前边在初始化SqlSessionFactory的时候，mapper映射的部分留了下来，现在来完成mapper映射的解析。
mapper映射就是根据xml中mappers标签，找到相应的mapper接口和mapper.xml生成代理类到spring容器。
常用的配置有三种情况：
1、接口信息进行配置：这种方式必须保证接口名（例如UserMapper）和xml名（UserMapper.xml）相同，还必须在同一个包中。因为是通过获取mapper中的class属性，拼接上.xml来读取UserMapper.xml，如果xml文件名不同或者不在同一个包中是无法读取到xml的。
<mappers>
<mapper class="org.mybatis.mappers.UserMapper"/>
<mapper class="org.mybatis.mappers.ProductMapper"/>
<mapper class="org.mybatis.mappers.ManagerMapper"/>
</mappers>
2、相对路径进行配置：这种方式不用保证同接口同包同名。但是要保证xml中的namespase和对应的接口名相同。
<mappers>
<mapper resource="org/mybatis/mappers/UserMapper.xml"/>
<mapper resource="org/mybatis/mappers/ProductMapper.xml"/>
<mapper resource="org/mybatis/mappers/ManagerMapper.xml"/>
</mappers>
3、接口所在包进行配置：这种方式和第一种方式要求一致，保证接口名（例如UserMapper）和xml名（UserMapper.xml）相同，还必须在同一个包中。
<mappers>
<package name="org.mybatis.mappers"/>
</mappers>
// XMLConfigBuilder
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
//包扫描的形式
if ("package".equals(child.getName())) {
// 获取 <package> 节点中的 name 属性
String mapperPackage = child.getStringAttribute("name");
// 从指定包中查找 所有的 mapper 接口，并根据 mapper 接口解析映射配置
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
//相对路径的方式
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());
// 解析映射文件
mapperParser.parse();
// 绝对路径方式，略过
} 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) {
// 通过 mapperClass 解析映射配置
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.");
}
}
}
}
}
上面代码对应上面几种方式的入口。
先来看以packae扫描的形式
//Configuration
public void addMappers(String packageName) {
mapperRegistry.addMappers(packageName);
}
//MapperRegistry
public void addMappers(String packageName) {
this.addMappers(packageName, Object.class);
}
public void addMappers(String packageName, Class<?> superType) {
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil();
resolverUtil.find(new IsA(superType), packageName);
Set<Class<? extends Class<?>>> mapperSet = resolverUtil.getClasses();
Iterator i$ = mapperSet.iterator();
while(i$.hasNext()) {
Class<?> mapperClass = (Class)i$.next();
//找出包下的所有mapper，挨个调用这个方法
//入口
this.addMapper(mapperClass);
}
}
public <T> void addMapper(Class<T> type) {
if (type.isInterface()) {//mapper是接口
if (this.hasMapper(type)) {
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
this.knownMappers.put(type, new MapperProxyFactory(type));
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(this.config, type);
parser.parse();//入口
loadCompleted = true;
} finally {
if (!loadCompleted) {
this.knownMappers.remove(type);
}
}
}
}
//mapper代理工厂map
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap();
//MapperAnnotationBuilder
public void parse() {
String resource = this.type.toString();
if (!this.configuration.isResourceLoaded(resource)) {
this.loadXmlResource();//入口
this.configuration.addLoadedResource(resource);
this.assistant.setCurrentNamespace(this.type.getName());
this.parseCache();
this.parseCacheRef();
Method[] methods = this.type.getMethods();
Method[] var3 = methods;
int var4 = methods.length;
for(int var5 = 0; var5 < var4; ++var5) {
Method method = var3[var5];
try {
if (!method.isBridge()) {
this.parseStatement(method);
}
} catch (IncompleteElementException var8) {
this.configuration.addIncompleteMethod(new MethodResolver(this, method));
}
}
}
this.parsePendingMethods();
}
private void loadXmlResource() {
if (!this.configuration.isResourceLoaded("namespace:" + this.type.getName())) {
String xmlResource = this.type.getName().replace('.', '/') + ".xml";
InputStream inputStream = null;
try {
inputStream = Resources.getResourceAsStream(this.type.getClassLoader(), xmlResource);
} catch (IOException var4) {
}
if (inputStream != null) {
XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, this.assistant.getConfiguration(), xmlResource, this.configuration.getSqlFragments(), this.type.getName());
xmlParser.parse();//入口
}
}
}
//XMLMapperBuilder
public void parse() {
// 检测映射文件是否已经被解析过
if (!configuration.isResourceLoaded(resource)) {
//解析mapper的方法入口
//入口
configurationElement(parser.evalNode("/mapper"));
// 添加资源路径到“已解析资源集合”中
configuration.addLoadedResource(resource);
// 通过命名空间绑定 Mapper 接口
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();
}
在 MyBatis 映射文件中，可以配置多种节点。比如
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mapper.EmployeeMapper">
<cache/>
