代码版本：3.4.2
public static void main(String[] args) throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
//入口
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
Employee employeeMapper = sqlSession.getMapper(Employee.class);
List<Employee> all = employeeMapper.getAll();
for (Employee item : all)
System.out.println(item);
} finally {
sqlSession.close();
}
}
上面这段代码先创建一个SqlSessionFactory，然后通过SqlSessionFactory获取一个SqlSession，然后在从SqlSession获取需要的mapper。
而我们在实际项目中都是通过spring来使用mybatis，如下配置：
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.letv.shop.web.dao" />
<property name="sqlSessionFactoryBeanName" value="couponSessionFactory" />
</bean>
<bean id="couponSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource"></property>
<property name="mapperLocations" value="classpath:mybatis/*.xml"></property>
<property name="typeAliasesPackage" value="com.letv.shop.domain"/>
</bean>
@Override
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
for (BeanDefinitionHolder holder : beanDefinitions) {//获取所有路径下的mapper接口
GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition();
//设置Bean的真实类型MapperFactoryBean
definition.setBeanClass(MapperFactoryBean.class);
}
//这个集合返回以后 Spring容器会将里面的所有内容注册到容器中
return beanDefinitions;
}
项目启动阶段会扫描配置路径下所有mapper接口，然后将其beanClass都设置为MapperFactoryBean，并且注册到spring容器中。
然后通过spring容器获取mapper的时候，获取的bean的beanClass是MapperFactoryBean，bean实例调用的是MapperFactoryBean的getObject方法：
public T getObject() throws Exception {
return this.getSqlSession().getMapper(this.mapperInterface);
}
可以发现，不论哪种方式，最终都是获取一个SqlSession，从SqlSession中获取mapper。
接下来我们以第一种方法为入口开始分析。
public static void main(String[] args) throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
//入口
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
Employee employeeMapper = sqlSession.getMapper(Employee.class);
List<Employee> all = employeeMapper.getAll();
for (Employee item : all)
System.out.println(item);
} finally {
sqlSession.close();
}
}
首先看下SqlSessionFactory是如何生成的？
// SqlSessionFactoryBuilder
public SqlSessionFactory build(InputStream inputStream) {
return this.build((InputStream)inputStream, (String)null, (Properties)null);
}
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
// 创建配置文件解析器
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
//解析配置文件，生成Configuration对象
//入口1
Configuration configuration = parser.parse();
//通过Configuration对象生成SqlSessionFactory
//入口2
SqlSessionFactory var5 = this.build(configuration);
return var5;
}
其实就是将配置文件的内容解析出来封装到Configuration中。所以先来认识一下xml配置文件和Configuration类。
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!-- 全局配置顶级节点 -->
<configuration>
<!-- 属性配置,读取properties中的配置文件 -->
<properties resource="db.propertis">
<property name="XXX" value="XXX"/>
</properties>
<!-- 类型别名 -->
<typeAliases>
<!-- 在用到User类型的时候,可以直接使用别名,不需要输入User类的全部路径 -->
<typeAlias type="com.luck.codehelp.entity.User" alias="user"/>
</typeAliases>
<!-- 类型处理器 -->
<typeHandlers>
<!-- 类型处理器的作用是完成JDBC类型和java类型的转换,mybatis默认已经由了很多类型处理器,正常无需自定义-->
</typeHandlers>
<!-- 对象工厂 -->
<!-- mybatis创建结果对象的新实例时,会通过对象工厂来完成，mybatis有默认的对象工厂，正常无需配置 -->
<objectFactory type=""></objectFactory>
<!-- 插件 -->
<plugins>
<!-- 可以自定义拦截器通过plugin标签加入 -->
<plugin interceptor="com.lucky.interceptor.MyPlugin"></plugin>
</plugins>
<!-- 全局配置参数 -->
<settings>
<setting name="cacheEnabled" value="false" />
<setting name="useGeneratedKeys" value="true" /><!-- 是否自动生成主键 -->
<setting name="defaultExecutorType" value="REUSE" />
<setting name="lazyLoadingEnabled" value="true"/><!-- 延迟加载标识 -->
<setting name="aggressiveLazyLoading" value="true"/><!--有延迟加载属性的对象是否延迟加载 -->
