从MyBatis入门使用文章中可知，MyBatis在使用前有一些前置的配置，并且每个Mapper接口需要对应一个 *Mapper.xml 的配置文件，这篇文章将解析 Mybatis 读取配置文件的过程。
public class Main {
public static void main(String[] args) {
String resource = "mybatis-config.xml";
SqlSession session = null;
try {
InputStream inputStream = Resources.getResourceAsStream(resource);
// 读取配置的过程在 build 方法过程中
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
System.out.println(sqlSessionFactory);
session = sqlSessionFactory.openSession();
ActorMapper actorMapper = session.getMapper(ActorMapper.class);
Actor actor = actorMapper.selectOneActor(1);
System.out.println(actor);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (session != null) {
session.close();
}
}
}
}
解析 mybatis-config.xml
mybatis-config.xml 配置文件：
Configuration
public class Configuration {
protected Environment environment;
protected boolean safeRowBoundsEnabled;
protected boolean safeResultHandlerEnabled;
protected boolean mapUnderscoreToCamelCase;
protected boolean aggressiveLazyLoading;
protected boolean multipleResultSetsEnabled;
protected boolean useGeneratedKeys;
protected boolean useColumnLabel;
protected boolean cacheEnabled;
protected boolean callSettersOnNulls;
protected boolean useActualParamName;
protected boolean returnInstanceForEmptyRow;
protected boolean shrinkWhitespacesInSql;
protected String logPrefix;
protected Class logImpl;
protected Class vfsImpl;
protected Class defaultSqlProviderType;
// 一级缓存配置，默认值为 SESSION，表示在同一个 session 连接中执行同一个SQL会使用上一次的查询结果缓存，
// 当配置成 STATEMENT 时不使用一级缓存
protected LocalCacheScope localCacheScope;
protected JdbcType jdbcTypeForNull;
protected Set lazyLoadTriggerMethods;
protected Integer defaultStatementTimeout;
protected Integer defaultFetchSize;
protected ResultSetType defaultResultSetType;
protected ExecutorType defaultExecutorType;
protected AutoMappingBehavior autoMappingBehavior;
protected AutoMappingUnknownColumnBehavior autoMappingUnknownColumnBehavior;
protected Properties variables;
protected ReflectorFactory reflectorFactory;
protected ObjectFactory objectFactory;
protected ObjectWrapperFactory objectWrapperFactory;
protected boolean lazyLoadingEnabled;
protected ProxyFactory proxyFactory;
protected String databaseId;
protected Class configurationFactory;
protected final MapperRegistry mapperRegistry;
protected final InterceptorChain interceptorChain;
protected final TypeHandlerRegistry typeHandlerRegistry;
protected final TypeAliasRegistry typeAliasRegistry;
protected final LanguageDriverRegistry languageRegistry;
protected final Map mappedStatements;
protected final Map caches;
protected final Map resultMaps;
protected final Map parameterMaps;
protected final Map keyGenerators;
protected final Set loadedResources;
protected final Map sqlFragments;
protected final Collection incompleteStatements;
protected final Collection incompleteCacheRefs;
protected final Collection incompleteResultMaps;
protected final Collection incompleteMethods;
protected final Map cacheRefMap;
// 构造方法给 Configuration 赋的是默认值
public Configuration() {
this.safeResultHandlerEnabled = true;
this.multipleResultSetsEnabled = true;
this.useColumnLabel = true;
this.cacheEnabled = true;
this.useActualParamName = true;
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.lazyLoadingEnabled = false;
this.proxyFactory = new JavassistProxyFactory();
this.mapperRegistry = new MapperRegistry(this);
this.interceptorChain = new InterceptorChain();
this.typeHandlerRegistry = new TypeHandlerRegistry(this);
this.typeAliasRegistry = new TypeAliasRegistry();
this.languageRegistry = new LanguageDriverRegistry();
this.mappedStatements = (new Configuration.StrictMap("Mapped Statements collection")).conflictMessageProducer((savedValue, targetValue) -> {
return ". please check " + savedValue.getResource() + " and " + targetValue.getResource();
});
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();
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);
}
}
SqlSessionFactoryBuilder build 方法
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
SqlSessionFactory var5;
try {
// 构建解析 XML 的对象 XMLConfigBuilder
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
var5 = this.build(parser.parse());
} catch (Exception var14) {
throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
} finally {
ErrorContext.instance().reset();
try {
inputStream.close();
} catch (IOException var13) {
}
}
return var5;
}
XMLConfigBuilder
public class XMLConfigBuilder extends BaseBuilder {
private boolean parsed;
private final XPathParser parser;
private String environment;
private final ReflectorFactory localReflectorFactory;
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
// 给 Configuration 赋初始值
super(new Configuration());
this.localReflectorFactory = new DefaultReflectorFactory();
ErrorContext.instance().resource("SQL Mapper Configuration");
this.configuration.setVariables(props);
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
}
XMLConfigBuilder 父类 BaseBuilder
public abstract class BaseBuilder {
// 解析xml后的配置都存放在 Configuration 中
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();
}
}
重点看下 XMLConfigBuilder parse 方法，此方法为解析 mybatis-config.xml 文件的入口
XMLConfigBuilder parse 方法，此方法返回 Configuration 对象作为 build 方法入参
public Configuration parse() {
if (this.parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
} else {
this.parsed = true;
this.parseConfiguration(this.parser.evalNode("/configuration"));
return this.configuration;
}
}
XMLConfigBuilder parseConfiguration 方法
对照 mybatis-config.xml 文件，读取对应的配置项
private void parseConfiguration(XNode root) {
try {
this.propertiesElement(root.evalNode("properties"));
Properties settings = this.settingsAsProperties(root.evalNode("settings"));
this.loadCustomVfs(settings);
this.loadCustomLogImpl(settings);
this.typeAliasesElement(root.evalNode("typeAliases"));
this.pluginElement(root.evalNode("plugins"));
this.objectFactoryElement(root.evalNode("objectFactory"));
this.objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
this.reflectorFactoryElement(root.evalNode("reflectorFactory"));
this.settingsElement(settings);
this.environmentsElement(root.evalNode("environments"));
this.databaseIdProviderElement(root.evalNode("databaseIdProvider"));
this.typeHandlerElement(root.evalNode("typeHandlers"));
// 解析 配置
this.mapperElement(root.evalNode("mappers"));
} catch (Exception var3) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + var3, var3);
}
}
