经过上一篇的getMapper方法的讲解之后getMapper解析。
此时Mybatis已经通过动态代理,创建了Dao的具体对象。因为其中MapperProxy实现了InvocationHandler,所以在执行具体的方法时,会执行MapperProxy中的invoke方法。
test方法
前几篇文章中已经解析到了getMapper方法,所以本篇会针对具体方法继续向下进行解析。
public void test02() {// 根据全局配置文件创建出SqlSessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = null;try {//加载mybatis-config.xml并转换为Stream流inputStream = Resources.getResourceAsStream(resource);} catch (IOException e) {e.printStackTrace();}// SqlSessionFactory:负责创建SqlSession对象的工厂SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);// SqlSession:表示跟数据库建议的一次会话// 获取数据库的会话,创建出数据库连接的会话对象(事务工厂,事务对象,执行器,如果有插件的话会进行插件的解析)SqlSession sqlSession = sqlSessionFactory.openSession();Emp empByEmpno = null;try {// 获取要调用的接口类,创建出对应的mapper的动态代理对象(mapperRegistry.knownMapper)EmpDao mapper = sqlSession.getMapper(EmpDao.class);// 调用方法开始执行empByEmpno = mapper.findEmpByEmpnoAndEname(7369, "SMITH");} catch (Exception e) {e.printStackTrace();} finally {sqlSession.close();}System.out.println(empByEmpno);}
invoke
前面已经提到,因为MapperProxy实现了InvocationHandler,所以在执行具体的方法时,会执行MapperProxy中的invoke方法。
public class MapperProxy<T> implements InvocationHandler, Serializable {private static final long serialVersionUID = -4724728412955527868L;private static final int ALLOWED_MODES = MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED| MethodHandles.Lookup.PACKAGE | MethodHandles.Lookup.PUBLIC;private static final Constructor<Lookup> lookupConstructor;private static final Method privateLookupInMethod;private final SqlSession sqlSession;private final Class<T> mapperInterface;//用于缓存MapperMethod对象(其中属性包含SqlCommand和MethodSignature),其中key是mapper接口中方法对应的Method对象,value是MapperMethod对象//MapperMethod对象会完成参数转换,以及SQL语句的执行功能,需要注意的是,MapperMethod中并不记录任何状态相关的信息,所以可以在多个代理对象之间共享private final Map<Method, MapperMethodInvoker> methodCache;@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {//如果目标方法继承自Object,则直接调用该方法if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);} else {//根据被调用接口方法的method对象,从缓存中获取MapperMethodInvoker对象,如果没有则创建一个并放入缓存,执行invoke方法。return cachedInvoker(method).invoke(proxy, method, args, sqlSession);}} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}}
}
// 省略部分代码。。。。
cachedInvoker
因为是普通的接口方法,所以会执行cachedInvoker方法,将method放入methodCache缓存中。
private MapperMethodInvoker cachedInvoker(Method method) throws Throwable {try {//如果能够在methodCache(Map<Method, MapperMethodInvoker>)中,根据method(key)找到value,则返回,找不到,就加到methodCache中//会执行ConcurrentHashMap的computeIfAbsent方法 ->// MapperProxyFactory加载时private final Map<Method, MapperMethodInvoker> methodCache = new ConcurrentHashMap<>();return MapUtil.computeIfAbsent(methodCache, method, m -> {//因为JDK1.8新特性,允许接口中有方法的具体实现(default修饰),所以在此处做判断,看要执行的方法是否是接口中的实现方法。//如果是接口中的实现方法会走下面的逻辑if (m.isDefault()) {try {if (privateLookupInMethod == null) {//根据JDK8和JDK9做了不同的操作return new DefaultMethodInvoker(getMethodHandleJava8(method));} else {return new DefaultMethodInvoker(getMethodHandleJava9(method));}} catch (IllegalAccessException | InstantiationException | InvocationTargetException| NoSuchMethodException e) {throw new RuntimeException(e);}} else {//普通的接口方法return new PlainMethodInvoker(new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));}});} catch (RuntimeException re) {Throwable cause = re.getCause();throw cause == null ? re : cause;}}
MapperMethod
如果是普通的接口方法,则先会根据mapperInterface, method和Configuration构建MapperMethod。
包含了要执行的具体sql,方法参数、返回值等。。。
public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {this.command = new SqlCommand(config, mapperInterface, method);this.method = new MethodSignature(config, mapperInterface, method);}
SqlCommand
构造sqlCommand,根据接口名+方法名,获取MapperStatement对象,
public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {//获取方法名final String methodName = method.getName();//Dao接口对象final Class<?> declaringClass = method.getDeclaringClass();MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,configuration);//处理Flush注解if (ms == null) {if (method.getAnnotation(Flush.class) != null) {name = null;type = SqlCommandType.FLUSH;} else {throw new BindingException("Invalid bound statement (not found): "+ mapperInterface.getName() + "." + methodName);}} else {//接口全限定名+方法名name = ms.getId();//操作类型 select、insert、update。。。type = ms.getSqlCommandType();//如果type是unknown类型,抛异常if (type == SqlCommandType.UNKNOWN) {throw new BindingException("Unknown execution method for: " + name);}}}
