在<MyBatis框架中Mapper映射配置的使用及原理解析(二) 配置篇 SqlSessionFactoryBuilder，XMLConfigBuilder> 一文中，我们知道mybatis配置文件是由XMLConfigBuilder来解析的,看以下代码：
public Configuration parse() {
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
private void parseConfiguration(XNode root) {
try {
propertiesElement(root.evalNode("properties")); //issue #117 read properties first
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
settingsElement(root.evalNode("settings"));
environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
//解析mapper
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
可以看到解析mapper文件的加载解析i是从 mapperElement(root.evalNode("mappers")); 开始处理的。
我们继续看mapperElement(XNode parent)方法的代码：
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) { //解析package扫描指定package下的所有mapper接口
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else { //解析mapper节点
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.");
}
}
}
}
}
可以看到，mybatisConfig.xml配置下的mappers节点有2种子节点：package节点和mapper节点，我这里先讨论xml的模式，先看mapper节点。
mapper节点配置有3个属性：resource,url,class。他们处理的优先级依次是resource,url,class，3个属性只处理一种。resource,url属性映射的是xml的路径，class是mapper接口的类路径。
从源码中我们看到，通过读取resource或url属性得到xml的访问路径后，交给XMLMapperBuilder对象来解析。
我们查看XMLMapperBuilder的parse方法:
public void parse() {
if (!configuration.isResourceLoaded(resource)) {
configurationElement(parser.evalNode("/mapper")); //从mapper节点开始解析
configuration.addLoadedResource(resource); //标记已经加载了次xml资源
bindMapperForNamespace(); //绑定到命名空间
}
parsePendingResultMaps(); //将resultMap映射信息转换成ResultMap对象
parsePendingChacheRefs(); //将cache映射信息转换成Cache对象
parsePendingStatements(); //将sql映射转换成MappedStatement
}
//解析xml
private void configurationElement(XNode context) {
try {
String namespace = context.getStringAttribute("namespace");
if (namespace.equals("")) {
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. Cause: " + e, e);
}
}
//绑定到命名空间
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) {
if (!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);
configuration.addMapper(boundType);
}
}
}
}
其中configurationElement(XNode context)负责解析所有的xml元素，bindMapperForNamespace() 绑定到命名空间
而parsePendingResultMaps(), parsePendingChacheRefs(), parsePendingStatements()则分别将对应的xml信息转换成ResultMap对象，Cache对象和MappedStatement对象。
ResultMap的处理
private void parsePendingResultMaps() {
Collection<ResultMapResolver> incompleteResultMaps = configuration.getIncompleteResultMaps();
synchronized (incompleteResultMaps) {
Iterator<ResultMapResolver> iter = incompleteResultMaps.iterator();
while (iter.hasNext()) {
try {
iter.next().resolve(); //实际处理的是ResultMapResolver.resolve()方法
iter.remove();
} catch (IncompleteElementException e) {
// ResultMap is still missing a resource...
}
}
}
}
看代码得知，实际处理的是ResultMapResolver.resolve()方法
package org.apache.ibatis.builder; import java.util.List; import org.apache.ibatis.mapping.Discriminator;
import org.apache.ibatis.mapping.ResultMap;
import org.apache.ibatis.mapping.ResultMapping; /**
* @author Eduardo Macarron
*/
public class ResultMapResolver {
private final MapperBuilderAssistant assistant;
private String id;
private Class<?> type;
private String extend;
private Discriminator discriminator;
private List<ResultMapping> resultMappings;
private Boolean autoMapping; public ResultMapResolver(MapperBuilderAssistant assistant, String id, Class<?> type, String extend, Discriminator discriminator, List<ResultMapping> resultMappings, Boolean autoMapping) {
this.assistant = assistant;
this.id = id;
this.type = type;
this.extend = extend;
this.discriminator = discriminator;
this.resultMappings = resultMappings;
this.autoMapping = autoMapping;
} public ResultMap resolve() {
return assistant.addResultMap(this.id, this.type, this.extend, this.discriminator, this.resultMappings, this.autoMapping);
} }
接着发现最终调用的是MapperBuilderAssistant.addResultMap 方法
public ResultMap addResultMap(
String id,
Class<?> type,
String extend,
Discriminator discriminator,
List<ResultMapping> resultMappings,
Boolean autoMapping) {
id = applyCurrentNamespace(id, false);
extend = applyCurrentNamespace(extend, true); ResultMap.Builder resultMapBuilder = new ResultMap.Builder(configuration, id, type, resultMappings, autoMapping);
if (extend != null) {
if (!configuration.hasResultMap(extend)) {
throw new IncompleteElementException("Could not find a parent resultmap with id '" + extend + "'");
}
ResultMap resultMap = configuration.getResultMap(extend);
List<ResultMapping> extendedResultMappings = new ArrayList<ResultMapping>(resultMap.getResultMappings());
extendedResultMappings.removeAll(resultMappings);
// Remove parent constructor if this resultMap declares a constructor.
boolean declaresConstructor = false;
for (ResultMapping resultMapping : resultMappings) {
if (resultMapping.getFlags().contains(ResultFlag.CONSTRUCTOR)) {
declaresConstructor = true;
break;
}
}
if (declaresConstructor) {
Iterator<ResultMapping> extendedResultMappingsIter = extendedResultMappings.iterator();
while (extendedResultMappingsIter.hasNext()) {
if (extendedResultMappingsIter.next().getFlags().contains(ResultFlag.CONSTRUCTOR)) {
extendedResultMappingsIter.remove();
}
}
}
resultMappings.addAll(extendedResultMappings);
}
resultMapBuilder.discriminator(discriminator);
ResultMap resultMap = resultMapBuilder.build();
configuration.addResultMap(resultMap); //添加到Configuration
return resultMap;
}
Cache的处理
private void parsePendingChacheRefs() {
Collection<CacheRefResolver> incompleteCacheRefs = configuration.getIncompleteCacheRefs();
synchronized (incompleteCacheRefs) {
Iterator<CacheRefResolver> iter = incompleteCacheRefs.iterator();
while (iter.hasNext()) {
try {
iter.next().resolveCacheRef();
iter.remove();
} catch (IncompleteElementException e) {
// Cache ref is still missing a resource...