<resultMap id="baseMap" type="entity.Employee">
<result property="id" column="id" jdbcType="INTEGER"></result>
<result property="name" column="name" jdbcType="VARCHAR"></result>
</resultMap>
<sql id="table">
employee
</sql>
<select id="getAll" resultMap="baseMap">
select * from <include refid="table"/> WHERE id = #{id}
</select>
<!-- <insert|update|delete/> -->
</mapper>
//XMLMapperBuilder
private void configurationElement(XNode context) {
try {
// 获取 mapper 命名空间，如 mapper.EmployeeMapper
String namespace = context.getStringAttribute("namespace");
if (namespace == null || namespace.equals("")) {
throw new BuilderException("Mapper's namespace cannot be empty");
}
// 设置命名空间到 builderAssistant 中
builderAssistant.setCurrentNamespace(namespace);
// 解析 <cache-ref> 节点
cacheRefElement(context.evalNode("cache-ref"));
// 解析 <cache> 节点
cacheElement(context.evalNode("cache"));
// 已废弃配置，这里不做分析
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
// 解析 <resultMap> 节点
resultMapElements(context.evalNodes("/mapper/resultMap"));
// 解析 <sql> 节点
sqlElement(context.evalNodes("/mapper/sql"));
// 解析 <select>、<insert>、<update>、<delete> 节点
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);
}
}
接下来就是解析mapper里的具体标签。
解析 cache 节点
MyBatis 提供了一、二级缓存，其中一级缓存是 SqlSession 级别的，默认为开启状态。二级缓存配置在映射文件中，使用者需要显示配置才能开启。如下：
<cache/>
也可以使用第三方缓存
<cache type="org.mybatis.caches.redis.RedisCache"/>
其中有一些属性可以选择
<cache eviction="LRU" flushInterval="60000" size="512" readOnly="true"/>
private void cacheElement(XNode context) throws Exception {
if (context != null) {
// 获取type属性，如果type没有指定就用默认的PERPETUAL(早已经注册过的别名的PerpetualCache)
String type = context.getStringAttribute("type", "PERPETUAL");
// 根据type从早已经注册的别名中获取对应的Class,PERPETUAL对应的Class是PerpetualCache.class
// 如果我们写了type属性，如type="org.mybatis.caches.redis.RedisCache"，这里将会得到RedisCache.class
Class<? extends Cache> typeClass = typeAliasRegistry.resolveAlias(type);
//获取淘汰方式，默认为LRU(早已经注册过的别名的LruCache)，最近最少使用到的先淘汰
String eviction = context.getStringAttribute("eviction", "LRU");
Class<? extends Cache> evictionClass = typeAliasRegistry.resolveAlias(eviction);
Long flushInterval = context.getLongAttribute("flushInterval");
Integer size = context.getIntAttribute("size");
boolean readWrite = !context.getBooleanAttribute("readOnly", false);
boolean blocking = context.getBooleanAttribute("blocking", false);
// 获取子节点配置
Properties props = context.getChildrenAsProperties();
// 构建缓存对象
//入口
builderAssistant.useNewCache(typeClass, evictionClass, flushInterval, size, readWrite, blocking, props);
}
}
public Cache useNewCache(Class<? extends Cache> typeClass,
Class<? extends Cache> evictionClass,Long flushInterval,
Integer size,boolean readWrite,boolean blocking,Properties props) {
// 使用建造模式构建缓存实例
Cache cache = new CacheBuilder(currentNamespace)
.implementation(valueOrDefault(typeClass, PerpetualCache.class))
.addDecorator(valueOrDefault(evictionClass, LruCache.class))
.clearInterval(flushInterval)
.size(size)
.readWrite(readWrite)
.blocking(blocking)
.properties(props)
.build();
// 添加缓存到 Configuration 对象中
configuration.addCache(cache);
// 设置 currentCache 属性，即当前使用的缓存
currentCache = cache;
return cache;
}
public Cache build() {
// 设置默认的缓存类型（PerpetualCache）和缓存装饰器（LruCache）
setDefaultImplementations();//入口1
// 通过反射创建缓存
//入口2
Cache cache = newBaseCacheInstance(implementation, id);
setCacheProperties(cache);
// 仅对内置缓存 PerpetualCache 应用装饰器
if (PerpetualCache.class.equals(cache.getClass())) {
// 遍历装饰器集合，应用装饰器
for (Class<? extends Cache> decorator : decorators) {
// 通过反射创建装饰器实例
cache = newCacheDecoratorInstance(decorator, cache);
// 设置属性值到缓存实例中
setCacheProperties(cache);
}
// 应用标准的装饰器，比如 LoggingCache、SynchronizedCache
cache = setStandardDecorators(cache);
} else if (!LoggingCache.class.isAssignableFrom(cache.getClass())) {
// 应用具有日志功能的缓存装饰器
cache = new LoggingCache(cache);
}
return cache;
}
private void setDefaultImplementations() {
if (this.implementation == null) {
//设置默认缓存类型为PerpetualCache
this.implementation = PerpetualCache.class;
if (this.decorators.isEmpty()) {
this.decorators.add(LruCache.class);
}
}
}
private Cache newBaseCacheInstance(Class<? extends Cache> cacheClass, String id) {
//获取构造器
Constructor cacheConstructor = this.getBaseCacheConstructor(cacheClass);
try {
//通过构造器实例化Cache
return (Cache)cacheConstructor.newInstance(id);
