一、<environments>元素的結構
在Mybatis-config.xml中,<environments>元素的配置方式如下所示:
<environments default="mysql">
<environment id="mysql">
<transactionManager type="JDBC" />
<!-- 配置數據庫連接信息 -->
<dataSource type="POOLED">
<property name="driver" value="${driver}" />
<property name="url" value="${url}" />
<property name="username" value="${username}" />
<property name="password" value="${password?:123456}" />
<property name="driver.encoding" value="UTF8"/>
</dataSource>
</environment>
</environments>
從定義config配置文件文檔結構的文件mybatis-3-config.dtd中<environments>元素相關約束可以看出<environments>元素可以允許的結構:
- <environments>元素可以出現一次或者零次
- <environments>元素必須有 屬性default
- <environments>元素必須有一個或者多個<environment>子元素
- <environment>元素必須有屬性id
- <environment>元素下必須有且只有一個<transactionManager>和<dataSource>子元素
- <transactionManager>元素必須有一個type屬性
- <transactionManager>元素可以有零或多個<property>元素
- <dataSource>元素必須有一個type屬性
- <dataSource>元素可以有零或多個<property>元素
<!ELEMENT configuration (properties?, settings?, typeAliases?, typeHandlers?, objectFactory?, objectWrapperFactory?, reflectorFactory?, plugins?, environments?, databaseIdProvider?, mappers?)>
<!ELEMENT environments (environment+)>
<!ATTLIST environments
default CDATA #REQUIRED
>
<!ELEMENT environment (transactionManager,dataSource)>
<!ATTLIST environment
id CDATA #REQUIRED
>
<!ELEMENT transactionManager (property*)>
<!ATTLIST transactionManager
type CDATA #REQUIRED
>
<!ELEMENT dataSource (property*)>
<!ATTLIST dataSource
type CDATA #REQUIRED
>
關於DTD相關知識請參考《XML DTD》
二、<environments>元素初始化時解析的入口
environmentsElement()方法用來解析<environments>元素,其中包括瞭解析<transactionManager>和<dataSource>子元素的方法。然後通過Environment的內部構建器類Builder來構建Environment實例,然後把構建的Environment實例,賦值到了configuration配置類的environment屬性中,便於後期使用。這個時候就完成了初始化解析的工作了。
/**
* 解析配置文件中的environments元素
* @param context
* @throws Exception
*/
private void environmentsElement(XNode context) throws Exception {
if (context != null) {
if (environment == null) {
environment = context.getStringAttribute("default");
}
for (XNode child : context.getChildren()) {//解析environment元素
String id = child.getStringAttribute("id");
if (isSpecifiedEnvironment(id)) {//判斷是否是默認配置,即environments元素的default屬性值。比如:<environments default="development">
//解析事務管理器
TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
//解析數據源
DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
DataSource dataSource = dsFactory.getDataSource();
//構建environment對象
Environment.Builder environmentBuilder = new Environment.Builder(id)
.transactionFactory(txFactory)
.dataSource(dataSource);
//賦值到configuration的對應屬性中
configuration.setEnvironment(environmentBuilder.build());
}
}
}
}
transactionManagerElement()方法用來解析<transactionManager>元素。
/**
* 解析事務管理器對象
* @param context
* @return
* @throws Exception
*/
private TransactionFactory transactionManagerElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
Properties props = context.getChildrenAsProperties();
TransactionFactory factory = (TransactionFactory) resolveClass(type).newInstance();
factory.setProperties(props);
return factory;
}
throw new BuilderException("Environment declaration requires a TransactionFactory.");
}
dataSourceElement()方法用來解析<dataSource>元素。
/**
* 解析數據源元素
* @param context
* @return
* @throws Exception
*/
private DataSourceFactory dataSourceElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
Properties props = context.getChildrenAsProperties();
DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
factory.setProperties(props);
return factory;
}
throw new BuilderException("Environment declaration requires a DataSourceFactory.");
}
三、Transaction、DataSource相關類型
在Mybatis中針對事務、數據源都分別進行了封裝,具體請參考以下文檔: