MyBatis 之默认配置和 mapper.xml 解析

在 Spring Boot 自动配置中，实例化 SqlSessionFactory 对象的时候，最后 return factory.getObject(); 就是在这里，完成了 mapper.xml 的解析。

mapper.xml 的解析

这里正式解析用户配置的所有 mapper.xml

xmlMapperBuilder.parse();

public class SqlSessionFactoryBean
    implements FactoryBean<SqlSessionFactory>, InitializingBean, ApplicationListener<ApplicationEvent> {
    @Override
    public SqlSessionFactory getObject() throws Exception {
        if (this.sqlSessionFactory == null) {
            afterPropertiesSet();
        }

        return this.sqlSessionFactory;
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        notNull(dataSource, "Property 'dataSource' is required");
        notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
        state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
                "Property 'configuration' and 'configLocation' can not specified with together");

        this.sqlSessionFactory = buildSqlSessionFactory();
    }

    protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
        final Configuration targetConfiguration;
        XMLConfigBuilder xmlConfigBuilder = null;
        if (this.configuration != null) {
            targetConfiguration = this.configuration;
            if (targetConfiguration.getVariables() == null) {
                targetConfiguration.setVariables(this.configurationProperties);
            } else if (this.configurationProperties != null) {
                targetConfiguration.getVariables().putAll(this.configurationProperties);
            }
        } else if (this.configLocation != null) {
            xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
            targetConfiguration = xmlConfigBuilder.getConfiguration();
        } else {
            LOGGER.debug(
                    () -> "Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
            targetConfiguration = new Configuration();
            Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
        }

        Optional.ofNullable(this.objectFactory).ifPresent(targetConfiguration::setObjectFactory);
        Optional.ofNullable(this.objectWrapperFactory).ifPresent(targetConfiguration::setObjectWrapperFactory);
        Optional.ofNullable(this.vfs).ifPresent(targetConfiguration::setVfsImpl);

        if (hasLength(this.typeAliasesPackage)) {
            scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream()
                    .filter(clazz -> !clazz.isAnonymousClass()).filter(clazz -> !clazz.isInterface())
                    .filter(clazz -> !clazz.isMemberClass()).forEach(targetConfiguration.getTypeAliasRegistry()::registerAlias);
        }

        if (!isEmpty(this.typeAliases)) {
            Stream.of(this.typeAliases).forEach(typeAlias -> {
                targetConfiguration.getTypeAliasRegistry().registerAlias(typeAlias);
                LOGGER.debug(() -> "Registered type alias: '" + typeAlias + "'");
            });
        }

        if (!isEmpty(this.plugins)) {
            Stream.of(this.plugins).forEach(plugin -> {
                targetConfiguration.addInterceptor(plugin);
                LOGGER.debug(() -> "Registered plugin: '" + plugin + "'");
            });
        }

        if (hasLength(this.typeHandlersPackage)) {
            scanClasses(this.typeHandlersPackage, TypeHandler.class).stream().filter(clazz -> !clazz.isAnonymousClass())
                    .filter(clazz -> !clazz.isInterface()).filter(clazz -> !Modifier.isAbstract(clazz.getModifiers()))
                    .forEach(targetConfiguration.getTypeHandlerRegistry()::register);
        }

        if (!isEmpty(this.typeHandlers)) {
            Stream.of(this.typeHandlers).forEach(typeHandler -> {
                targetConfiguration.getTypeHandlerRegistry().register(typeHandler);
                LOGGER.debug(() -> "Registered type handler: '" + typeHandler + "'");
            });
        }

        targetConfiguration.setDefaultEnumTypeHandler(defaultEnumTypeHandler);

        if (!isEmpty(this.scriptingLanguageDrivers)) {
            Stream.of(this.scriptingLanguageDrivers).forEach(languageDriver -> {
                targetConfiguration.getLanguageRegistry().register(languageDriver);
                LOGGER.debug(() -> "Registered scripting language driver: '" + languageDriver + "'");
            });
        }
        Optional.ofNullable(this.defaultScriptingLanguageDriver)
                .ifPresent(targetConfiguration::setDefaultScriptingLanguage);

        if (this.databaseIdProvider != null) {// fix #64 set databaseId before parse mapper xmls
            try {
                targetConfiguration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
            } catch (SQLException e) {
                throw new NestedIOException("Failed getting a databaseId", e);
            }
        }