resolveMappedStatement
private MappedStatement resolveMappedStatement(Class<?> mapperInterface, String methodName,Class<?> declaringClass, Configuration configuration) {//接口名+方法名拼接的idString statementId = mapperInterface.getName() + "." + methodName;//因为之前解析时,MapperStatement中解析了mapper.xml所有属性节点。//configuration中的MapperStatement中是否包含当前的接口名+方法名。//所以,要想执行具体的SQL语句,就要根据statementId获取到mapperStatement对象if (configuration.hasStatement(statementId)) {return configuration.getMappedStatement(statementId);} else if (mapperInterface.equals(declaringClass)) {return null;}for (Class<?> superInterface : mapperInterface.getInterfaces()) {if (declaringClass.isAssignableFrom(superInterface)) {MappedStatement ms = resolveMappedStatement(superInterface, methodName,declaringClass, configuration);if (ms != null) {return ms;}}}return null;}
MethodSignature
类名可以翻译为方法签名,获取返回类型
public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {//解析方法返回值类型Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);if (resolvedReturnType instanceof Class<?>) {this.returnType = (Class<?>) resolvedReturnType;} else if (resolvedReturnType instanceof ParameterizedType) {this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();} else {this.returnType = method.getReturnType();}//根据返回类型初始化returnsVoid、returnsMany、returnsCursor、returnsOptional等参数this.returnsVoid = void.class.equals(this.returnType);this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray();this.returnsCursor = Cursor.class.equals(this.returnType);this.returnsOptional = Optional.class.equals(this.returnType);// 若MethodSignature对应方法的返回值是Map且制定了@MapKey注解,则使用getMapKey方法处理this.mapKey = getMapKey(method);this.returnsMap = this.mapKey != null;// 初始化rowBoundsIndex、resultHandlerIndex字段this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);// 创建ParamNameResolver对象this.paramNameResolver = new ParamNameResolver(configuration, method);}
ParamNameResolver
参数解析、映射
public ParamNameResolver(Configuration config, Method method) {this.useActualParamName = config.isUseActualParamName();//获取参数列表中每个参数的类型final Class<?>[] paramTypes = method.getParameterTypes();//获取到注解final Annotation[][] paramAnnotations = method.getParameterAnnotations();//记录参数索引和参数名的对应关系final SortedMap<Integer, String> map = new TreeMap<>();int paramCount = paramAnnotations.length;//遍历所有注解for (int paramIndex = 0; paramIndex < paramCount; paramIndex++) {//if (isSpecialParameter(paramTypes[paramIndex])) {// skip special parameters// 如果参数是RowBounds类型或ResultHandler类型,则跳过对该参数的分析continue;}String name = null;//遍历注解for (Annotation annotation : paramAnnotations[paramIndex]) {if (annotation instanceof Param) {hasParamAnnotation = true;// 获取@Param注解指定的参数名称name = ((Param) annotation).value();break;}}if (name == null) {// @Param was not specified.// 该参数没有对应的@Param注解,则根据配置决定是否使用参数实际名称作为其名称if (useActualParamName) {name = getActualParamName(method, paramIndex);}if (name == null) {// use the parameter index as the name ("0", "1", ...)// gcode issue #71// 使用参数的索引作为其名称 arg0,arg1name = String.valueOf(map.size());}}// 记录到map中保存map.put(paramIndex, name);}// 初始化name集合names = Collections.unmodifiableSortedMap(map);}
再次回到cachedInvoker方法,因为第一次进来methodCache(Map<Method, MapperMethodInvoker>)中为该method的key为null,所以会执行上面的操作,当上面的操作执行完后,methodCache中就已经有Method的键值对了。而后,会执行MapperProxy中的invoke方法,来执行SQL的查询。
MapperProxy
public class MapperProxy<T> implements InvocationHandler, Serializable {private static class PlainMethodInvoker implements MapperMethodInvoker {private final MapperMethod mapperMethod;public PlainMethodInvoker(MapperMethod mapperMethod) {super();this.mapperMethod = mapperMethod;}//省略部分代码。。。。@Overridepublic Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable {return mapperMethod.execute(sqlSession, args);}}}
execute
根据SQL的命令类型,来执行具体的查询