}
}
}
}
调用的是org.apache.ibatis.builder.CacheRefResolver.resolveCacheRef()方法：
public Cache resolveCacheRef() {
return assistant.useCacheRef(cacheRefNamespace);
}
最终调用org.apache.ibatis.builder.useCacheRef(String namespace)方法创建Cache对象并添加到Configuration：
public Cache useCacheRef(String namespace) {
if (namespace == null) {
throw new BuilderException("cache-ref element requires a namespace attribute.");
}
try {
unresolvedCacheRef = true;
Cache cache = configuration.getCache(namespace);
if (cache == null) {
throw new IncompleteElementException("No cache for namespace '" + namespace + "' could be found.");
}
currentCache = cache;
unresolvedCacheRef = false;
return cache;
} catch (IllegalArgumentException e) {
throw new IncompleteElementException("No cache for namespace '" + namespace + "' could be found.", e);
}
}
MappedStatement的处理
从parsePendingStatements()方法开始跟踪
private void parsePendingStatements() {
Collection<XMLStatementBuilder> incompleteStatements = configuration.getIncompleteStatements();
synchronized (incompleteStatements) {
Iterator<XMLStatementBuilder> iter = incompleteStatements.iterator();
while (iter.hasNext()) {
try {
iter.next().parseStatementNode(); //调用XMLStatementBuilder的parseStatementNode方法
iter.remove();
} catch (IncompleteElementException e) {
// Statement is still missing a resource...
}
}
}
}
然后调用org.apache.ibatis.builder.xml.XMLStatementBuilder的parseStatementNode方法
public void parseStatementNode() {
String id = context.getStringAttribute("id");
String databaseId = context.getStringAttribute("databaseId");
if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) return;
Integer fetchSize = context.getIntAttribute("fetchSize");
Integer timeout = context.getIntAttribute("timeout");
String parameterMap = context.getStringAttribute("parameterMap");
String parameterType = context.getStringAttribute("parameterType");
Class<?> parameterTypeClass = resolveClass(parameterType);
String resultMap = context.getStringAttribute("resultMap");
String resultType = context.getStringAttribute("resultType");
String lang = context.getStringAttribute("lang");
LanguageDriver langDriver = getLanguageDriver(lang);
Class<?> resultTypeClass = resolveClass(resultType);
String resultSetType = context.getStringAttribute("resultSetType");
StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
String nodeName = context.getNode().getNodeName();
SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
boolean useCache = context.getBooleanAttribute("useCache", isSelect);
boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);
// Include Fragments before parsing
XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
includeParser.applyIncludes(context.getNode());
// Parse selectKey after includes and remove them.
processSelectKeyNodes(id, parameterTypeClass, langDriver);
// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
String resultSets = context.getStringAttribute("resultSets");
String keyProperty = context.getStringAttribute("keyProperty");
String keyColumn = context.getStringAttribute("keyColumn");
KeyGenerator keyGenerator;
String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
if (configuration.hasKeyGenerator(keyStatementId)) {
keyGenerator = configuration.getKeyGenerator(keyStatementId);
} else {
keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
? new Jdbc3KeyGenerator() : new NoKeyGenerator();
}
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}
最后MappedStatement由org.apache.ibatis.builder.MapperBuilderAssistant的addMappedStatement方法创建，并加入到Configuration
public MappedStatement addMappedStatement(
String id,
SqlSource sqlSource,
StatementType statementType,
SqlCommandType sqlCommandType,
Integer fetchSize,
Integer timeout,
String parameterMap,
Class<?> parameterType,
String resultMap,
Class<?> resultType,
ResultSetType resultSetType,
boolean flushCache,
boolean useCache,
boolean resultOrdered,
KeyGenerator keyGenerator,
String keyProperty,
String keyColumn,
String databaseId,
LanguageDriver lang,
String resultSets) { if (unresolvedCacheRef) throw new IncompleteElementException("Cache-ref not yet resolved"); id = applyCurrentNamespace(id, false);
boolean isSelect = sqlCommandType == SqlCommandType.SELECT; MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType);
statementBuilder.resource(resource);
statementBuilder.fetchSize(fetchSize);
statementBuilder.statementType(statementType);
statementBuilder.keyGenerator(keyGenerator);
statementBuilder.keyProperty(keyProperty);
statementBuilder.keyColumn(keyColumn);
statementBuilder.databaseId(databaseId);
statementBuilder.lang(lang);
statementBuilder.resultOrdered(resultOrdered);
statementBuilder.resulSets(resultSets);
setStatementTimeout(timeout, statementBuilder); setStatementParameterMap(parameterMap, parameterType, statementBuilder);
setStatementResultMap(resultMap, resultType, resultSetType, statementBuilder);
setStatementCache(isSelect, flushCache, useCache, currentCache, statementBuilder); MappedStatement statement = statementBuilder.build();
configuration.addMappedStatement(statement);
return statement;
}
Mapper xml部分的解析，暂时粗略的写这么多，后续我们还将讲解package包的扫描和指定class的mapper的情况。