        Optional.ofNullable(this.cache).ifPresent(targetConfiguration::addCache);

        if (xmlConfigBuilder != null) {
            try {
                xmlConfigBuilder.parse();
                LOGGER.debug(() -> "Parsed configuration file: '" + this.configLocation + "'");
            } catch (Exception ex) {
                throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
            } finally {
                ErrorContext.instance().reset();
            }
        }

        targetConfiguration.setEnvironment(new Environment(this.environment,
                this.transactionFactory == null ? new SpringManagedTransactionFactory() : this.transactionFactory,
                this.dataSource));

        if (this.mapperLocations != null) {
            if (this.mapperLocations.length == 0) {
                LOGGER.warn(() -> "Property 'mapperLocations' was specified but matching resources are not found.");
            } else {
                for (Resource mapperLocation : this.mapperLocations) {
                    if (mapperLocation == null) {
                        continue;
                    }
                    try {
                        XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
                                targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
                        // 这里正式解析用户配置的所有 mapper.xml
                        xmlMapperBuilder.parse();
                    } catch (Exception e) {
                        throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
                    } finally {
                        ErrorContext.instance().reset();
                    }
                    LOGGER.debug(() -> "Parsed mapper file: '" + mapperLocation + "'");
                }
            }
        } else {
            LOGGER.debug(() -> "Property 'mapperLocations' was not specified.");
        }

        return this.sqlSessionFactoryBuilder.build(targetConfiguration);
    }
}

XMLMapperBuilder.parse();

public class XMLMapperBuilder extends BaseBuilder {
    public void parse() {
        if (!configuration.isResourceLoaded(resource)) {
            // 这里解析 mapper.xml 中的所有标签，并封装为对象返回
            configurationElement(parser.evalNode("/mapper"));
            configuration.addLoadedResource(resource);
            // MapperProxyFactory 主要看这里
            bindMapperForNamespace();
        }

        parsePendingResultMaps();
        parsePendingCacheRefs();
        parsePendingStatements();
    }

    private void configurationElement(XNode context) {
        try {
            String namespace = context.getStringAttribute("namespace");
            if (namespace == null || namespace.isEmpty()) {
                throw new BuilderException("Mapper's namespace cannot be empty");
            }
            builderAssistant.setCurrentNamespace(namespace);
            cacheRefElement(context.evalNode("cache-ref"));
            cacheElement(context.evalNode("cache"));
            parameterMapElement(context.evalNodes("/mapper/parameterMap"));
            resultMapElements(context.evalNodes("/mapper/resultMap"));
            sqlElement(context.evalNodes("/mapper/sql"));
            buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
        } catch (Exception e) {
            throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
        }
    }

    private void bindMapperForNamespace() {
        String namespace = builderAssistant.getCurrentNamespace();
        if (namespace != null) {
            Class<?> boundType = null;
            try {
                boundType = Resources.classForName(namespace);
            } catch (ClassNotFoundException e) {
                // ignore, bound type is not required
            }
            if (boundType != null && !configuration.hasMapper(boundType)) {
                // Spring may not know the real resource name so we set a flag
                // to prevent loading again this resource from the mapper interface
                // look at MapperAnnotationBuilder#loadXmlResource
                configuration.addLoadedResource("namespace:" + namespace);
                // MapperProxyFactory 主要看这里
                configuration.addMapper(boundType);
            }
        }
    }
}

public class Configuration {
    public <T> void addMapper(Class<T> type) {
        mapperRegistry.addMapper(type);
    }
}

public class MapperRegistry {
    public <T> void addMapper(Class<T> type) {
        if (type.isInterface()) {
            if (hasMapper(type)) {
                throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
            }
            boolean loadCompleted = false;
            try {
                // 主要是这里，建立的 Mapper 类的映射和 MapperProxyFactory，在生成代理对象的时候，就可以直接获取到 MapperProxyFactory
                knownMappers.put(type, new MapperProxyFactory<>(type));
                // It's important that the type is added before the parser is run
                // otherwise the binding may automatically be attempted by the
                // mapper parser. If the type is already known, it won't try.
                MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
                // 这里是多 @Mapper 类中的一些注解的支持，如：@Select, @ResultMap 等注解
                parser.parse();
                loadCompleted = true;
            } finally {
                if (!loadCompleted) {
                    knownMappers.remove(type);
                }
            }
        }
    }
}

至此，mapper.xml 中的标签解析完成，建立的 Mapper 类的映射和 MapperProxyFactory 完成。