Mybaits 源码解析 (二)----- 根据配置文件创建…
2019-10-28 06:33:18来源:博客园 阅读 ()
Mybaits 源码解析 (二)----- 根据配置文件创建SqlSessionFactory(Configuration的创建过程)
我们使用mybatis操作数据库都是通过SqlSession的API调用,而创建SqlSession是通过SqlSessionFactory。下面我们就看看SqlSessionFactory的创建过程。
配置文件解析入口
我们看看第一篇文章中的测试方法
1 public static void main(String[] args) throws IOException { 2 String resource = "mybatis-config.xml"; 3 InputStream inputStream = Resources.getResourceAsStream(resource); 4 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 5 SqlSession sqlSession = sqlSessionFactory.openSession(); 6 try { 7 Employee employeeMapper = sqlSession.getMapper(Employee.class); 8 List<Employee> all = employeeMapper.getAll(); 9 for (Employee item : all) 10 System.out.println(item); 11 } finally { 12 sqlSession.close(); 13 } 14 }
首先,我们使用 MyBatis 提供的工具类 Resources 加载配置文件,得到一个输入流。然后再通过 SqlSessionFactoryBuilder 对象的build
方法构建 SqlSessionFactory 对象。所以这里的 build 方法是我们分析配置文件解析过程的入口方法。我们看看build里面是代码:
public SqlSessionFactory build(InputStream inputStream) { // 调用重载方法 return build(inputStream, null, null); } public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { try { // 创建配置文件解析器 XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties); // 调用 parser.parse() 方法解析配置文件,生成 Configuration 对象 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) { // 创建 DefaultSqlSessionFactory,将解析配置文件后生成的Configuration传入 return new DefaultSqlSessionFactory(config); }
SqlSessionFactory是通过SqlSessionFactoryBuilder的build方法创建的,build方法内部是通过一个XMLConfigBuilder对象解析mybatis-config.xml文件生成一个Configuration对象。XMLConfigBuilder从名字可以看出是解析Mybatis配置文件的,其实它是继承了一个父类BaseBuilder,其每一个子类多是以XMLXXXXXBuilder命名的,也就是其子类都对应解析一种xml文件或xml文件中一种元素。
我们看看XMLConfigBuilder的构造方法:
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; }
可以看到调用了父类的构造方法,并传入一个new Configuration()对象,这个对象也就是最终的Mybatis配置对象
我们先来看看其基类BaseBuilder
public abstract class BaseBuilder { protected final Configuration configuration; protected final TypeAliasRegistry typeAliasRegistry; protected final TypeHandlerRegistry typeHandlerRegistry; public BaseBuilder(Configuration configuration) { this.configuration = configuration; this.typeAliasRegistry = this.configuration.getTypeAliasRegistry(); this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry(); } .... }
BaseBuilder中只有三个成员变量,而typeAliasRegistry和typeHandlerRegistry都是直接从Configuration的成员变量获得的,接着我们看看Configuration这个类
Configuration类位于mybatis包的org.apache.ibatis.session目录下,其属性就是对应于mybatis的全局配置文件mybatis-config.xml的配置,将XML配置中的内容解析赋值到Configuration对象中。
由于XML配置项有很多,所以Configuration类的属性也很多。先来看下Configuration对于的XML配置文件示例:
<?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>
而对于XML的配置,Configuration类的属性是和XML配置对应的。Configuration类属性如下:
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>(); //其他方法略 }
加载的过程是SqlSessionFactoryBuilder根据xml配置的文件流,通过XMLConfigBuilder的parse方法进行解析得到一个Configuration对象,我们再看看其构造函数
1 public Configuration() { 2 this.safeRowBoundsEnabled = false; 3 this.safeResultHandlerEnabled = true; 4 this.mapUnderscoreToCamelCase = false; 5 this.aggressiveLazyLoading = true; 6 this.multipleResultSetsEnabled = true; 7 this.useGeneratedKeys = false; 8 this.useColumnLabel = true; 9 this.cacheEnabled = true; 10 this.callSettersOnNulls = false; 11 this.localCacheScope = LocalCacheScope.SESSION; 12 this.jdbcTypeForNull = JdbcType.OTHER; 13 this.lazyLoadTriggerMethods = new HashSet(Arrays.asList("equals", "clone", "hashCode", "toString")); 14 this.defaultExecutorType = ExecutorType.SIMPLE; 15 this.autoMappingBehavior = AutoMappingBehavior.PARTIAL; 16 this.autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE; 17 this.variables = new Properties(); 18 this.reflectorFactory = new DefaultReflectorFactory(); 19 this.objectFactory = new DefaultObjectFactory(); 20 this.objectWrapperFactory = new DefaultObjectWrapperFactory(); 21 this.mapperRegistry = new MapperRegistry(this); 22 this.lazyLoadingEnabled = false; 23 this.proxyFactory = new JavassistProxyFactory(); 24 this.interceptorChain = new InterceptorChain(); 25 this.typeHandlerRegistry = new TypeHandlerRegistry(); 26 this.typeAliasRegistry = new TypeAliasRegistry(); 27 this.languageRegistry = new LanguageDriverRegistry(); 28 this.mappedStatements = new Configuration.StrictMap("Mapped Statements collection"); 29 this.caches = new Configuration.StrictMap("Caches collection"); 30 this.resultMaps = new Configuration.StrictMap("Result Maps collection"); 31 this.parameterMaps = new