前一章节已经介绍了，把方法分解成什么样子来分析，这里先来分析一个方法resultMapElements，在这个方法前还有cacheRefElement与cacheElement，但是由于配置文件中没有配置这2项，所以这里就先跳过。而parameterMapElement在最新的MyBatis中是过时的，也先跳过，以后可以在补充。
1 配置文件
<resultMap id="BaseResultMap" type="cn.vansky.schedule.time.role.bo.Role"> <id column="Id" property="id" jdbcType="INTEGER" /> <result column="role_name" property="roleName" jdbcType="VARCHAR" /> <result column="role_remark" property="roleRemark" jdbcType="VARCHAR" /> <result column="is_delete" property="isDelete" jdbcType="TINYINT" /> <result column="operation_user_name" property="operationUserName" jdbcType="VARCHAR" /> <result column="operation_time" property="operationTime" jdbcType="TIMESTAMP" /> </resultMap>
这里是使用自己扩展MyBatis的自动生成代码，生成的resultMap配置。
2 代码
private void resultMapElements(List<XNode> list) throws Exception {
for (XNode resultMapNode : list) {
try {
resultMapElement(resultMapNode);
} catch (IncompleteElementException e) {
// ignore, it will be retried
}
}
}
private ResultMap resultMapElement(XNode resultMapNode) throws Exception {
return resultMapElement(resultMapNode, Collections.<ResultMapping> emptyList());
}
这里是获取当前文件中所有resultMap对应的XML，然后分别对每个resultMap进行处理。这里会去捕获一个专门的异常，目前还不清楚是起什么作用，先继续往下分析。
3 方法resultMapElement
// resultMapNode是对应的resuleMap的XML信息，这里首先获取配置中的id，如果没有就自动生成一个id
String id = resultMapNode.getStringAttribute("id", resultMapNode.getValueBasedIdentifier());
// 那么这行很明显是获取type了，如果没有就获取ofType，还没有就获取resultType，还是没有就获取javaType
String type = resultMapNode.getStringAttribute("type",
resultMapNode.getStringAttribute("ofType",
resultMapNode.getStringAttribute("resultType", resultMapNode.getStringAttribute("javaType"))));
// 猜想是获取继承的父类
String extend = resultMapNode.getStringAttribute("extends");
//
Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping");
// 获取type对应的Class
Class<?> typeClass = resolveClass(type);
Discriminator discriminator = null;
List<ResultMapping> resultMappings = new ArrayList<ResultMapping>();
// 这里additionalResultMappings是空列表，而不是null
resultMappings.addAll(additionalResultMappings);
// 获取子节点id及result
List<XNode> resultChildren = resultMapNode.getChildren();
for (XNode resultChild : resultChildren) {
if ("constructor".equals(resultChild.getName())) {
processConstructorElement(resultChild, typeClass, resultMappings);
} else if ("discriminator".equals(resultChild.getName())) {
discriminator = processDiscriminatorElement(resultChild, typeClass, resultMappings);
} else {
// id与result都走这里
ArrayList<ResultFlag> flags = new ArrayList<ResultFlag>();
if ("id".equals(resultChild.getName())) {
flags.add(ResultFlag.ID);
}
resultMappings.add(buildResultMappingFromContext(resultChild, typeClass, flags));
}
}
4 buildResultMappingFromContext
以下都是以ID为例，进行分析。
private ResultMapping buildResultMappingFromContext(XNode context, Class<?> resultType, ArrayList<ResultFlag> flags) throws Exception {
// id
String property = context.getStringAttribute("property");
// Id
String column = context.getStringAttribute("column");
// null
String javaType = context.getStringAttribute("javaType");
// INTEGER
String jdbcType = context.getStringAttribute("jdbcType");
// null
String nestedSelect = context.getStringAttribute("select");
// null
String nestedResultMap = context.getStringAttribute("resultMap",
processNestedResultMappings(context, Collections.<ResultMapping> emptyList()));
// null
String notNullColumn = context.getStringAttribute("notNullColumn");
// null
String columnPrefix = context.getStringAttribute("columnPrefix");
// null
String typeHandler = context.getStringAttribute("typeHandler");
// null
String resulSet = context.getStringAttribute("resultSet");
// null
String foreignColumn = context.getStringAttribute("foreignColumn");
// false
boolean lazy = "lazy".equals(context.getStringAttribute("fetchType", configuration.isLazyLoadingEnabled() ? "lazy" : "eager"));
