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在以前文章中,咱们把 Mybatis 源码浏览的整个流程梳理了一遍。明天,咱们来具体聊聊,Mybatis 是如何解析配置文件的。
这是明天剖析的流程图:
还是从案例开始。
demo 案例
public static void main(String[] args) {
String resource = "mybatis-config.xml";
InputStream inputStream = null;
SqlSession sqlSession = null;
try {inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
sqlSession = sqlSessionFactory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
System.out.println(userMapper.selectById(1));
} catch (Exception e) {e.printStackTrace();
} finally {
try {inputStream.close();
} catch (IOException e) {e.printStackTrace();
}
sqlSession.close();}
}
见证奇观
从 SqlSessionFactoryBuilder
开始。
SqlSessionFactoryBuilder 类
org.apache.ibatis.session.SqlSessionFactoryBuilder
该类里全是 build 办法各种重载。
// 这个办法啥也没干
public SqlSessionFactory build(InputStream inputStream) {return build(inputStream, null, null);
}
最终来到另外一个 build 办法里:
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
try {
// 创立一个 XMLConfigBuilder 对象
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.}
}
}
XMLConfigBuilder 类
该类的构造方法重载:
首先进入:
public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment,
props);
}
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {super(new Configuration());
ErrorContext.instance().resource("SQL Mapper Configuration");
this.configuration.setVariables(props);
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
build(parser.parse()); 中的 parser.parse();
mybatis-config.xml 在哪里解析的呢?
请看上面这个办法:
// 该办法返回一个 Configuration 对象
public Configuration parse() {if (parsed) {throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
// 关键点
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
parseConfiguration(parser.evalNode("/configuration"));
终于看到开始解析配置文件了:
进入办法 parseConfiguration。
private void parseConfiguration(XNode root) {
try {
//issue #117 read properties first
propertiesElement(root.evalNode("properties"));
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// read it after objectFactory and objectWrapperFactory issue #631
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {throw new BuilderException("Error parsing SQL Mapper Configuration. Cause:" + e, e);
}
}
这里就是把 mybatis-config.xml 内容解析,而后设置到 Configuration 对象中。
那么咱们定义的 Mapper.xml 是在哪里解析的呢?
咱们的 Mapper.xml 在 mybatis-config.xml 中的配置是这样的:
<mapper>
应用形式有以下四种:
// 1 应用类门路
<mappers>
<mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
<mapper resource="org/mybatis/builder/BlogMapper.xml"/>
<mapper resource="org/mybatis/builder/PostMapper.xml"/>
</mappers>
// 2 应用相对 url 门路
<mappers>
<mapper url="file:///var/mappers/AuthorMapper.xml"/>
<mapper url="file:///var/mappers/BlogMapper.xml"/>
<mapper url="file:///var/mappers/PostMapper.xml"/>
</mappers>
// 3 应用 java 类名
<mappers>
<mapper class="org.mybatis.builder.AuthorMapper"/>
<mapper class="org.mybatis.builder.BlogMapper"/>
<mapper class="org.mybatis.builder.PostMapper"/>
</mappers>
// 4 主动扫描包下所有映射器
<mappers>
<package name="org.mybatis.builder"/>
</mappers>
持续源码剖析,咱们在下面 mybatis-config.xml 解析中能够看到:
咱们无妨进入这个办法看看:
private void mapperElement(XNode parent) throws Exception {if (parent != null) {for (XNode child : parent.getChildren()) {
// 主动扫描包下所有映射器
if ("package".equals(child.getName())) {String mapperPackage = child.getStringAttribute("name");
// 放
configuration.addMappers(mapperPackage);
} else {String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
// 应用 java 类名
if (resource != null && url == null && mapperClass == null) {ErrorContext.instance().resource(resource);
// 依据文件寄存目录,读取 XxxMapper.xml
InputStream inputStream = Resources.getResourceAsStream(resource);
// 映射器比较复杂,调用 XMLMapperBuilder
// 留神在 for 循环里每个 mapper 都从新 new 一个 XMLMapperBuilder,来解析
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
mapperParser.parse();
// 应用相对 url 门路
} else if (resource == null && url != null && mapperClass == null) {ErrorContext.instance().resource(url);
InputStream inputStream = Resources.getUrlAsStream(url);
// 映射器比较复杂,调用 XMLMapperBuilder
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
mapperParser.parse();
// 应用类门路
} else if (resource == null && url == null && mapperClass != null) {Class<?> mapperInterface = Resources.classForName(mapperClass);
// 间接把这个映射退出配置
configuration.addMapper(mapperInterface);
} else {throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}
这里刚刚和咱们的下面说的 <mapper>
应用的形式齐全是截然不同的。
到这里,配置文件 mybatis-config.xml 和咱们定义映射文件 XxxMapper.xml 就全副解析实现。
回到 SqlSessionFactoryBuilder 类
后面讲到了 XMLConfigBuilder 中的 parse 办法,并返回了一个 Configuration 对象。
build(parser.parse());
这个 build 办法就是传入一个 Configuration 对象,而后构建一个 DefaultSqlSession 对象。
public SqlSessionFactory build(Configuration config) {return new DefaultSqlSessionFactory(config);
}
持续回到咱们的 demo 代码中这一行代码里:
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
这一行代码就相当于:
SqlSessionFactory sqlSessionFactory = new new DefaultSqlSessionFactory();
到这里,咱们的整个流程就搞定了。
举荐浏览
Mybatis 中 xml 和注解映射,so easy 啦