMap.

Exception in thread "main" java.lang.ExceptionInInitializerError
    at org.apache.ibatis.data.Main.selectAllAccounts(Main.java:23)
    at org.apache.ibatis.data.Main.main(Main.java:59)
Caused by: java.lang.RuntimeException: Error occurred.  
Cause: com.ibatis.common.xml.NodeletException: Error parsing XML.  Cause: java.lang.RuntimeException: Error parsing XPath '/sqlMapConfig/sqlMap'.  Cause: com.ibatis.common.xml.NodeletException: Error parsing XML.  Cause: java.lang.RuntimeException: Error parsing XPath '/sqlMap/select'.  
Cause: com.ibatis.sqlmap.client.SqlMapException: There is already a statement named selectById in this SqlMap.
    at com.ibatis.sqlmap.engine.builder.xml.SqlMapConfigParser.parse(SqlMapConfigParser.java:89)
    at com.ibatis.sqlmap.client.SqlMapClientBuilder.buildSqlMapClient(SqlMapClientBuilder.java:63)
    at org.apache.ibatis.data.IBatisUtils.<clinit>(IBatisUtils.java:35)
    ... 2 more

这个是因为存在相同的SQL ID

解决方案如下：

<!-- 启用命名空间 -->
<settings useStatementNamespaces="true" />

useStatementNamespaces
如果启用本属性，必须使用全限定名来引用 mapped useStatementNamespaces statement。

Mapped statement 的全限定名由 sql-map 的名称和 mapped-statement 的名称合成。例如： queryForObject("sqlMapName.statementName");
缺省值：false（禁用）

2、org.xml.sax.SAXParseException: The content ofelement type “sqlMapConfig” must match“(properties?,settings?,resultObjectFactory?,ypeAlias*,typeHandler*,transactionManager?,sqlMap+)+”

Exception in thread "main" java.lang.ExceptionInInitializerError
    at org.apache.ibatis.data.Main.selectAllAccounts(Main.java:23)
    at org.apache.ibatis.data.Main.main(Main.java:59)
Caused by: java.lang.RuntimeException: Error occurred.  Cause: com.ibatis.common.xml.NodeletException: Error parsing XML.  Cause: org.xml.sax.SAXParseException: The content of element type "sqlMapConfig" must match "(properties?,settings?,resultObjectFactory?,typeAlias*,typeHandler*,transactionManager?,sqlMap+)+".
    at com.ibatis.sqlmap.engine.builder.xml.SqlMapConfigParser.parse(SqlMapConfigParser.java:89)
    at com.ibatis.sqlmap.client.SqlMapClientBuilder.buildSqlMapClient(SqlMapClientBuilder.java:63)
    at org.apache.ibatis.data.IBatisUtils.<clinit>(IBatisUtils.java:35)
    ... 2 more
Caused by: com.ibatis.common.xml.NodeletException: Error parsing XML.  Cause: org.xml.sax.SAXParseException: The content of element type "sqlMapConfig" must match "(properties?,settings?,resultObjectFactory?,typeAlias*,typeHandler*,transactionManager?,sqlMap+)+".
    at com.ibatis.common.xml.NodeletParser.parse(NodeletParser.java:53)
    at com.ibatis.sqlmap.engine.builder.xml.SqlMapConfigParser.parse(SqlMapConfigParser.java:86)
    ... 4 more
Caused by: org.xml.sax.SAXParseException: The content of element type "sqlMapConfig" must match "(properties?,settings?,resultObjectFactory?,typeAlias*,typeHandler*,transactionManager?,sqlMap+)+".
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:195)
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.error(ErrorHandlerWrapper.java:131)
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:384)
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:318)
    at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.handleEndElement(XMLDTDValidator.java:2017)
    at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.endElement(XMLDTDValidator.java:901)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1782)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2939)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:647)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:511)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:808)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:119)
    at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:232)
    at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:284)
    at com.ibatis.common.xml.NodeletParser.createDocument(NodeletParser.java:157)
    at com.ibatis.common.xml.NodeletParser.parse(NodeletParser.java:50)
    ... 5 more

这个是因为ibatis配置文件sqlMapConfig的属性是有顺序的，配置顺序properties,settings,resultObjectFactory,typeAlias*,typeHandler*,transactionManager,sqlMap 。

附录：

1、SqlMapConfig.xml中的setting属性

<settings
cacheModelsEnabled="true"
lazyLoadingEnabled="false"
enhancementEnabled="true"
maxSessions="64"
maxTransactions="8"
maxRequests="128"
useStatementNamespaces="false"
classInfoCacheEnabled="true"
errorTracingEnabled="true"
defaultStatementTimeout=""
statementCachingEnabled="true"
/>
<!--
maxRequests
同时执行 SQL 语句的最大线程数。大于这个值的线程将阻塞直到另一个线程执行完成。不同的 DBMS有不同的限制值，但任何数据库都有这些限制。通常这个值应该至少是maxTransactions（参见以下）的 10 倍，并且总是大于 maxSessions 和maxTranactions。减小这个参数值通常能提高性能。

例如：maxRequests=“256”
缺省值：512

maxSessions
同一时间内活动的最大 session 数。一个 session 可以maxSessions是代码请求的显式 session，也可以是当线程使用SqlMapClient 实例（即执行一条语句）自动获得的session。它应该总是大于或等于 maxTransactions 并小于 maxRequests。减小这个参数值通常能减少内存使用。

例如：maxSessions=“64”
缺省值：128

maxTransactions
同时进入 SqlMapClient.startTransaction()的最大线程maxTransactions 数。大于这个值的线程将阻塞直到另一个线程退出。不同的 DBMS 有不同的限制值，但任何数据库都有这些限制。这个参数值应该总是小于或等于maxSessions 并总是远远小于 maxRequests。减小这个参数值通常能提高性能。

例如：maxTransactions=“16”
缺省值：32

cacheModelsEnabled
全局性地启用或禁用 SqlMapClient 的所有缓存cacheModelsEnabled model。调试程序时使用。

例如：cacheModelsEnabled=“true”
缺省值：true（启用）

lazyLoadingEnabled
全局性地启用或禁用SqlMapClient的所有延迟加载。lazyLoadingEnabled 调试程序时使用。
例子：lazyLoadingEnabled=“true”
缺省值：true（启用）

enhancementEnabled
全局性地启用或禁用运行时字节码增强，以优化访enhancementEnabled
问Java Bean属性的性能，同时优化延迟加载的性能。

例子：enhancementEnabled=“true”
缺省值：false（禁用）

useStatementNamespaces
如果启用本属性，必须使用全限定名来引用 mapped useStatementNamespaces
statement。Mapped statement 的全限定名由 sql-map 的名称和 mapped-statement 的名称合成。例如： queryForObject("sqlMapName.statementName");

例如：useStatementNamespaces=“false”
缺省值：false（禁用）

defaultStatementTimeout
此设置值必须为一个整数，作为JDBC连接超时的时间，这个值可以被任意一个映射文件的statement属性来重新设置，
如果没有指明，查询将无超时时间限制除非在映射文件中设置statement属性值。被设置的值以秒为单位等待连接失效

classInfoCacheEnabled 
With this setting enabled, iBATIS will maintain a cache of introspected
classes. This will lead to a significant reduction in startup time if many
classes are reused.
例如: classInfoCacheEnabled=“true”
缺省值: true (启用)

statementCachingEnabled (iBATIS 2.3.0以后版本中有)
With this setting enabled, iBATIS will maintain a local cache of
prepared statements. This can lead to significant performance
improvements.
例如: statementCachingEnabled=“true”
缺省值: true (启用)