Configuration.StrictMap("Parameter Maps collection"); 32 this.keyGenerators = new Configuration.StrictMap("Key Generators collection"); 33 this.loadedResources = new HashSet(); 34 this.sqlFragments = new Configuration.StrictMap("XML fragments parsed from previous mappers"); 35 this.incompleteStatements = new LinkedList(); 36 this.incompleteCacheRefs = new LinkedList(); 37 this.incompleteResultMaps = new LinkedList(); 38 this.incompleteMethods = new LinkedList(); 39 this.cacheRefMap = new HashMap(); 40 this.typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class); 41 this.typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class); 42 this.typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class); 43 this.typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class); 44 this.typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class); 45 this.typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class); 46 this.typeAliasRegistry.registerAlias("FIFO", FifoCache.class); 47 this.typeAliasRegistry.registerAlias("LRU", LruCache.class); 48 this.typeAliasRegistry.registerAlias("SOFT", SoftCache.class); 49 this.typeAliasRegistry.registerAlias("WEAK", WeakCache.class); 50 this.typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class); 51 this.typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class); 52 this.typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class); 53 this.typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class); 54 this.typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class); 55 this.typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class); 56 this.typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class); 57 this.typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class); 58 this.typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class); 59 this.typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class); 60 this.typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class); 61 this.typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class); 62 this.languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class); 63 this.languageRegistry.register(RawLanguageDriver.class); 64 }
我们看到第26行this.typeAliasRegistry = new TypeAliasRegistry();,并且第40到61行向 typeAliasRegistry 注册了很多别名,我们看看TypeAliasRegistry
public class TypeAliasRegistry { 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); } public void registerAliases(String packageName) { this.registerAliases(packageName, Object.class); } //略 }
其实TypeAliasRegistry里面有一个HashMap,并且在TypeAliasRegistry的构造器中注册很多别名到这个hashMap中,好了,到现在我们只是创建了一个 XMLConfigBuilder,在其构造器中我们创建了一个 Configuration 对象,接下来我们看看将mybatis-config.xml解析成Configuration中对应的属性,也就是parser.parse()方法:
XMLConfigBuilder
1 public Configuration parse() { 2 if (parsed) { 3 throw new BuilderException("Each XMLConfigBuilder can only be used once."); 4 } 5 parsed = true; 6 // 解析配置 7 parseConfiguration(parser.evalNode("/configuration")); 8 return configuration; 9 }
我们看看第7行,注意一个 xpath 表达式 - /configuration
。这个表达式代表的是 MyBatis 的<configuration/>
标签,这里选中这个标签,并传递给parseConfiguration
方法。我们继续跟下去。
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")); // 加载 vfs loadCustomVfs(settings); // 解析 typeAliases 配置 typeAliasesElement(root.evalNode("typeAliases")); // 解析 plugins 配置 pluginElement(root.evalNode("plugins")); // 解析 objectFactory 配置 objectFactoryElement(root.evalNode("objectFactory")); // 解析 objectWrapperFactory 配置 objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); // 解析 reflectorFactory 配置 reflectorFactoryElement(root.evalNode("reflectorFactory")); // settings 中的信息设置到 Configuration 对象中 settingsElement(settings); // 解析 environments 配置 environmentsElement(root.evalNode("environments")); // 解析 databaseIdProvider,获取并设置 databaseId 到 Configuration 对象 databaseIdProviderElement(root.evalNode("databaseIdProvider")); // 解析 typeHandlers 配置 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); } }
解析 properties 配置
先来看一下 properties 节点的配置内容。如下:
<properties resource="db.properties"> <property name="username" value="root"/> <property name="password" value="123456"/> </properties>
我为 properties 节点配置了一个 resource 属性,以及两个子节点。接着我们看看propertiesElement的逻辑