} catch (Exception var5) {
throw new CacheException("Could not instantiate cache implementation (" + cacheClass + "). Cause: " + var5, var5);
}
}
解析 resultMap 节点
private void resultMapElements(List<XNode> list) throws Exception {
// 遍历 <resultMap> 节点列表
for (XNode resultMapNode : list) {
try {
// 解析 resultMap 节点
//入口
resultMapElement(resultMapNode);
} catch (IncompleteElementException e) {
}
}
}
private ResultMap resultMapElement(XNode resultMapNode) throws Exception {
return resultMapElement(resultMapNode, Collections.<ResultMapping>emptyList());
}
private ResultMap resultMapElement(XNode resultMapNode, List<ResultMapping> additionalResultMappings) throws Exception {
ErrorContext.instance().activity("processing " + resultMapNode.getValueBasedIdentifier());
// 获取 id 和 type 属性
String id = resultMapNode.getStringAttribute("id", resultMapNode.getValueBasedIdentifier());
String type = resultMapNode.getStringAttribute("type",
resultMapNode.getStringAttribute("ofType",
resultMapNode.getStringAttribute("resultType",
resultMapNode.getStringAttribute("javaType"))));
// 获取 extends 和 autoMapping
String extend = resultMapNode.getStringAttribute("extends");
Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping");
// 获取 type 属性对应的类型
Class<?> typeClass = resolveClass(type);
Discriminator discriminator = null;
//创建ResultMapping集合，对应resultMap子节点的id和result节点
List<ResultMapping> resultMappings = new ArrayList<ResultMapping>();
resultMappings.addAll(additionalResultMappings);
// 获取并遍历 <resultMap> 的子节点列表
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 {
List<ResultFlag> flags = new ArrayList<ResultFlag>();
if ("id".equals(resultChild.getName())) {
// 添加 ID 到 flags 集合中
flags.add(ResultFlag.ID);
}
// 解析 id 和 result 节点，将id或result节点生成相应的 ResultMapping，将ResultMapping添加到resultMappings集合中
//入口
resultMappings.add(buildResultMappingFromContext(resultChild, typeClass, flags));
}
}
//创建ResultMapResolver对象
ResultMapResolver resultMapResolver = new ResultMapResolver(builderAssistant, id, typeClass, extend,
discriminator, resultMappings, autoMapping);
try {
// 根据前面获取到的信息构建 ResultMap 对象
return resultMapResolver.resolve();
} catch (IncompleteElementException e) {
configuration.addIncompleteResultMap(resultMapResolver);
throw e;
}
}
在
private ResultMapping buildResultMappingFromContext(XNode context, Class<?> resultType, List<ResultFlag> flags) throws Exception {
String property;
// 根据节点类型获取 name 或 property 属性
if (flags.contains(ResultFlag.CONSTRUCTOR)) {
property = context.getStringAttribute("name");
} else {
property = context.getStringAttribute("property");
}
// 获取其他各种属性
String column = context.getStringAttribute("column");
String javaType = context.getStringAttribute("javaType");
String jdbcType = context.getStringAttribute("jdbcType");
String nestedSelect = context.getStringAttribute("select");
/*
* 解析 resultMap 属性，该属性出现在 <association> 和 <collection> 节点中。
* 若这两个节点不包含 resultMap 属性，则调用 processNestedResultMappings 方法,递归调用resultMapElement解析<association> 和 <collection>的嵌套节点，生成resultMap，并返回resultMap.getId();
* 如果包含resultMap属性，则直接获取其属性值，这个属性值对应一个resultMap节点
*/
//入口
String nestedResultMap = context.getStringAttribute("resultMap", processNestedResultMappings(context, Collections.<ResultMapping>emptyList()));
String notNullColumn = context.getStringAttribute("notNullColumn");
String columnPrefix = context.getStringAttribute("columnPrefix");
String typeHandler = context.getStringAttribute("typeHandler");
String resultSet = context.getStringAttribute("resultSet");
String foreignColumn = context.getStringAttribute("foreignColumn");
boolean lazy = "lazy".equals(context.getStringAttribute("fetchType", configuration.isLazyLoadingEnabled() ? "lazy" : "eager"));
Class<?> javaTypeClass = resolveClass(javaType);
Class<? extends TypeHandler<?>> typeHandlerClass = (Class<? extends TypeHandler<?>>) resolveClass(typeHandler);
JdbcType jdbcTypeEnum = resolveJdbcType(jdbcType);
// 构建 ResultMapping 对象
//入口2
return builderAssistant.buildResultMapping(resultType, property, column, javaTypeClass, jdbcTypeEnum, nestedSelect,
nestedResultMap, notNullColumn, columnPrefix, typeHandlerClass, flags, resultSet, foreignColumn, lazy);
}
private String processNestedResultMappings(XNode context, List<ResultMapping> resultMappings) throws Exception {