<setting name="multipleResultSetsEnabled" value="true"/><!-- 是否允许单个语句返回多个结果集 -->
<setting name="useColumnLabel" value="true"/><!-- 使用列标签而不是列名 -->
<setting name="autoMappingBehavior" value="PARTIAL"/><!-- 指定mybatis如何自动映射列到字段属性;NONE:自动映射;PARTIAL:只会映射结果没有嵌套的结果;FULL:可以映射任何复杂的结果 -->
<setting name="defaultExecutorType" value="SIMPLE"/><!-- 默认执行器类型 -->
<setting name="defaultFetchSize" value=""/>
<setting name="defaultStatementTimeout" value="5"/><!-- 驱动等待数据库相应的超时时间 ,单位是秒-->
<setting name="safeRowBoundsEnabled" value="false"/><!-- 是否允许使用嵌套语句RowBounds -->
<setting name="safeResultHandlerEnabled" value="true"/>
<setting name="mapUnderscoreToCamelCase" value="false"/><!-- 下划线列名是否自动映射到驼峰属性：如user_id映射到userId -->
<setting name="localCacheScope" value="SESSION"/><!-- 本地缓存（session是会话级别） -->
<setting name="jdbcTypeForNull" value="OTHER"/><!-- 数据为空值时,没有特定的JDBC类型的参数的JDBC类型 -->
<setting name="lazyLoadTriggerMethods" value="equals,clone,hashCode,toString"/><!-- 指定触发延迟加载的对象的方法 -->
<setting name="callSettersOnNulls" value="false"/><!--如果setter方法或map的put方法，如果检索到的值为null时，数据是否有用 -->
<setting name="logPrefix" value="XXXX"/><!-- mybatis日志文件前缀字符串 -->
<setting name="logImpl" value="SLF4J"/><!-- mybatis日志的实现类 -->
<setting name="proxyFactory" value="CGLIB"/><!-- mybatis代理工具 -->
</settings>
<!-- 环境配置集合 -->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/><!-- 事务管理器 -->
<dataSource type="POOLED"><!-- 数据库连接池 -->
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
<!-- mapper文件映射配置 -->
<mappers>
<mapper resource="com/luck/codehelp/mapper/UserMapper.xml"/>
</mappers>
</configuration>
Configuration属性：
public class Configuration {
protected Environment environment;//运行环境
protected boolean safeRowBoundsEnabled = false;
protected boolean safeResultHandlerEnabled = true;
protected boolean mapUnderscoreToCamelCase = false;
protected boolean aggressiveLazyLoading = true; //true：有延迟加载属性的对象被调用时完全加载任意属性;false：每个属性按需要加载
protected boolean multipleResultSetsEnabled = true;//是否允许多种结果集从一个单独的语句中返回
protected boolean useGeneratedKeys = false;//是否支持自动生成主键
protected boolean useColumnLabel = true;//是否使用列标签
protected boolean cacheEnabled = true;//是否使用缓存标识
protected boolean callSettersOnNulls = false;//
protected boolean useActualParamName = true;
protected String logPrefix;
protected Class <? extends Log> logImpl;
protected Class <? extends VFS> vfsImpl;
protected LocalCacheScope localCacheScope = LocalCacheScope.SESSION;
protected JdbcType jdbcTypeForNull = JdbcType.OTHER;
protected Set<String> lazyLoadTriggerMethods = new HashSet<String>(Arrays.asList(new String[] { "equals", "clone", "hashCode", "toString" }));
protected Integer defaultStatementTimeout;
protected Integer defaultFetchSize;
protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
protected AutoMappingBehavior autoMappingBehavior = AutoMappingBehavior.PARTIAL;//指定mybatis如果自动映射列到字段和属性,PARTIAL会自动映射简单的没有嵌套的结果,FULL会自动映射任意复杂的结果
protected AutoMappingUnknownColumnBehavior autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
protected Properties variables = new Properties();
protected ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
protected ObjectFactory objectFactory = new DefaultObjectFactory();
protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
protected boolean lazyLoadingEnabled = false;//是否延时加载，false则表示所有关联对象即使加载,true表示延时加载
protected ProxyFactory proxyFactory = new JavassistProxyFactory(); // #224 Using internal Javassist instead of OGNL
protected String databaseId;
protected Class<?> configurationFactory;
protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
