iBATIS Data Mapper 2.3 Developer Guide

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"iBATIS Data Mapper 2.3 开发指南" iBATIS Data Mapper，又称SQL Maps，是一个轻量级的持久层框架，它在2.3版本中提供了更加强大和灵活的数据访问功能。这份文档是针对iBATIS Data Mapper 2.3的开发者指南，旨在帮助开发者更好地理解和使用这个框架。 1. **简介** iBATIS Data Mapper的核心理念是将SQL映射到Java对象，从而简化数据库操作。这个框架允许开发者将SQL语句直接写在XML配置文件中，与Java代码分离，增强了代码的可维护性和可读性。 2. **安装** 安装过程通常涉及将iBATIS库添加到项目的类路径中。开发者需要下载iBATIS的jar文件，并将其包含在项目的构建路径中，或者通过Maven或Gradle等依赖管理工具来添加依赖。 3. **从1.x升级** 升级到2.3版本可能涉及到一些API和配置的变动。开发者应仔细阅读升级指南，确保所有旧的SQL Maps能够正确地工作在新版本上。 4. **XML配置文件** iBATIS的核心配置文件包括`<sqlMapConfig.xml>`，它定义了数据源、事务管理器、类型别名、属性等关键元素。其中： - **<properties>** 元素用于加载外部属性文件，提供配置参数。 - **<settings>** 允许开发者调整iBATIS的行为，如开启或关闭缓存。 - **<resultObjectFactory>** 指定结果对象工厂，用于创建结果集对象。 - **<typeAlias>** 用于给Java类定义简短的名字，方便在XML配置中引用。 - **<transactionManager>** 和 **<dataSource>** 分别定义事务管理和数据源配置。 - **<sqlMap>** 用于包含具体的SQL映射文件。 5. **SQL Map XML文件** SQL Map XML文件包含了具体的SQL语句和映射规则。它定义了`<select>`, `<insert>`, `<update>`, `<delete>`等元素，以及`<parameterMap>`和`<resultMap>`来处理输入参数和输出结果。 6. **Mapped Statements** Mapped Statements是SQL Maps的核心，它们定义了如何执行SQL语句以及如何处理返回的结果。 7. **Statement Types** 包括了动态SQL（基于条件拼接SQL）、自动生成主键、存储过程支持等功能。 8. **参数映射和内联参数** `ParameterMaps`用于映射Java对象到SQL的参数，而内联参数则允许在SQL语句中直接使用Java对象的属性。 9. **结果映射** `ResultMaps`定义了如何将查询结果映射到Java对象，包括基本类型、复杂类型以及集合类型的映射。 10. **缓存** iBATIS支持缓存机制，可以缓存MappedStatement的结果，提高性能。开发者可以通过配置来启用和控制缓存行为。 11. **自定义Type Handlers** 当iBATIS内置的类型处理器无法满足需求时，开发者可以创建自定义的Type Handlers来处理特定的数据类型。 12. **避免N+1 Selects问题** iBATIS提供了优化策略，通过一次查询获取关联数据，防止多次数据库查询导致的性能问题。 13. **支持的类型** iBATIS支持多种Java类型作为参数和结果，包括基本类型、复杂对象、集合等。 iBATIS Data Mapper 2.3提供了丰富的功能，使开发者能够灵活地处理SQL与Java对象之间的映射，同时通过配置和缓存机制来优化性能。对于任何需要与关系型数据库交互的Java应用，它都是一个强大的选择。

Developer Guide iBATIS Data Mapper 2.3

the object through its normal means (class.newInstance()). If you return null from a request to create

java.util.Collection or java.util.List, then iBATIS will create

java.util.ArrayList. If you return null from a request to create java.util.Set, then iBATIS

will create java.util.HashSet. iBATIS passes the current statement id to let you know the context in

which the object create is requested.

The <typeAlias> Element

The typeAlias element simply allows you to specify a shorter name to refer to what is usually a long, fully

qualified classname. For example:

There are some predefined aliases used in the SQL Map Config file. They are:

Transaction Manager Aliases

JDBC

JTA

EXTERNAL

com.ibatis.sqlmap.engine.transaction.jdbc.JdbcTransactionConfig

com.ibatis.sqlmap.engine.transaction.jta.JtaTransactionConfig

com.ibatis.sqlmap.engine.transaction.external.ExternalTransactionConfig

Data Source Factory Aliases

SIMPLE

DBCP

JNDI

com.ibatis.sqlmap.engine.datasource.SimpleDataSourceFactory

com.ibatis.sqlmap.engine.datasource.DbcpDataSourceFactory

com.ibatis.sqlmap.engine.datasource.JndiDataSourceFactory

The <transactionManager> Element

1.0 Conversion Note: Data Mapper 1.0 allowed multiple datasources to be configured. This became

cumbersome and introduced some bad practices. Therefore 2.0 only allows a single datasource. For

multiple deployments/configurations it is recommended that you use multiple properties files that are

either configured differently by the system, or passed in as a parameter when building the SQL Map (see

the java API section below).

The <transactionManager> element allows you to configure the transaction management services for an

SQL Map. The type attribute indicates which transaction manager to use. The value can either be a class

name or a type alias. The three transaction managers included with the framework are: JDBC, JTA and

EXTERNAL.

JDBC - This allows JDBC to control the transaction via the usual Connection commit() and

rollback() methods.