if (("association".equals(context.getName()) || "collection".equals(context.getName()) || "case".equals(context.getName())) && context.getStringAttribute("select") == null) {
ResultMap resultMap = this.resultMapElement(context, resultMappings);
return resultMap.getId();
} else {
return null;
}
}
只要此节点是（association或者collection）并且select为空,就说明是嵌套查询，那如果select不为空呢？那说明是延迟加载此节点的信息，并不属于嵌套查询，但是有可能有多个association或者collection，有一个设置为延迟加载也就是select属性不为空，有一个没有设置延迟加载，那说明resultMap中有嵌套查询的ResultMapping，也有延迟加载的ResultMapping，这个在后面结果集映射时会用到。
下面以
第一种配置方式是通过 resultMap 属性引用其他的
<resultMap id="articleResult" type="Article">
<id property="id" column="id"/>
<result property="title" column="article_title"/>
<!-- 引用 authorResult，此时为嵌套查询 -->
<association property="article_author" column="article_author_id" javaType="Author" resultMap="authorResult"/>
<!-- 引用 authorResult，此时为延迟查询 -->
<association property="article_author" column="article_author_id" javaType="Author" select="authorResult"/>
</resultMap>
<resultMap id="authorResult" type="Author">
<id property="id" column="author_id"/>
<result property="name" column="author_name"/>
</resultMap>
第二种配置方式是采取 resultMap 嵌套的方式进行配置，如下：
<resultMap id="articleResult" type="Article">
<id property="id" column="id"/>
<result property="title" column="article_title"/>
<!-- resultMap 嵌套 -->
<association property="article_author" javaType="Author">
<id property="id" column="author_id"/>
<result property="name" column="author_name"/>
</association>
</resultMap>
第二种配置，
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) {
// resultType：即 <resultMap type="xxx"/> 中的 type 属性
// property：即 <result property="xxx"/> 中的 property 属性
//入口1
Class<?> javaTypeClass = resolveResultJavaType(resultType, property, javaType);
TypeHandler<?> typeHandlerInstance = resolveTypeHandler(javaTypeClass, typeHandler);
List<ResultMapping> composites = parseCompositeColumnName(column);
// 通过建造模式构建 ResultMapping
return new ResultMapping.Builder(configuration, property, column, javaTypeClass)
.jdbcType(jdbcType)
.nestedQueryId(applyCurrentNamespace(nestedSelect, true))
.nestedResultMapId(applyCurrentNamespace(nestedResultMap, true))
.resultSet(resultSet)
.typeHandler(typeHandlerInstance)
.flags(flags == null ? new ArrayList<ResultFlag>() : flags)
.composites(composites)
.notNullColumns(parseMultipleColumnNames(notNullColumn))
.columnPrefix(columnPrefix)
.foreignColumn(foreignColumn)
.lazy(lazy)
.build();//入口2
}
private Class<?> resolveResultJavaType(Class<?> resultType, String property, Class<?> javaType) {
if (javaType == null && property != null) {
try {
//获取ResultMap中的type属性的元类，如<resultMap id="user" type="java.model.User"/> 中User的元类
MetaClass metaResultType = MetaClass.forClass(resultType, this.configuration.getReflectorFactory());
//<result property="name" javaType="String"/>,如果result中没有设置javaType，则获取元类属性对那个的类型
javaType = metaResultType.getSetterType(property);
} catch (Exception var5) {
;
}
}
if (javaType == null) {
javaType = Object.class;
}
return javaType;
}
public ResultMapping build() {
resultMapping.flags = Collections.unmodifiableList(resultMapping.flags);
resultMapping.composites = Collections.unmodifiableList(resultMapping.composites);
resolveTypeHandler();
validate();
return resultMapping;
}
public class ResultMapping {
private Configuration configuration;
private String property;
private String column;
private Class<?> javaType;
private JdbcType jdbcType;
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;
private boolean lazy;
ResultMapping() {
}
}
我们看到ResultMapping中有属性nestedResultMapId表示嵌套查询和nestedQueryId表示延迟查询
ResultMapping就是和ResultMap中子节点id和result对应
<id column="wi_id" jdbcType="INTEGER" property="id" />
<result column="warrant_no" jdbcType="String" jdbcType="CHAR" property="warrantNo" />
前面的分析我们知道了
public ResultMap resolve() {
return assistant.addResultMap(this.id, this.type, this.extend, this.discriminator, this.resultMappings, this.autoMapping);
}
public ResultMap addResultMap(
String id, Class<?> type, String extend, Discriminator discriminator,
List<ResultMapping> resultMappings, Boolean autoMapping) {
// 为 ResultMap 的 id 和 extend 属性值拼接命名空间
id = applyCurrentNamespace(id, false);
extend = applyCurrentNamespace(extend, true);
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);