protected final InterceptorChain interceptorChain = new InterceptorChain();
protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry();
protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();
protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>("Mapped Statements collection");
protected final Map<String, Cache> caches = new StrictMap<Cache>("Caches collection");
protected final Map<String, ResultMap> resultMaps = new StrictMap<ResultMap>("Result Maps collection");
protected final Map<String, ParameterMap> parameterMaps = new StrictMap<ParameterMap>("Parameter Maps collection");
protected final Map<String, KeyGenerator> keyGenerators = new StrictMap<KeyGenerator>("Key Generators collection");
protected final Set<String> loadedResources = new HashSet<String>(); //已经加载过的resource(mapper)
protected final Map<String, XNode> sqlFragments = new StrictMap<XNode>("XML fragments parsed from previous mappers");
protected final Collection<XMLStatementBuilder> incompleteStatements = new LinkedList<XMLStatementBuilder>();
protected final Collection<CacheRefResolver> incompleteCacheRefs = new LinkedList<CacheRefResolver>();
protected final Collection<ResultMapResolver> incompleteResultMaps = new LinkedList<ResultMapResolver>();
protected final Collection<MethodResolver> incompleteMethods = new LinkedList<MethodResolver>();
protected final Map<String, String> cacheRefMap = new HashMap<String, String>();
}
Configuration构造器：注意，这里创建了一个用来存放mapper别名的typeAliasRegistry ，并且初始化好多mapper进去。
public Configuration() {
this.safeRowBoundsEnabled = false;
this.safeResultHandlerEnabled = true;
this.mapUnderscoreToCamelCase = false;
this.aggressiveLazyLoading = true;
this.multipleResultSetsEnabled = true;
this.useGeneratedKeys = false;
this.useColumnLabel = true;
this.cacheEnabled = true;
this.callSettersOnNulls = false;
this.localCacheScope = LocalCacheScope.SESSION;
this.jdbcTypeForNull = JdbcType.OTHER;
this.lazyLoadTriggerMethods = new HashSet(Arrays.asList("equals", "clone", "hashCode", "toString"));
this.defaultExecutorType = ExecutorType.SIMPLE;
this.autoMappingBehavior = AutoMappingBehavior.PARTIAL;
this.autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
this.variables = new Properties();
this.reflectorFactory = new DefaultReflectorFactory();
this.objectFactory = new DefaultObjectFactory();
this.objectWrapperFactory = new DefaultObjectWrapperFactory();
this.mapperRegistry = new MapperRegistry(this);
this.lazyLoadingEnabled = false;
this.proxyFactory = new JavassistProxyFactory();
this.interceptorChain = new InterceptorChain();
this.typeHandlerRegistry = new TypeHandlerRegistry();
//这个属性就是用来存储mapper的
this.typeAliasRegistry = new TypeAliasRegistry();
this.languageRegistry = new LanguageDriverRegistry();
this.mappedStatements = new Configuration.StrictMap("Mapped Statements collection");
this.caches = new Configuration.StrictMap("Caches collection");
this.resultMaps = new Configuration.StrictMap("Result Maps collection");
this.parameterMaps = new Configuration.StrictMap("Parameter Maps collection");
this.keyGenerators = new Configuration.StrictMap("Key Generators collection");
this.loadedResources = new HashSet();
this.sqlFragments = new Configuration.StrictMap("XML fragments parsed from previous mappers");
this.incompleteStatements = new LinkedList();
this.incompleteCacheRefs = new LinkedList();
this.incompleteResultMaps = new LinkedList();
this.incompleteMethods = new LinkedList();
this.cacheRefMap = new HashMap();
//这里初始化了好多mapper
this.typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