public Object execute(SqlSession sqlSession, Object[] args) {Object result;//获取到SQL的操作类型switch (command.getType()) {case INSERT: {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.insert(command.getName(), param));break;}case UPDATE: {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.update(command.getName(), param));break;}case DELETE: {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.delete(command.getName(), param));break;}case SELECT://处理返回值是Void并且ResultSet通过ResultHandler处理的方法if (method.returnsVoid() && method.hasResultHandler()) {//如果有结果处理器(ResultHandler)executeWithResultHandler(sqlSession, args);result = null;//是否返回多条记录} else if (method.returnsMany()) {result = executeForMany(sqlSession, args);//是否返回Map类型} else if (method.returnsMap()) {result = executeForMap(sqlSession, args);//返回cursor} else if (method.returnsCursor()) {result = executeForCursor(sqlSession, args);//返回单一对象的处理办法} else {//得到实参和参数名的映射Object param = method.convertArgsToSqlCommandParam(args);result = sqlSession.selectOne(command.getName(), param);if (method.returnsOptional()&& (result == null || !method.getReturnType().equals(result.getClass()))) {result = Optional.ofNullable(result);}}break;case FLUSH:result = sqlSession.flushStatements();break;default:throw new BindingException("Unknown execution method for: " + command.getName());}if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {throw new BindingException("Mapper method '" + command.getName()+ " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");}return result;}
convertArgsToSqlCommandParam
获取到实参,并进行map映射
public Object convertArgsToSqlCommandParam(Object[] args) {return paramNameResolver.getNamedParams(args);}
public Object getNamedParams(Object[] args) {final int paramCount = names.size();//没有参数,返回nullif (args == null || paramCount == 0) {return null;//没使用Param注解且只有一个参数} else if (!hasParamAnnotation && paramCount == 1) {Object value = args[names.firstKey()];return wrapToMapIfCollection(value, useActualParamName ? names.get(0) : null);} else {//处理使用@Param注解指定了参数名称或者多个参数final Map<String, Object> param = new ParamMap<>();int i = 0;//names是索引为key,参数名称为value的Map结构for (Map.Entry<Integer, String> entry : names.entrySet()) {//ParamMap记录了参数名称和实际参数的关系,继承了HashMap,不允许Key相同。param.put(entry.getValue(), args[entry.getKey()]);//生成param1、param2的参数形式final String genericParamName = GENERIC_NAME_PREFIX + (i + 1);// 如果names的map中,key也是以param1方式命名,则不添加,否则将param1的形式也添加到paramMap中if (!names.containsValue(genericParamName)) {param.put(genericParamName, args[entry.getKey()]);}i++;}return param;}}
selectOne
针对返回单一数据的查询
@Overridepublic <T> T selectOne(String statement, Object parameter) {// 还是调用selectList方法List<T> list = this.selectList(statement, parameter);//返回list0if (list.size() == 1) {return list.get(0);} else if (list.size() > 1) {throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());} else {//没有则返回nullreturn null;}}public <E> List<E> selectList(String statement, Object parameter) {//RowBounds.DEFAULT使用默认分页return this.selectList(statement, parameter, RowBounds.DEFAULT);}
selectList
private <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {try {//从Configuration中获取MappedStatement,包含sql语句MappedStatement ms = configuration.getMappedStatement(statement);//使用执行器来查询结果,handler是个null//wrapCollection(parameter)获取到参数return executor.query(ms, wrapCollection(parameter), rowBounds, handler);} catch (Exception e) {throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);} finally {ErrorContext.instance().reset();}}
query
执行具体查询
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {//获取BoundSql对象,里面包含SQL、形参和实参BoundSql boundSql = ms.getBoundSql(parameterObject);//创建CacheKeyCacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);}
createCacheKey
根据id、偏移量、limit等设置cacheKey
public CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) {//Executor,默认SIMPLE,根据delegate创建缓存对象return delegate.createCacheKey(ms, parameterObject, rowBounds, boundSql);}public CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) {//看当前Executor是否关闭if (closed) {throw new ExecutorException("Executor was closed.");}CacheKey cacheKey = new CacheKey();//将msId添加进cacheKey中 -> 接口全限定名+方法名cacheKey.update(ms.getId());cacheKey.update(rowBounds.getOffset());//将limit放到cacheKey中cacheKey.update(rowBounds.getLimit());//将sql放到cacheKey中cacheKey.update(boundSql.getSql());List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();TypeHandlerRegistry typeHandlerRegistry = ms.getConfiguration().getTypeHandlerRegistry();// mimic DefaultParameterHandler logic//获取传入的实参,放到cacheKey中for (ParameterMapping parameterMapping : parameterMappings) {if (parameterMapping.getMode() != ParameterMode.OUT) {Object value;String propertyName = parameterMapping.getProperty();if (boundSql.hasAdditionalParameter(propertyName)) {value = boundSql.getAdditionalParameter(propertyName);} else if (parameterObject == null) {value = null;} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {value = parameterObject;} else {MetaObject metaObject = configuration.newMetaObject(parameterObject);value = metaObject.getValue(propertyName);}//将实参添加到cacheKey中cacheKey.update(value);}}if (configuration.getEnvironment() != null) {// issue #176cacheKey.update(configuration.getEnvironment().getId());}return cacheKey;}