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);
}
// 构建 ResultMap
ResultMap resultMap = new ResultMap.Builder(configuration, id, type, resultMappings, autoMapping)
.discriminator(discriminator)
.build();
// 将创建好的ResultMap加入configuration中
configuration.addResultMap(resultMap);
return resultMap;
}
我们先看看ResultMap
public class ResultMap {
private String id;
private Class<?> type;
private List<ResultMapping> resultMappings;
//用于存储 <id> 节点对应的 ResultMapping 对象
private List<ResultMapping> idResultMappings;
private List<ResultMapping> constructorResultMappings;
//用于存储 <id> 和 <result> 节点对应的 ResultMapping 对象
private List<ResultMapping> propertyResultMappings;
//用于存储 所有<id>、<result> 节点 column 属性
private Set<String> mappedColumns;
private Discriminator discriminator;
private boolean hasNestedResultMaps;
private boolean hasNestedQueries;
private Boolean autoMapping;
private ResultMap() {
}
//略
}
再来看看通过建造模式构建 ResultMap 实例
public ResultMap build() {
if (resultMap.id == null) {
throw new IllegalArgumentException("ResultMaps must have an id");
}
resultMap.mappedColumns = new HashSet<String>();
resultMap.mappedProperties = new HashSet<String>();
resultMap.idResultMappings = new ArrayList<ResultMapping>();
resultMap.constructorResultMappings = new ArrayList<ResultMapping>();
resultMap.propertyResultMappings = new ArrayList<ResultMapping>();
final List<String> constructorArgNames = new ArrayList<String>();
for (ResultMapping resultMapping : resultMap.resultMappings) {
/*
* resultMapping.getNestedQueryId()不为空，表示当前resultMap是中有需要延迟查询的属性
* resultMapping.getNestedResultMapId()不为空，表示当前resultMap是一个嵌套查询
* 有可能当前ResultMapp既是一个嵌套查询，又存在延迟查询的属性
*/
resultMap.hasNestedQueries = resultMap.hasNestedQueries || resultMapping.getNestedQueryId() != null;
resultMap.hasNestedResultMaps = resultMap.hasNestedResultMaps || (resultMapping.getNestedResultMapId() != null && resultMapping.getResultSet() == null);
final String column = resultMapping.getColumn();
if (column != null) {
// 将 colum 转换成大写，并添加到 mappedColumns 集合中
resultMap.mappedColumns.add(column.toUpperCase(Locale.ENGLISH));
} else if (resultMapping.isCompositeResult()) {
for (ResultMapping compositeResultMapping : resultMapping.getComposites()) {
final String compositeColumn = compositeResultMapping.getColumn();
if (compositeColumn != null) {
resultMap.mappedColumns.add(compositeColumn.toUpperCase(Locale.ENGLISH));
}
}
}
// 添加属性 property 到 mappedProperties 集合中
final String property = resultMapping.getProperty();
if (property != null) {
resultMap.mappedProperties.add(property);
}
if (resultMapping.getFlags().contains(ResultFlag.CONSTRUCTOR)) {
resultMap.constructorResultMappings.add(resultMapping);
if (resultMapping.getProperty() != null) {
constructorArgNames.add(resultMapping.getProperty());
}
} else {
// 添加 resultMapping 到 propertyResultMappings 中
resultMap.propertyResultMappings.add(resultMapping);
}
if (resultMapping.getFlags().contains(ResultFlag.ID)) {
// 添加 resultMapping 到 idResultMappings 中
resultMap.idResultMappings.add(resultMapping);
}
}
if (resultMap.idResultMappings.isEmpty()) {
resultMap.idResultMappings.addAll(resultMap.resultMappings);
}
if (!constructorArgNames.isEmpty()) {
final List<String> actualArgNames = argNamesOfMatchingConstructor(constructorArgNames);
if (actualArgNames == null) {
throw new BuilderException("Error in result map '" + resultMap.id
+ "'. Failed to find a constructor in '"
+ resultMap.getType().getName() + "' by arg names " + constructorArgNames
+ ". There might be more info in debug log.");
}
Collections.sort(resultMap.constructorResultMappings, new Comparator<ResultMapping>() {
@Override
public int compare(ResultMapping o1, ResultMapping o2) {
int paramIdx1 = actualArgNames.indexOf(o1.getProperty());
int paramIdx2 = actualArgNames.indexOf(o2.getProperty());
return paramIdx1 - paramIdx2;
}
});
}
// 将以下这些集合变为不可修改集合
resultMap.resultMappings = Collections.unmodifiableList(resultMap.resultMappings);
resultMap.idResultMappings = Collections.unmodifiableList(resultMap.idResultMappings);
resultMap.constructorResultMappings = Collections.unmodifiableList(resultMap.constructorResultMappings);
resultMap.propertyResultMappings = Collections.unmodifiableList(resultMap.propertyResultMappings);
resultMap.mappedColumns = Collections.unmodifiableSet(resultMap.mappedColumns);