this.typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
this.typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
this.typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
this.typeAliasRegistry.registerAlias("LRU", LruCache.class);
this.typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
this.typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
this.typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
this.typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
this.typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
this.typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
this.typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
this.typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
this.typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
this.typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
this.typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
this.typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
this.typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
this.typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
this.languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
this.languageRegistry.register(RawLanguageDriver.class);
}
TypeAliasRegistry：内部是一个map
public class TypeAliasRegistry {
//内部是一个map
private final Map<String, Class<?>> TYPE_ALIASES = new HashMap();
public TypeAliasRegistry() {
this.registerAlias("string", String.class);
this.registerAlias("byte", Byte.class);
this.registerAlias("long", Long.class);
this.registerAlias("short", Short.class);
this.registerAlias("int", Integer.class);
this.registerAlias("integer", Integer.class);
this.registerAlias("double", Double.class);
this.registerAlias("float", Float.class);
this.registerAlias("boolean", Boolean.class);
this.registerAlias("byte[]", Byte[].class);
this.registerAlias("long[]", Long[].class);
this.registerAlias("short[]", Short[].class);
this.registerAlias("int[]", Integer[].class);
this.registerAlias("integer[]", Integer[].class);
this.registerAlias("double[]", Double[].class);
this.registerAlias("float[]", Float[].class);
this.registerAlias("boolean[]", Boolean[].class);
this.registerAlias("_byte", Byte.TYPE);
this.registerAlias("_long", Long.TYPE);
this.registerAlias("_short", Short.TYPE);
this.registerAlias("_int", Integer.TYPE);
this.registerAlias("_integer", Integer.TYPE);
this.registerAlias("_double", Double.TYPE);
this.registerAlias("_float", Float.TYPE);
this.registerAlias("_boolean", Boolean.TYPE);
this.registerAlias("_byte[]", byte[].class);
this.registerAlias("_long[]", long[].class);
this.registerAlias("_short[]", short[].class);
this.registerAlias("_int[]", int[].class);
this.registerAlias("_integer[]", int[].class);
this.registerAlias("_double[]", double[].class);
this.registerAlias("_float[]", float[].class);
this.registerAlias("_boolean[]", boolean[].class);
this.registerAlias("date", Date.class);
this.registerAlias("decimal", BigDecimal.class);
this.registerAlias("bigdecimal", BigDecimal.class);
this.registerAlias("biginteger", BigInteger.class);
this.registerAlias("object", Object.class);
this.registerAlias("date[]", Date[].class);
this.registerAlias("decimal[]", BigDecimal[].class);
this.registerAlias("bigdecimal[]", BigDecimal[].class);
this.registerAlias("biginteger[]", BigInteger[].class);
this.registerAlias("object[]", Object[].class);
this.registerAlias("map", Map.class);
this.registerAlias("hashmap", HashMap.class);
this.registerAlias("list", List.class);
this.registerAlias("arraylist", ArrayList.class);
this.registerAlias("collection", Collection.class);