query
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());//看缓存是否关闭if (closed) {throw new ExecutorException("Executor was closed.");}//queryStack 查询栈if (queryStack == 0 && ms.isFlushCacheRequired()) {//嵌套查询,并且select节点配置的flushCache属性为true时,才会清空一级缓存,flushCache配置项是影响一级缓存中结果对象存活时长的第一个方面clearLocalCache();}List<E> list;try {//栈++queryStack++;//查询一级缓存,key为cacheKeylist = resultHandler == null ? (List<E>) localCache.getObject(key) : null;if (list != null) {handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);} else {//一级缓存为null,从数据库中查询list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);}} finally {queryStack--;}if (queryStack == 0) {for (DeferredLoad deferredLoad : deferredLoads) {deferredLoad.load();}// issue #601deferredLoads.clear();if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {// issue #482clearLocalCache();}}return list;}
queryFromDatabase
一级缓存为null,从数据库查询
// 从数据库查private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {List<E> list;// 在缓存中添加占位符localCache.putObject(key, EXECUTION_PLACEHOLDER);try {// 完成数据库查询操作,并返回结果对象list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);} finally {// 删除占位符localCache.removeObject(key);}// 将真正的结果对象添加到一级缓存中localCache.putObject(key, list);// 是否未存储过程调用if (ms.getStatementType() == StatementType.CALLABLE) {// 缓存输出类型的参数localOutputParameterCache.putObject(key, parameter);}return list;}
doQuery
获取Statement对象,创建StatementHandler,调用handler执行查询
@Overridepublic <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {Statement stmt = null;try {// 获取配置对象Configuration configuration = ms.getConfiguration();// 创建StatementHandler对象,实际返回的是RoutingStatementHandler对象StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);// 完成Statement的创建和初始化stmt = prepareStatement(handler, ms.getStatementLog());// 调用query方法执行sql语句,并通过ResultSetHandler完成结果集的映射return handler.query(stmt, resultHandler);} finally {// 关闭Statement对象closeStatement(stmt);}}public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {// 获取SQL语句String sql = boundSql.getSql();// 执行SQL语句statement.execute(sql);// 映射结果集return resultSetHandler.handleResultSets(statement);}
handleResultSets
将查询后返回的结果集做映射处理
public List<Object> handleResultSets(Statement stmt) throws SQLException {ErrorContext.instance().activity("handling results").object(mappedStatement.getId());// 该集合用于保存映射结果得到的结果对象final List<Object> multipleResults = new ArrayList<>();int resultSetCount = 0;// 获取第一个ResultSet对象ResultSetWrapper rsw = getFirstResultSet(stmt);// 获取MappedStatement.resultMaps集合List<ResultMap> resultMaps = mappedStatement.getResultMaps();int resultMapCount = resultMaps.size();// 如果集合集不为空,则resultMaps集合不能为空,否则抛出异常validateResultMapsCount(rsw, resultMapCount);// 遍历resultMaps集合while (rsw != null && resultMapCount > resultSetCount) {// 获取该结果集对应的ResultMap对象ResultMap resultMap = resultMaps.get(resultSetCount);// 根据ResultMap中定义的映射规则对ResultSet进行映射,并将映射的结果对象添加到multipleResult集合中保存handleResultSet(rsw, resultMap, multipleResults, null);// 获取下一个结果集rsw = getNextResultSet(stmt);// 清空nestedResultObjects集合cleanUpAfterHandlingResultSet();// 递增resultSetCountresultSetCount++;}// 获取MappedStatement.resultSets属性,该属性对多结果集的情况使用,该属性将列出语句执行后返回的结果集,并给每个结果集一个名称,名称是逗号分隔的,String[] resultSets = mappedStatement.getResultSets();if (resultSets != null) {while (rsw != null && resultSetCount < resultSets.length) {// 根据resultSet的名称,获取未处理的ResultMappingResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);if (parentMapping != null) {String nestedResultMapId = parentMapping.getNestedResultMapId();ResultMap resultMap = configuration.getResultMap(nestedResultMapId);// 根据ResultMap对象映射结果集handleResultSet(rsw, resultMap, null, parentMapping);}// 获取下一个结果集rsw = getNextResultSet(stmt);// 清空nestedResultObjects集合cleanUpAfterHandlingResultSet();// 递增resultSetCountresultSetCount++;}}return collapseSingleResultList(multipleResults);}