return resultMap;
}
主要做的事情就是将 ResultMapping 实例及属性分别存储到不同的集合中。
解析 sql 节点
<sql id="table">
user
</sql>
<select id="findOne" resultType="Article">
SELECT * FROM <include refid="table"/> WHERE id = #{id}
</select>
private void sqlElement(List<XNode> list) throws Exception {
if (configuration.getDatabaseId() != null) {
// 调用 sqlElement 解析 <sql> 节点
sqlElement(list, configuration.getDatabaseId());
}
// 再次调用 sqlElement，不同的是，这次调用，该方法的第二个参数为 null
sqlElement(list, null);
}
private void sqlElement(List<XNode> list, String requiredDatabaseId) throws Exception {
for (XNode context : list) {
// 获取 id 和 databaseId 属性
String databaseId = context.getStringAttribute("databaseId");
String id = context.getStringAttribute("id");
// id = currentNamespace + "." + id
id = builderAssistant.applyCurrentNamespace(id, false);
// 检测当前 databaseId 和 requiredDatabaseId 是否一致
if (databaseIdMatchesCurrent(id, databaseId, requiredDatabaseId)) {
// 将 <id, XNode> 键值对缓存到XMLMapperBuilder对象的 sqlFragments 属性中，以供后面的sql语句使用
sqlFragments.put(id, context);
}
}
}
解析select|insert|update|delete节点
private void buildStatementFromContext(List<XNode> list) {
if (configuration.getDatabaseId() != null) {
// 调用重载方法构建 Statement
buildStatementFromContext(list, configuration.getDatabaseId());
}
buildStatementFromContext(list, null);
}
private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
for (XNode context : list) {
// 创建 XMLStatementBuilder 建造类
final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
try {
/*
* 解析sql节点，将其封装到 Statement 对象中，并将解析结果存储到 configuration 的 mappedStatements 集合中
*/
statementParser.parseStatementNode();
} catch (IncompleteElementException e) {
configuration.addIncompleteStatement(statementParser);
}
}
}
statementParser.parseStatementNode()：
public void parseStatementNode() {
// 获取 id 和 databaseId 属性
String id = context.getStringAttribute("id");
String databaseId = context.getStringAttribute("databaseId");
if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
return;
}
// 获取各种属性
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);
// 通过别名解析 resultType 对应的类型
Class<?> resultTypeClass = resolveClass(resultType);
String resultSetType = context.getStringAttribute("resultSetType");
// 解析 Statement 类型，默认为 PREPARED
StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
// 解析 ResultSetType
ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
// 获取节点的名称，比如 <select> 节点名称为 select
String nodeName = context.getNode().getNodeName();
// 根据节点名称解析 SqlCommandType
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);
// 解析 <include> 节点
XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
includeParser.applyIncludes(context.getNode());
processSelectKeyNodes(id, parameterTypeClass, langDriver);
// 解析 SQL 语句
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)) ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
}
/*
* 构建 MappedStatement 对象，并将该对象存储到 Configuration 的 mappedStatements 集合中
*/
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}
我们主要来分析下面几个重要的方法：
解析
解析 SQL，获取 SqlSource
构建 MappedStatement 实例
解析
<mapper namespace="java.mybaits.dao.UserMapper">
<sql id="table">
user
</sql>
<select id="findOne" resultType="User">
SELECT * FROM <include refid="table"/> WHERE id = #{id}
</select>
</mapper>
public void applyIncludes(Node source) {
Properties variablesContext = new Properties();
Properties configurationVariables = configuration.getVariables();
if (configurationVariables != null) {
// 将 configurationVariables 中的数据添加到 variablesContext 中
variablesContext.putAll(configurationVariables);
}
// 调用重载方法处理 <include> 节点
applyIncludes(source, variablesContext, false);
}
private void applyIncludes(Node source, final Properties variablesContext, boolean included) {
// 第一个条件分支
if (source.getNodeName().equals("include")) {
//获取 <sql> 节点。
Node toInclude = findSqlFragment(getStringAttribute(source, "refid"), variablesContext);
Properties toIncludeContext = getVariablesContext(source, variablesContext);
applyIncludes(toInclude, toIncludeContext, true);
if (toInclude.getOwnerDocument() != source.getOwnerDocument()) {
toInclude = source.getOwnerDocument().importNode(toInclude, true);
}
// 将 <select>节点中的 <include> 节点替换为 <sql> 节点
source.getParentNode().replaceChild(toInclude, source);
while (toInclude.hasChildNodes()) {