this.registerAlias("iterator", Iterator.class);
this.registerAlias("ResultSet", ResultSet.class);
}
}
接下来看看具体是如何解析xml的：
//XMLConfigBuilder
public Configuration parse() {
if (this.parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
} else {
this.parsed = true;
//入口
this.parseConfiguration(this.parser.evalNode("/configuration"));
return this.configuration;
}
}
// XMLConfigBuilder
private void parseConfiguration(XNode root) {
try {
private void parseConfiguration(XNode root) {
try {
// 解析 properties 配置
propertiesElement(root.evalNode("properties"));
// 解析 settings 配置，并将其转换为 Properties 对象
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
// settings 中的信息设置到 Configuration 对象中
settingsElement(settings);
// 解析 typeAliases 配置
typeAliasesElement(root.evalNode("typeAliases"));
// 解析 plugins 配置
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
// 解析 environments 配置
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
// 解析 mappers 配置
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
解析 properties 配置
<properties resource="db.properties">
<property name="username" value="root"/>
<property name="password" value="123456"/>
</properties>
//XMLConfigBuilder
private void propertiesElement(XNode context) throws Exception {
if (context != null) {
// 解析 propertis 的子节点，并将这些节点内容转换为属性对象 Properties
//入口
Properties defaults = context.getChildrenAsProperties();
// 获取 propertis 节点中的 resource 和 url 属性值
String resource = context.getStringAttribute("resource");
String url = context.getStringAttribute("url");
// 两者都不为空，则抛出异常
if (resource != null && url != null) {
throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference. Please specify one or the other.");
}
if (resource != null) {
// 从文件系统中加载并解析属性文件
defaults.putAll(Resources.getResourceAsProperties(resource));
} else if (url != null) {
// 通过 url 加载并解析属性文件
defaults.putAll(Resources.getUrlAsProperties(url));
}
Properties vars = configuration.getVariables();
if (vars != null) {
defaults.putAll(vars);
}
parser.setVariables(defaults);
// 将属性值设置到 configuration 中
configuration.setVariables(defaults);
}
}
public Properties getChildrenAsProperties() {
//创建一个Properties对象
Properties properties = new Properties();
// 获取并遍历子节点
for (XNode child : getChildren()) {
// 获取 property 节点的 name 和 value 属性
String name = child.getStringAttribute("name");
String value = child.getStringAttribute("value");
if (name != null && value != null) {
// 设置属性到属性对象中
properties.setProperty(name, value);
}
}
return properties;
}
需要注意的是，propertiesElement 方法是先解析 properties 节点的子节点内容，后再从文件系统或者网络读取属性配置，并将所有的属性及属性值都放入到 defaults 属性对象中。这就会存在同名属性覆盖的问题，也就是从文件系统，或者网络上读取到的属性及属性值会覆盖掉 properties 子节点中同名的属性和及值。
解析 settings 配置
<settings>
<setting name="cacheEnabled" value="true"/>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="autoMappingBehavior" value="PARTIAL"/>
</settings>
// XMLConfigBuilder
private Properties settingsAsProperties(XNode context) {
if (context == null) {
return new Properties();
}
// 获取 settings 子节点中的内容，解析成Properties，getChildrenAsProperties 方法前面已分析过
Properties props = context.getChildrenAsProperties();
// 创建 Configuration 类的“元信息”对象
MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);
for (Object key : props.keySet()) {
// 检测 Configuration 中是否存在相关属性，不存在则抛出异常
if (!metaConfig.hasSetter(String.valueOf(key))) {
throw new BuilderException("The setting " + key + " is not known. Make sure you spelled it correctly (case sensitive).");
}
}
return props;
}
设置 settings 配置到 Configuration 中
// XMLConfigBuilder
private void settingsElement(Properties props) throws Exception {
