SqlSessionFactory的创建
SqlSessionFactory是通过SqlSessionFactoryBuilder工厂类创建的，而不是直接使用构造器。
SqlSessionFactoryBuilder的主要代码如下:
//SqlSessionFactoryBuilder是一个建造者模式
public SqlSessionFactory build(InputStream inputStream) {
return build(inputStream, null, null);
}
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
try {
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
inputStream.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
SqlSessionFactory提供了根据字节流、字符流以及直接使用org.apache.ibatis.session.Configuration配置类（后续我们会详细讲到）三种途径的读取配置信息方式，但究其根本都是首先将XML配置文件构建为Configuration配置类，然后将Configuration设置到SqlSessionFactory默认实现DefaultSqlSessionFactory的configurationz字段并返回。主要解析配置文件的逻辑都委托给XMLConfigBuilder了。
XMLConfigBuilder的主要代码
public class XMLConfigBuilder extends BaseBuilder {
....
/**
* Description 构造XMLConfigBuilder
* @param reader 流
* @param environment
* @param props
* @author songhongwei s19744
* @time 202/1/5 16:44
**/
public XMLConfigBuilder(Reader reader, String environment, Properties props) {
//XPathParser用于SAX解析xml，解析器硬编码为XMLMapperEntityResolver
this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
}
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
//创建Configuration对象,用来保存配置文件的配置
super(new Configuration());
ErrorContext.instance().resource("SQL Mapper Configuration");
this.configuration.setVariables(props);
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
....
}
标签解析类
public class XPathParser {
private final Document document;
private boolean validation;
//XML标签解析器,可使用不通的解析器,通过构造方法传进来,使用到了策略模式
private EntityResolver entityResolver;
private Properties variables;
private XPath xpath;
/**
* Description 构造方法
*
* @param reader
* Reader
* @param validation
* 是否进行DTD 校验
* @param variables
* 属性配置
* @param entityResolver
* XML实体节点解析器
* @author songhongwei s19744
* @time 202/1/5 19:54
**/
public XPathParser(Reader reader, boolean validation, Properties variables, EntityResolver entityResolver) {
commonConstructor(validation, variables, entityResolver);
this.document = createDocument(new InputSource(reader));
}
//创建document
private Document createDocument(InputSource inputSource) {
// important: this must only be called AFTER common constructor
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
factory.setValidating(validation);
factory.setNamespaceAware(false);
factory.setIgnoringComments(true);
factory.setIgnoringElementContentWhitespace(false);
factory.setCoalescing(false);
factory.setExpandEntityReferences(true);
DocumentBuilder builder = factory.newDocumentBuilder();
builder.setEntityResolver(entityResolver);
builder.setErrorHandler(new ErrorHandler() {
@Override
public void error(SAXParseException exception) throws SAXException {
throw exception;
}
@Override
public void fatalError(SAXParseException exception) throws SAXException {
throw exception;
}
@Override
public void warning(SAXParseException exception) throws SAXException {
// NOP
}
});
return builder.parse(inputSource);
} catch (Exception e) {
throw new BuilderException("Error creating document instance. Cause: " + e, e);
}
}
}
XMLConfigBuilder以及解析Mapper文件的XMLMapperBuilder都继承于BaseBuilder。他们对于XML文件本身技术上的加载和解析都委托给了XPathParser，最终用的是jdk自带的xml解析器而非第三方比如dom4j，底层使用了xpath方式进行节点解析。new XPathParser(reader, true, props, new XMLMapperEntityResolver())的参数含义分别是Reader，是否进行DTD 校验，属性配置，XML实体节点解析器。
entityResolver，跟Spring的XML标签解析器一样，有默认的解析器，也有自定义的，主要使用了策略模式，在这里mybatis硬编码为XMLMapperEntityResolver。
XMLMapperEntityResolver的定义如下：
package org.apache.ibatis.builder.xml;
import org.apache.ibatis.io.Resources;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import java.io.IOException;
import java.io.InputStream;
import java.util.Locale;
/**
* Offline entity resolver for the MyBatis DTDs.