// 将 <sql> 中的内容插入到 <sql> 节点之前
toInclude.getParentNode().insertBefore(toInclude.getFirstChild(), toInclude);
}
/*
* 前面已经将 <sql> 节点的内容插入到 dom 中了，
* 现在不需要 <sql> 节点了，这里将该节点从 dom 中移除
*/
toInclude.getParentNode().removeChild(toInclude);
// 第二个条件分支
} else if (source.getNodeType() == Node.ELEMENT_NODE) {
if (included && !variablesContext.isEmpty()) {
NamedNodeMap attributes = source.getAttributes();
for (int i = 0; i < attributes.getLength(); i++) {
Node attr = attributes.item(i);
// 将 source 节点属性中的占位符 ${} 替换成具体的属性值
attr.setNodeValue(PropertyParser.parse(attr.getNodeValue(), variablesContext));
}
}
NodeList children = source.getChildNodes();
for (int i = 0; i < children.getLength(); i++) {
// 递归调用
applyIncludes(children.item(i), variablesContext, included);
}
// 第三个条件分支
} else if (included && source.getNodeType() == Node.TEXT_NODE && !variablesContext.isEmpty()) {
// 将文本（text）节点中的属性占位符 ${} 替换成具体的属性值
source.setNodeValue(PropertyParser.parse(source.getNodeValue(), variablesContext));
}
}
我们先来看一下 applyIncludes 方法第一次被调用时的状态，source为
接下来要做的事情是遍历列表，然后将子节点作为参数进行递归调用。第一个子节点调用applyIncludes方法，source为 SELECT * FROM 节点，节点类型：TEXT_NODE，进入分支三，没有${}，不会替换，则节点一结束返回，什么都没有做。第二个节点调用applyIncludes方法，此时source为
创建SqlSource
创建SqlSource在createSqlSource方法中
public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) {
XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType);
return builder.parseScriptNode();
}
// -☆- XMLScriptBuilder
public SqlSource parseScriptNode() {
// 解析 SQL 语句节点
MixedSqlNode rootSqlNode = parseDynamicTags(context);
SqlSource sqlSource = null;
// 根据 isDynamic 状态创建不同的 SqlSource
if (isDynamic) {
sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
} else {
sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);
}
return sqlSource;
}
/** 该方法用于初始化 nodeHandlerMap 集合，该集合后面会用到 */
private void initNodeHandlerMap() {
nodeHandlerMap.put("trim", new TrimHandler());
nodeHandlerMap.put("where", new WhereHandler());
nodeHandlerMap.put("set", new SetHandler());
nodeHandlerMap.put("foreach", new ForEachHandler());
nodeHandlerMap.put("if", new IfHandler());
nodeHandlerMap.put("choose", new ChooseHandler());
nodeHandlerMap.put("when", new IfHandler());
nodeHandlerMap.put("otherwise", new OtherwiseHandler());
nodeHandlerMap.put("bind", new BindHandler());
}
protected MixedSqlNode parseDynamicTags(XNode node) {
List<SqlNode> contents = new ArrayList<SqlNode>();
NodeList children = node.getNode().getChildNodes();
// 遍历子节点
for (int i = 0; i < children.getLength(); i++) {
XNode child = node.newXNode(children.item(i));
//如果节点是TEXT_NODE类型
if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE || child.getNode().getNodeType() == Node.TEXT_NODE) {
// 获取文本内容
String data = child.getStringBody("");
TextSqlNode textSqlNode = new TextSqlNode(data);
// 若文本中包含 ${} 占位符，会被认为是动态节点
if (textSqlNode.isDynamic()) {
contents.add(textSqlNode);
// 设置 isDynamic 为 true
isDynamic = true;
} else {
// 创建 StaticTextSqlNode
contents.add(new StaticTextSqlNode(data));
}
// child 节点是 ELEMENT_NODE 类型，比如 <if>、<where> 等
} else if (child.getNode().getNodeType() == Node.ELEMENT_NODE) {
// 获取节点名称，比如 if、where、trim 等
String nodeName = child.getNode().getNodeName();
// 根据节点名称获取 NodeHandler，也就是上面注册的nodeHandlerMap
NodeHandler handler = nodeHandlerMap.get(nodeName);
if (handler == null) {
throw new BuilderException("Unknown element <" + nodeName + "> in SQL statement.");
}
// 处理 child 节点，生成相应的 SqlNode
handler.handleNode(child, contents);
// 设置 isDynamic 为 true
isDynamic = true;
}
}
return new MixedSqlNode(contents);
}
对于if、trim、where等这些动态节点，是通过对应的handler来解析的，如下
handler.handleNode(child, contents);
该代码用于处理动态 SQL 节点，并生成相应的 SqlNode。下面来简单分析一下 WhereHandler 的代码。
/** 定义在 XMLScriptBuilder 中 */
private class WhereHandler implements NodeHandler {
public WhereHandler() {
}
@Override
public void handleNode(XNode nodeToHandle, List<SqlNode> targetContents) {
// 调用 parseDynamicTags 解析 <where> 节点
MixedSqlNode mixedSqlNode = parseDynamicTags(nodeToHandle);
// 创建 WhereSqlNode
WhereSqlNode where = new WhereSqlNode(configuration, mixedSqlNode);
// 添加到 targetContents
targetContents.add(where);
}
}
我们已经将 XML 配置解析了 SqlSource，下面我们看看MappedStatement的构建。
构建MappedStatement
SQL 语句节点可以定义很多属性，这些属性和属性值最终存储在 MappedStatement 中。
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");