// 设置 autoMappingBehavior 属性，默认值为 PARTIAL
configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));
// 设置 cacheEnabled 属性，默认值为 true
configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));
// 解析默认的枚举处理器
Class<? extends TypeHandler> typeHandler = (Class<? extends TypeHandler>)resolveClass(props.getProperty("defaultEnumTypeHandler"));
// 设置默认枚举处理器
configuration.setDefaultEnumTypeHandler(typeHandler);
configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
configuration.setUseActualParamName(booleanValueOf(props.getProperty("useActualParamName"), true));
}
解析 typeAliases 配置
在 MyBatis 中，可以为我们自己写的有些类定义一个别名。这样在使用的时候，我们只需要输入别名即可，无需再把全限定的类名写出来。在 MyBatis 中，我们有两种方式进行别名配置。第一种是仅配置包名，让 MyBatis 去扫描包中的类型，并根据类型得到相应的别名
<typeAliases>
<package name="com.mybatis.model"/>
</typeAliases>
第二种方式是通过手动的方式，明确为某个类型配置别名。这种方式的配置如下：
<typeAliases>
<typeAlias alias="employe" type="com.mybatis.model.Employe" />
<typeAlias type="com.mybatis.model.User" />//alias不是必须的，没配置的话就是user
</typeAliases>
// XMLConfigBuilder
private void typeAliasesElement(XNode parent) {
if (parent != null) {
for (XNode child : parent.getChildren()) {
// 第一种方式：自动扫描
if ("package".equals(child.getName())) {
String typeAliasPackage = child.getStringAttribute("name");
//入口3
configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
} else {//第二种方式：配置别名
// 获取 alias 和 type 属性值，alias 不是必填项，可为空
String alias = child.getStringAttribute("alias");
String type = child.getStringAttribute("type");
try {
// 加载 type 对应的类型
Class<?> clazz = Resources.classForName(type);
// 注册别名到类型的映射
if (alias == null) {
//入口1
typeAliasRegistry.registerAlias(clazz);
} else {
//入口2
typeAliasRegistry.registerAlias(alias, clazz);
}
} catch (ClassNotFoundException e) {
throw new BuilderException("Error registering typeAlias for ‘" + alias + "‘. Cause: " + e, e);
}
}
}
}
}
注册的alias分三种情况：1、指定package 2、指定class 3、指定class和type
先看后两个：
//TypeAliasRegistry
private final Map<String, Class<?>> TYPE_ALIASES = new HashMap<String, Class<?>>();
public void registerAlias(Class<?> type) {
// 获取全路径类名的简称
String alias = type.getSimpleName();
Alias aliasAnnotation = type.getAnnotation(Alias.class);
if (aliasAnnotation != null) {
// 从注解中取出别名
alias = aliasAnnotation.value();
}
// 调用重载方法注册别名和类型映射
registerAlias(alias, type);
}
public void registerAlias(String alias, Class<?> value) {
if (alias == null) {
throw new TypeException("The parameter alias cannot be null");
}
// 将别名转成小写
String key = alias.toLowerCase(Locale.ENGLISH);
/*
* 如果 TYPE_ALIASES 中存在了某个类型映射，这里判断当前类型与映射中的类型是否一致，
* 不一致则抛出异常，不允许一个别名对应两种类型
*/
if (TYPE_ALIASES.containsKey(key) && TYPE_ALIASES.get(key) != null && !TYPE_ALIASES.get(key).equals(value)) {
throw new TypeException(
"The alias ‘" + alias + "‘ is already mapped to the value ‘" + TYPE_ALIASES.get(key).getName() + "‘.");
}
// 缓存别名到类型映射
TYPE_ALIASES.put(key, value);
}
在看第一个：
public void registerAliases(String packageName) {
registerAliases(packageName, Object.class);
}
public void registerAliases(String packageName, Class<?> superType) {
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
Set<Class<? extends Class<?>>> typeSet = resolverUtil.getClasses();
//查找指定包下的所有类，遍历查找到的类型集合，为每个类型注册别名
for (Class<?> type : typeSet) {
// 忽略匿名类，接口，内部类
if (!type.isAnonymousClass() && !type.isInterface() && !type.isMemberClass()) {
// 为类型注册别名
registerAlias(type);
}
}
}
解析 plugins 配置
插件是 MyBatis 提供的一个拓展机制，通过插件机制我们可在 SQL 执行过程中的某些点上做一些自定义操作。比喻分页插件，在SQL执行之前动态拼接语句，我们后面会单独来讲插件机制，先来了解插件的配置。如下：
<plugins>
<plugin interceptor="com.github.pagehelper.PageInterceptor">
<property name="helperDialect" value="mysql"/>