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 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"); // 两者都不用空,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; } // -☆- XNode public List<XNode> getChildren() { List<XNode> children = new ArrayList<XNode>(); // 获取子节点列表 NodeList nodeList = node.getChildNodes(); if (nodeList != null) { for (int i = 0, n = nodeList.getLength(); i < n; i++) { Node node = nodeList.item(i); if (node.getNodeType() == Node.ELEMENT_NODE) { children.add(new XNode(xpathParser, node, variables)); } } } return children; }
解析properties主要分三个步骤:
- 解析 properties 节点的子节点,并将解析结果设置到 Properties 对象中。
- 从文件系统或通过网络读取属性配置,这取决于 properties 节点的 resource 和 url 是否为空。
- 将解析出的属性对象设置到 XPathParser 和 Configuration 对象中。
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 节点的解析过程
下面先来看一个settings比较简单的配置,如下:
<settings> <setting name="cacheEnabled" value="true"/> <setting name="lazyLoadingEnabled" value="true"/> <setting name="autoMappingBehavior" value="PARTIAL"/> </settings>
接着来看看settingsAsProperties
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
接着我们看看将 settings 配置设置到 Configuration 对象中的过程。如下:
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)); // 省略部分代码 // 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)); // 省略部分代码 }
上面代码处理调用 Configuration 的 setter 方法
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" /> </typeAliases>
下面我们来看一下两种不同的别名配置是怎样解析的。代码如下:
XMLConfigBuilder
private void typeAliasesElement(XNode parent) { if (parent != null) { for (XNode child : parent.getChildren()) { // 从指定的包中解析别名和类型的映射 if ("package".equals(child.getName())) { String typeAliasPackage = child.getStringAttribute("name"); configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage); // 从 typeAlias 节点中解析别名和类型的映射 } else { // 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) { typeAliasRegistry.registerAlias(clazz); } else { typeAliasRegistry.registerAlias(alias, clazz); } } catch (ClassNotFoundException e) { throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e); } } } } }
我们看到通过包扫描和手动注册时通过子节点名称是否package来判断的
从 typeAlias 节点中解析并注册别名
在别名的配置中,type
属性是必须要配置的,而alias
属性则不是必须的。
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); }
若用户为明确配置 alias 属性,MyBatis 会使用类名的小写形式作为别名。比如,全限定类名com.mybatis.model.User的别名为user。若类中有@Alias注解,则从注解中取值作为别名。
从指定的包中解析并注册别名
public void registerAliases(String packageName) { registerAliases(packageName, Object.class); } public void registerAliases(String packageName, Class<?> superType) { ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>(); /* * 查找包下的父类为 Object.class 的类。 * 查找完成后,查找结果将会被缓存到resolverUtil的内部集合中。 */ resolverUtil.find(new ResolverUtil.IsA(superType), packageName); // 获取查找结果 Set<Class<? extends Class<?>>> typeSet = resolverUtil.getClasses(); 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); } } }
主要分为两个步骤:
- 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
我们看看查找指定包下的所有类
private Set<Class<? extends T>> matches = new HashSet(); public ResolverUtil<T> find(ResolverUtil.Test test, String packageName) { //将包名转换成文件路径 String path = this.getPackagePath(packageName); try { //通过 VFS(虚拟文件系统)获取指定包下的所有文件的路径名,比如com/mybatis/model/Employe.class List<String> children = VFS.getInstance().list(path); Iterator i$ = children.iterator(); while(i$.hasNext()) { String child = (String)i$.next(); //以.class结尾的文件就加入到Set集合中 if (child.endsWith(".class")) { this.addIfMatching(test, child); } } } catch (IOException var7) { log.error("Could not read package: " + packageName, var7); } return this; } protected String getPackagePath(String packageName) { //将包名转换成文件路径 return packageName == null ? null : packageName.replace('.', '/'); } protected void addIfMatching(ResolverUtil.Test test, String fqn) { try { //将路径名转成全限定的类名,通过类加载器加载类名,比如com.mybatis.model.Employe.class String externalName = fqn.substring(0, fqn.indexOf(46)).replace('/', '.'); ClassLoader loader = this.getClassLoader(); if (log.isDebugEnabled()) { log.debug("Checking to see if class " + externalName + " matches criteria [" + test + "]"); } Class<?> type = loader.loadClass(externalName); if (test.matches(type)) { //加入到matches集合中 this.matches.add(type); } } catch (Throwable var6) { log.warn("Could not examine class '" + fqn + "'" + " due to a " + var6.getClass().getName() + " with message: " + var6.getMessage()); } }
主要有以下几步:
- 通过 VFS(虚拟文件系统)获取指定包下的所有文件的路径名,比如 com/mybatis/model/Employe.class
- 筛选以
.class
结尾的文件名 - 将路径名转成全限定的类名,通过类加载器加载类名
- 对类型进行匹配,若符合匹配规则,则将其放入内部集合中
这里我们要注意,在前面我们分析Configuration对象的创建时,就已经默认注册了很多别名,可以回到文章开头看看。
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>
解析过程分析如下:
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); } } }