// null
Class<?> javaTypeClass = resolveClass(javaType);
@SuppressWarnings("unchecked")
// null
Class<? extends TypeHandler<?>> typeHandlerClass = (Class<? extends TypeHandler<?>>) resolveClass(typeHandler);
// 获取到JdbcType
JdbcType jdbcTypeEnum = resolveJdbcType(jdbcType);
// 这里就会构建生成一个ResultMapping
return builderAssistant.buildResultMapping(resultType, property, column, javaTypeClass, jdbcTypeEnum, nestedSelect, nestedResultMap, notNullColumn, columnPrefix, typeHandlerClass, flags, resulSet, foreignColumn, lazy);
}
5 MapperBuilderAssistant的buildResultMapping方法
public ResultMapping buildResultMapping(
Class<?> resultType,
String property,
String column,
Class<?> javaType,
JdbcType jdbcType,
String nestedSelect,
String nestedResultMap,
String notNullColumn,
String columnPrefix,
Class<? extends TypeHandler<?>> typeHandler,
List<ResultFlag> flags,
String resultSet,
String foreignColumn,
boolean lazy) {
// 这里如果配置中有javaType属性直接返回，否则通过type配置的类及属性获取对应的Class
Class<?> javaTypeClass = resolveResultJavaType(resultType, property, javaType);
// 获取类型处理器
TypeHandler<?> typeHandlerInstance = resolveTypeHandler(javaTypeClass, typeHandler);
//
List<ResultMapping> composites = parseCompositeColumnName(column);
if (composites.size() > 0) column = null;
// 初始化一些内部信息
ResultMapping.Builder builder = new ResultMapping.Builder(configuration, property, column, javaTypeClass);
builder.jdbcType(jdbcType);
builder.nestedQueryId(applyCurrentNamespace(nestedSelect, true));
builder.nestedResultMapId(applyCurrentNamespace(nestedResultMap, true));
builder.resultSet(resultSet);
builder.typeHandler(typeHandlerInstance);
builder.flags(flags == null ? new ArrayList<ResultFlag>() : flags);
builder.composites(composites);
builder.notNullColumns(parseMultipleColumnNames(notNullColumn));
builder.columnPrefix(columnPrefix);
builder.foreignColumn(foreignColumn);
builder.lazy(lazy);
return builder.build();
}
6 ResultMapping
6.1 属性
/** 全局配类 */ private Configuration configuration; /** id */ private String property; /** Id */ private String column; /** javaType */ private Class<?> javaType; /** JdbcType */ private JdbcType jdbcType; /** 类型处理器 */ private TypeHandler<?> typeHandler; private String nestedResultMapId; private String nestedQueryId; private Set<String> notNullColumns; private String columnPrefix; private List<ResultFlag> flags; private List<ResultMapping> composites; private String resultSet; private String foreignColumn; /** false */ private boolean lazy;
MyBatis的地址http://mybatis.github.io/mybatis-3/zh/sqlmap-xml.html#Result_Maps这里有很多例子，喜欢的童鞋可以多去研究一下。
当对id及result都遍历以后，会生成List<ResultMapping>。
ResultMapResolver resultMapResolver = new ResultMapResolver(builderAssistant, id, typeClass, extend, discriminator, resultMappings, autoMapping);
try {
return resultMapResolver.resolve();
} catch (IncompleteElementException e) {
configuration.addIncompleteResultMap(resultMapResolver);
throw e;
}
如果这里解析失败会抛出前面出现的捕获异常，并把错误的解析放入Configuration(全局配置类)的Collection<ResultMapResolver> incompleteResultMaps = new LinkedList<ResultMapResolver>()。
7 MapperBuilderAssistant的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);
return resultMap;
}
这里没有具体介绍，还需要慢慢深究。下面来看最终的ResultMap信息。
8 ResultMap属性
private String id; private Class<?> type; private List<ResultMapping> resultMappings; private List<ResultMapping> idResultMappings; private List<ResultMapping> constructorResultMappings; private List<ResultMapping> propertyResultMappings; private Set<String> mappedColumns; private Discriminator discriminator; private boolean hasNestedResultMaps; private boolean hasNestedQueries; private Boolean autoMapping;
至此最终的ResultMap信息出来了。
总结：
这里很多东西，作者也是一点一点去研究，而且实际项目中的配置也不是特别的多，所以有些还待完善。
原文：http://my.oschina.net/u/1269959/blog/522346