</plugin>
</plugins>
// XMLConfigBuilder
private void pluginElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
String interceptor = child.getStringAttribute("interceptor");
// 获取配置信息
Properties properties = child.getChildrenAsProperties();
// 解析拦截器的类型，并创建拦截器
Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
// 设置属性
interceptorInstance.setProperties(properties);
// 添加拦截器到 Configuration 中
configuration.addInterceptor(interceptorInstance);
}
}
}
// Configuration
public void addInterceptor(Interceptor interceptor) {
this.interceptorChain.addInterceptor(interceptor);
}
就是解析出plugin，创建一个拦截器，然后放入到interceptorChain中，看一下interceptorChain长啥样。
public class InterceptorChain {
//一个拦截器集合
private final List<Interceptor> interceptors = new ArrayList();
}
解析 environments 配置
在 MyBatis 中，事务管理器和数据源是配置在 environments 中的。
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
// XMLConfigBuilder
private void environmentsElement(XNode context) throws Exception {
if (context != null) {
if (environment == null) {
// 获取 default 属性
environment = context.getStringAttribute("default");
}
for (XNode child : context.getChildren()) {
// 获取 id 属性
String id = child.getStringAttribute("id");
/*
* 检测当前 environment 节点的 id 与其父节点 environments 的属性 default
* 内容是否一致，一致则返回 true，否则返回 false
* 将其default属性值与子元素environment的id属性值相等的子元素设置为当前使用的Environment对象
*/
if (isSpecifiedEnvironment(id)) {
// 将environment中的transactionManager标签转换为TransactionFactory对象
//入口1
TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
// 将environment中的dataSource标签转换为DataSourceFactory对象
//入口2
DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
// 创建 DataSource 对象
DataSource dataSource = dsFactory.getDataSource();
Environment.Builder environmentBuilder = new Environment.Builder(id)
.transactionFactory(txFactory)
.dataSource(dataSource);
// 构建 Environment 对象，并设置到 configuration 中
configuration.setEnvironment(environmentBuilder.build());
}
}
}
}
private TransactionFactory transactionManagerElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
Properties props = context.getChildrenAsProperties();
//通过别名获取Class,并实例化
TransactionFactory factory = (TransactionFactory)this.resolveClass(type).newInstance();
factory.setProperties(props);
return factory;
} else {
throw new BuilderException("Environment declaration requires a TransactionFactory.");
}
}
private DataSourceFactory dataSourceElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
//通过别名获取Class,并实例化
Properties props = context.getChildrenAsProperties();
DataSourceFactory factory = (DataSourceFactory)this.resolveClass(type).newInstance();
factory.setProperties(props);
return factory;
} else {
throw new BuilderException("Environment declaration requires a DataSourceFactory.");
}
}
中type有"JDBC"、"MANAGED"这两种配置，而我们前面Configuration中默认注册的别名中有对应的JdbcTransactionFactory.class、ManagedTransactionFactory.class这两个TransactionFactory
中type有"JNDI"、"POOLED"、"UNPOOLED"这三种配置，默认注册的别名中有对应的JndiDataSourceFactory.class、PooledDataSourceFactory.class、UnpooledDataSourceFactory.class这三个DataSourceFactory
而我们的environment配置中transactionManager type="JDBC"和dataSource type="POOLED"，则生成的transactionManager为JdbcTransactionFactory，DataSourceFactory为PooledDataSourceFactory
解析 mappers 配置
mapperElement方法会将mapper标签内的元素转换成MapperProxyFactory产生的代理类，和与mapper.xml文件的绑定，这里先预留个位置，后面要详细讲解。
到现在所有标签解析完毕，并且都封装到Configuration中了，最后一步就是将Configuration在封装到SqlSessionFactory中。
//只是将configuration设置为其属性
public DefaultSqlSessionFactory(Configuration configuration) {
this.configuration = configuration;
}
原文地址：https://www.cnblogs.com/yanhui007/p/12601023.html
时间： 2024-10-12 14:23:36