JTA - This transaction manager uses a JTA global transaction such that the SQL Map activities can

be included as part of a wider scope transaction that possibly involves other databases or

transactional resources. This configuration requires a UserTransaction property set to locate the

user transaction from a JNDI resource. See the JNDI datasource example below for an example of

this configuration.

EXTERNAL – This allows you to manage transactions on your own. You can still configure a

data source, but transactions will not be committed or rolled back as part of the framework

lifecycle. This means that some part of your application external to Data Mapper must manage the

transactions. This setting is also useful for non-transactional databases (e.g. Read-only).

The <transactionManager> element also allows an optional attribute commitRequired that can be true or

false. Normally iBATIS will not commit transactions unless an insert, update, or delete operation has been

performed. This is true even if you explicitly call the commitTransaction() method. This behavior

creates problems in some cases. If you want iBATIS to always commit transactions, even if no insert,

http://ibatis.apache.org by Clinton Begin

Developer Guide iBATIS Data Mapper 2.3

update, or delete operation has been performed, then set the value of the commitRequired attribute to true.

Examples of where this attribute is useful include:

1. If you call a stored procedures that updates data as well as returning rows. In that case you would

call the procedure with the queryForList() operation – so iBATIS would not normally commit the

transaction. But then the updates would be rolled back.

2. In a WebSphere environment when you are using connection pooling and you use the JNDI

<dataSource> and the JDBC or JTA transaction manager. WebSphere requires all transactions on

pooled connections to be committed or the connection will not be returned to the pool.

Note that the commitRequired attribute has no effect when using the EXTERNAL transaction manager.

Some of the transaction managers allow extra configuration properties. The following table shows extra

properties that are available for the various transaction managers:

Transaction

Manager

Properties

EXTERNAL

Property Description

DefaultAutoCommit If “true”, then setAutoCommit(true) will be called on the

underlying connection for each transaction if that is not the

value supplied by the underlying datasource.

If “false” or unspecified, then setAutoCommit(false) will be

called on the underlying connection for each transaction if

that is not the value supplied by the underlying datasource.

This behavior can be overridden with the

“SetAutoCommitAllowed” property.

SetAutoCommitAllowed If “true” or unspecified, then the behavior specified in the

“DefaultAutoCommit” property will occur.

If “false”, then iBATIS will not call setAutoCommit in any

case – this is useful in environments like WebSphere where

the setAutoCommit method should not be called in any

circumstance.

JTA

Property Description

UserTransaction This property is required.

The value of the user transaction. Note that in many cases

this should be set to “java:comp/UserTransaction”

The <dataSource> Element

Included as part of the transaction manager configuration is a dataSource element and a set of properties to

configure a DataSource for use with your SQL Map. There are currently three datasource factories

provided with the framework, but you can also write your own. The included DataSourceFactory

implementations are discussed in further detail below and example configurations are provided for each.

http://ibatis.apache.org by Clinton Begin

Developer Guide iBATIS Data Mapper 2.3

SimpleDataSourceFactory

The SimpleDataSource factory provides a basic implementation of a pooling DataSource that is

ideal for providing connections in cases where there is no container provided DataSource. It is

based on the iBATIS SimpleDataSource connection pool implementation.

<property name="JDBC.ConnectionURL"

value="jdbc:postgresql://server:5432/dbname"/>

</dataSource>

</transactionManager>

Note that any property prefixed with “Driver.” will be added as a property to the underlying JDBC

driver.

DbcpDataSourceFactory

This implementation uses Jakarta DBCP (Database Connection Pool) to provide connection

pooling services via the DataSource API. This DataSource is ideal where the application/web

container cannot provide a DataSource implementation, or you’re running a standalone

application. IBATIS provides direct access to setting the properties of a DBCP datasource by

allowing you to specify any DBCP property name you desire in the configuration. For example:

<!-- Use of the validation query can be problematic.

If you have difficulty, try without it. -->

</datasource>

</transactionManager>

http://ibatis.apache.org by Clinton Begin

Developer Guide iBATIS Data Mapper 2.3

You can see all available properties here:

http://jakarta.apache.org/commons/dbcp/configuration.html

Note that any property prefixed with “Driver.” will be added as a property to the underlying JDBC

driver as shown above.

iBATIS also supports a less flexible legacy configuration option as show below. However, we

recommend that you use the configuration option shown above.

<!-- Use of the validation query can be problematic.

If you have difficulty, try without it. -->

</datasource>

</transactionManager>

The properties shown are the only properties recognized by iBATIS when using the legacy

configuration option. Note that any property prefixed with “Driver.” will be added as a property to

the underlying JDBC driver as shown above.

JndiDataSourceFactory

This implementation will retrieve a DataSource implementation from a JNDI context from within

an application container. This is typically used when an application server is in use and a

container managed connection pool and associated DataSource implementation are provided. The

standard way to access a JDBC DataSource implementation is via a JNDI context.

JndiDataSourceFactory provides functionality to access such a DataSource via JNDI. The

configuration parameters that must be specified in the datasource stanza are as follows:

</dataSource>

</transactionManager>

The above configuration will use normal JDBC transaction management. But with a container

managed resource, you might also want to configure it for global transactions as follows:

</dataSource>

</transactionManager>

Notice the UserTransaction property that points to the JNDI location where the UserTransaction

instance can be found. This is required for JTA transaction management so that your SQL Map

take part in a wider scoped transaction involving other databases and transactional resources.

http://ibatis.apache.org by Clinton Begin

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iBATIS Data Mapper 2.3 Developer Guide

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