}
// 拼接上命名空间，如 <select id="findOne" resultType="User">，则id=java.mybaits.dao.UserMapper.findOne
id = applyCurrentNamespace(id, false);
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
// 创建建造器，设置各种属性
MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType)
.resource(resource).fetchSize(fetchSize).timeout(timeout)
.statementType(statementType).keyGenerator(keyGenerator)
.keyProperty(keyProperty).keyColumn(keyColumn).databaseId(databaseId)
.lang(lang).resultOrdered(resultOrdered).resultSets(resultSets)
.resultMaps(getStatementResultMaps(resultMap, resultType, id))
.flushCacheRequired(valueOrDefault(flushCache, !isSelect))
.resultSetType(resultSetType).useCache(valueOrDefault(useCache, isSelect))
.cache(currentCache);//这里用到了前面解析<cache>节点时创建的Cache对象，设置到MappedStatement对象里面的cache属性中
// 获取或创建 ParameterMap
ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);
if (statementParameterMap != null) {
statementBuilder.parameterMap(statementParameterMap);
}
// 构建 MappedStatement
MappedStatement statement = statementBuilder.build();
// 添加 MappedStatement 到 configuration 的 mappedStatements 集合中
// 通过UserMapper代理对象调用findOne方法时，就可以拼接UserMapper接口名java.mybaits.dao.UserMapper和findOne方法找到id=java.mybaits.dao.UserMapper的MappedStatement，然后执行对应的sql语句
configuration.addMappedStatement(statement);
return statement;
}
这里我们要注意，MappedStatement对象中有一个cache属性，将前面解析
我们还要注意一个地方，.resultMaps(getStatementResultMaps(resultMap, resultType, id))，设置MappedStatement的resultMaps，我们来看看是怎么获取resultMap的
private List<ResultMap> getStatementResultMaps(String resultMap, Class<?> resultType, String statementId) {
//拼接上当前nameSpace
resultMap = this.applyCurrentNamespace(resultMap, true);
//创建一个集合
List<ResultMap> resultMaps = new ArrayList();
if (resultMap != null) {
//通过,分隔字符串，一般resultMap只会是一个，不会使用逗号
String[] resultMapNames = resultMap.split(",");
String[] arr$ = resultMapNames;
int len$ = resultMapNames.length;
for(int i$ = 0; i$ < len$; ++i$) {
String resultMapName = arr$[i$];
try {
//从configuration中通过resultMapName获取ResultMap对象加入到resultMaps中
resultMaps.add(this.configuration.getResultMap(resultMapName.trim()));
} catch (IllegalArgumentException var11) {
throw new IncompleteElementException("Could not find result map " + resultMapName, var11);
}
}
} else if (resultType != null) {
ResultMap inlineResultMap = (new org.apache.ibatis.mapping.ResultMap.Builder(this.configuration, statementId + "-Inline", resultType, new ArrayList(), (Boolean)null)).build();
resultMaps.add(inlineResultMap);
}
return resultMaps;
}
从configuration中获取到ResultMap并设置到MappedStatement中，当查询结束后，就可以拿到ResultMap进行结果映射，这个在后面讲
Mapper 接口绑定
映射文件解析完成后，我们需要通过命名空间将绑定 mapper 接口，看看具体绑定的啥
private void bindMapperForNamespace() {
// 获取映射文件的命名空间
String namespace = builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class<?> boundType = null;
try {
// 根据命名空间解析 mapper 类型
boundType = Resources.classForName(namespace);
} catch (ClassNotFoundException e) {
}
if (boundType != null) {
// 检测当前 mapper 类是否被绑定过
if (!configuration.hasMapper(boundType)) {
configuration.addLoadedResource("namespace:" + namespace);
// 绑定 mapper 类
configuration.addMapper(boundType);
}
}
}
}
// Configuration
public
// 通过 MapperRegistry 绑定 mapper 类
mapperRegistry.addMapper(type);
}
// MapperRegistry
public
if (type.isInterface()) {
if (hasMapper(type)) {
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
/*
* 将 type 和 MapperProxyFactory 进行绑定，MapperProxyFactory 可为 mapper 接口生成代理类
*/
knownMappers.put(type, new MapperProxyFactory
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
// 解析注解中的信息
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
其实就是获取当前映射文件的命名空间，并获取其Class，也就是获取每个Mapper接口，然后为每个Mapper接口创建一个代理类工厂，new MapperProxyFactory
public class MapperProxyFactory<T> {
//存放Mapper接口Class
private final Class<T> mapperInterface;
private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap();
public MapperProxyFactory(Class<T> mapperInterface) {
this.mapperInterface = mapperInterface;
}
public Class<T> getMapperInterface() {
return this.mapperInterface;
}
public Map<Method, MapperMethod> getMethodCache() {
return this.methodCache;
}
protected T newInstance(MapperProxy<T> mapperProxy) {
//生成mapperInterface的代理类
return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
return this.newInstance(mapperProxy);
}
}