*
* @author Clinton Begin
* @author Eduardo Macarron
*/
public class XMLMapperEntityResolver implements EntityResolver {
private static final String IBATIS_CONFIG_SYSTEM = "ibatis-3-config.dtd";
private static final String IBATIS_MAPPER_SYSTEM = "ibatis-3-mapper.dtd";
private static final String MYBATIS_CONFIG_SYSTEM = "mybatis-3-config.dtd";
private static final String MYBATIS_MAPPER_SYSTEM = "mybatis-3-mapper.dtd";
private static final String MYBATIS_CONFIG_DTD = "org/apache/ibatis/builder/xml/mybatis-3-config.dtd";
private static final String MYBATIS_MAPPER_DTD = "org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd";
/**
* Converts a public DTD into a local one. 将公共的DTD转换为本地模式
* @param publicId The public id that is what comes after "PUBLIC"
* @param systemId The system id that is what comes after the public id.
* @return The InputSource for the DTD
* @throws org.xml.sax.SAXException If anything goes wrong
*/
@Override
public InputSource resolveEntity(String publicId, String systemId) throws SAXException {
try {
if (systemId != null) {
String lowerCaseSystemId = systemId.toLowerCase(Locale.ENGLISH);
if (lowerCaseSystemId.contains(MYBATIS_CONFIG_SYSTEM) || lowerCaseSystemId.contains(IBATIS_CONFIG_SYSTEM)) {
return getInputSource(MYBATIS_CONFIG_DTD, publicId, systemId);
} else if (lowerCaseSystemId.contains(MYBATIS_MAPPER_SYSTEM) || lowerCaseSystemId.contains(IBATIS_MAPPER_SYSTEM)) {
return getInputSource(MYBATIS_MAPPER_DTD, publicId, systemId);
}
}
return null;
} catch (Exception e) {
throw new SAXException(e.toString());
}
}
private InputSource getInputSource(String path, String publicId, String systemId) {
InputSource source = null;
if (path != null) {
try {
InputStream in = Resources.getResourceAsStream(path);
source = new InputSource(in);
source.setPublicId(publicId);
source.setSystemId(systemId);
} catch (IOException e) {
// ignore, null is ok
}
}
return source;
}
}
mybatis解析的时候，引用了本地的DTD文件，和本类在同一个package下，其中的ibatis-3-config.dtd应该主要是用于兼容用途。在其中getInputSource(MYBATIS_CONFIG_DTD, publicId, systemId)的调用里面有两个参数publicId（公共标识符）和systemId（系统标示符），他们是XML 1.0规范的一部分，在mybatis中，systemId指定的是mybatis-3-config.dtd和ibatis-3-config.dtd
调用栈
build:64, SqlSessionFactoryBuilder (org.apache.ibatis.session)
-->build:77, SqlSessionFactoryBuilder (org.apache.ibatis.session)
--><init>:89, XMLConfigBuilder (org.apache.ibatis.builder.xml)
--><init>:127, XPathParser (org.apache.ibatis.parsing)
-->createDocument:261, XPathParser (org.apache.ibatis.parsing)
-->parse:339, DocumentBuilderImpl (com.sun.org.apache.xerces.internal.jaxp)
-->parse:243, DOMParser (com.sun.org.apache.xerces.internal.parsers)
-->parse:141, XMLParser (com.sun.org.apache.xerces.internal.parsers)
-->parse:771, XML11Configuration (com.sun.org.apache.xerces.internal.parsers)
-->parse:842, XML11Configuration (com.sun.org.apache.xerces.internal.parsers)
-->scanDocument:505, XMLDocumentFragmentScannerImpl (com.sun.org.apache.xerces.internal.impl)
-->next:602, XMLDocumentScannerImpl (com.sun.org.apache.xerces.internal.impl)
-->next:959, XMLDocumentScannerImpl$PrologDriver (com.sun.org.apache.xerces.internal.impl)
-->next:1045, XMLDocumentScannerImpl$DTDDriver (com.sun.org.apache.xerces.internal.impl)
-->dispatch:1151, XMLDocumentScannerImpl$DTDDriver (com.sun.org.apache.xerces.internal.impl)
-->resolveEntityAsPerStax:997, XMLEntityManager (com.sun.org.apache.xerces.internal.impl)
-->resolveEntity:110, EntityResolverWrapper (com.sun.org.apache.xerces.internal.util)
-->resolveEntity:58, XMLMapperEntityResolver (org.apache.ibatis.builder.xml)