首先是获取配置,然后再解析拦截器类型,并实例化拦截器。最后向拦截器中设置属性,并将拦截器添加到 Configuration 中。
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,并实例化拦截器 Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance(); // 设置属性 interceptorInstance.setProperties(properties); // 添加拦截器到 Configuration 中 configuration.addInterceptor(interceptorInstance); } } } public void addInterceptor(Interceptor interceptor) { //添加到Configuration的interceptorChain属性中 this.interceptorChain.addInterceptor(interceptor); }
我们来看看InterceptorChain
public class InterceptorChain { private final List<Interceptor> interceptors = new ArrayList(); public InterceptorChain() { } public Object pluginAll(Object target) { Interceptor interceptor; for(Iterator i$ = this.interceptors.iterator(); i$.hasNext(); target = interceptor.plugin(target)) { interceptor = (Interceptor)i$.next(); } return target; } public void addInterceptor(Interceptor interceptor) { this.interceptors.add(interceptor); } public List<Interceptor> getInterceptors() { return Collections.unmodifiableList(this.interceptors); } }
实际上是一个 interceptors 集合,关于插件的原理我们后面再讲。
解析 environments 配置
在 MyBatis 中,事务管理器和数据源是配置在 environments 中的。它们的配置大致如下:
<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>
我们来看看environmentsElement方法
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 TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager")); // 将environment中的dataSource标签转换为DataSourceFactory对象 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()); } } } }
看看TransactionFactory和 DataSourceFactory的获取
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."); } }
<transactionManager type="JDBC"/>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
<dataSource type="POOLED">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
我们来看看PooledDataSourceFactory和UnpooledDataSourceFactory
public class UnpooledDataSourceFactory implements DataSourceFactory { private static final String DRIVER_PROPERTY_PREFIX = "driver."; private static final int DRIVER_PROPERTY_PREFIX_LENGTH = "driver.".length(); //创建UnpooledDataSource实例 protected DataSource dataSource = new UnpooledDataSource(); public DataSource getDataSource() { return this.dataSource; } //略 } //继承UnpooledDataSourceFactory public class PooledDataSourceFactory extends UnpooledDataSourceFactory { public PooledDataSourceFactory() { //创建PooledDataSource实例 this.dataSource = new PooledDataSource(); } }
我们发现 UnpooledDataSourceFactory 创建的dataSource是 UnpooledDataSource,PooledDataSourceFactory创建的 dataSource是PooledDataSource
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,我们下一篇文章会详解介绍这个方法
private void mapperElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { if ("package".equals(child.getName())) { String mapperPackage = child.getStringAttribute("name"); configuration.addMappers(mapperPackage); } else { String resource = child.getStringAttribute("resource"); String url = child.getStringAttribute("url"); String mapperClass = child.getStringAttribute("class"); if (resource != null && url == null && mapperClass == null) { ErrorContext.instance().resource(resource); InputStream inputStream = Resources.getResourceAsStream(resource); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments()); mapperParser.parse(); } else if (resource == null && url != null && mapperClass == null) { ErrorContext.instance().resource(url); InputStream inputStream = Resources.getUrlAsStream(url); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments()); mapperParser.parse(); } else if (resource == null && url == null && mapperClass != null) { Class<?> mapperInterface = Resources.classForName(mapperClass); configuration.addMapper(mapperInterface); } else { throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one."); } } } } }
创建DefaultSqlSessionFactory
到此为止XMLConfigBuilder的parse方法中的重要步骤都过了一遍了,然后返回的就是一个完整的Configuration对象了,最后通过SqlSessionFactoryBuilder的build的重载方法创建了一个SqlSessionFactory实例DefaultSqlSessionFactory,我们来看看
public SqlSessionFactory build(Configuration config) { //创建DefaultSqlSessionFactory实例 return new DefaultSqlSessionFactory(config); } public class DefaultSqlSessionFactory implements SqlSessionFactory { private final Configuration configuration; //只是将configuration设置为其属性 public DefaultSqlSessionFactory(Configuration configuration) { this.configuration = configuration; } //略 }
原文链接:https://www.cnblogs.com/java-chen-hao/p/11743430.html
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