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在以前文章中，我们把Mybatis源码阅读的整个流程梳理了一遍。今天，我们来详细聊聊，Mybatis是如何解析配置文件的。
这是今天分析的流程图：
还是从案例开始。
demo案例
-
public static void main(String[] args) {
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String resource =
"mybatis-config.xml";
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InputStream inputStream = null;
-
SqlSession sqlSession = null;
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try {
-
inputStream = Resources.getResourceAsStream(resource);
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SqlSessionFactory sqlSessionFactory =
new SqlSessionFactoryBuilder().build(inputStream);
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sqlSession = sqlSessionFactory.openSession();
-
-
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
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System.out.
println(userMapper.selectById(
1));
-
-
} catch (Exception e) {
-
e.printStackTrace();
-
} finally {
-
try {
-
inputStream.
close();
-
} catch (IOException e) {
-
e.printStackTrace();
-
}
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sqlSession.
close();
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}
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}
-
见证奇迹
从SqlSessionFactoryBuilder开始。
SqlSessionFactoryBuilder类
org.apache.ibatis.session.SqlSessionFactoryBuilder
该类里全是build方法各种重载。
-
//这个方法啥也没干
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public SqlSessionFactory build(InputStream inputStream) {
-
return build(inputStream, null, null);
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}
最终来到另外一个build方法里：
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public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
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try {
-
//创建一个XMLConfigBuilder对象
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XMLConfigBuilder parser =
new XMLConfigBuilder(inputStream, environment, properties);
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return build(parser.parse());
-
} catch (Exception e) {
-
throw ExceptionFactory.wrapException(
"Error building SqlSession.", e);
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} finally {
-
ErrorContext.instance().reset();
-
try {
-
inputStream.
close();
-
} catch (IOException e) {
-
// Intentionally ignore. Prefer previous error.
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}
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}
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}
XMLConfigBuilder类
该类的构造方法重载：
首先进入：
-
public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
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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");
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this.configuration.setVariables(props);
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this.parsed =
false;
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this.environment = environment;
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this.parser = parser;
-
}
build(parser.parse());中的parser.parse()；
mybatis-config.xml在哪里解析的呢？
请看下面这个方法：
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//该方法返回一个Configuration对象
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public Configuration parse() {
-
if (parsed) {
-
throw
new BuilderException(
"Each XMLConfigBuilder can only be used once.");
-
}
-
parsed =
true;
-
//关键点
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parseConfiguration(parser.evalNode(
"/configuration"));
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return configuration;
-
}
parseConfiguration(parser.evalNode("/configuration"));
终于看到开始解析配置文件了:
进入方法parseConfiguration。
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private void parseConfiguration(XNode root) {
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try {
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//issue #117 read properties first
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propertiesElement(root.evalNode(
"properties"));
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Properties settings = settingsAsProperties(root.evalNode(
"settings"));
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loadCustomVfs(settings);
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loadCustomLogImpl(settings);
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typeAliasesElement(root.evalNode(
"typeAliases"));
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pluginElement(root.evalNode(
"plugins"));
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objectFactoryElement(root.evalNode(
"objectFactory"));
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objectWrapperFactoryElement(root.evalNode(
"objectWrapperFactory"));
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reflectorFactoryElement(root.evalNode(
"reflectorFactory"));
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settingsElement(settings);
-
// read it after objectFactory and objectWrapperFactory issue #631
-
environmentsElement(root.evalNode(
"environments"));
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databaseIdProviderElement(root.evalNode(
"databaseIdProvider"));
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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，然后设置到Configuration对象中。
那么我们定义的Mapper.xml是在哪里解析的呢？
我们的Mapper.xml在mybatis-config.xml中的配置是这样的：
<mapper>使用方式有以下四种：
-
//1使用类路径
-
<mappers>
-
<mapper resource=
"org/mybatis/builder/AuthorMapper.xml"/>
-
<mapper resource=
"org/mybatis/builder/BlogMapper.xml"/>
-
<mapper resource=
"org/mybatis/builder/PostMapper.xml"/>
-
</mappers>
-
//2使用绝对url路径
-
<mappers>
-
<mapper url=
"file:///var/mappers/AuthorMapper.xml"/>
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<mapper url=
"file:///var/mappers/BlogMapper.xml"/>
-
<mapper url=
"file:///var/mappers/PostMapper.xml"/>
-
</mappers>
-
//3使用java类名
-
<mappers>
-
<mapper class=
"org.mybatis.builder.AuthorMapper"/>
-
<mapper class=
"org.mybatis.builder.BlogMapper"/>
-
<mapper class=
"org.mybatis.builder.PostMapper"/>
-
</mappers>
-
-
//4自动扫描包下所有映射器
-
<mappers>
-
<
package name=
"org.mybatis.builder"/>
-
</mappers>
继续源码分析，我们在上面mybatis-config.xml解析中可以看到：
我们不妨进入这个方法看看：
-
private void mapperElement(XNode parent) throws Exception {
-
if (parent != null) {
-
for (XNode child : parent.getChildren()) {
-
//自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");
-
//使用java类名
-
if (resource != null && url == null && mapperClass == null) {
-
ErrorContext.instance().resource(resource);
-
//根据文件存放目录，读取XxxMapper.xml
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InputStream inputStream = Resources.getResourceAsStream(resource);
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//映射器比较复杂，调用XMLMapperBuilder
-
//注意在for循环里每个mapper都重新new一个XMLMapperBuilder，来解析
-
XMLMapperBuilder mapperParser =
new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
-
mapperParser.parse();
-
//使用绝对url路径
-
}
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();
-
//使用类路径
-
}
else
if (resource == null && url == null && mapperClass != null) {
-
Class<?> mapperInterface = Resources.classForName(mapperClass);
-
//直接把这个映射加入配置
-
configuration.addMapper(mapperInterface);
-
}
else {
-
throw
new BuilderException(
"A mapper element may only specify a url, resource or class, but not more than one.");
-
}
-
}
-
}
-
}
-
}
这里刚刚和我们的上面说的<mapper>使用的方式完全是一模一样的。
到这里，配置文件mybatis-config.xml和我们定义映射文件XxxMapper.xml就全部解析完成。
回到SqlSessionFactoryBuilder类
前面讲到了XMLConfigBuilder中的parse方法，并返回了一个Configuration对象。
build(parser.parse());
这个build方法就是传入一个Configuration对象，然后构建一个DefaultSqlSession对象。
-
public SqlSessionFactory build(Configuration config) {
-
return
new DefaultSqlSessionFactory(config);
-
}
继续回到我们的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，我们的整个流程就搞定了。
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转载：https://blog.csdn.net/o9109003234/article/details/111306443
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