Mybatis源码解析之查询流程

阅读须知

Mybatis源码版本：3.4.4

注释规则：

//单行注释做普通注释

/**/多行注释做深入分析

建议配合Mybatis源码阅读

正文

上篇文章中我们分析mapper的创建，Mybatis用JDK动态代理为mapper创建代理类，其中MapperProxy作为InvocationHandler角色，所以调用目标mapper方法时会执行其invoke方法，我们来分析MapperProxy的invoke方法：

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
//如果是从Object继承的方法，直接执行
return method.invoke(this, args);
//判断是否是默认方法，默认方法是Java8的新特性，判断逻辑与Java8 Method类的isDefault方法一样
} else if (isDefaultMethod(method)) {
//调用默认方法，这里面用到了Java7的API，有兴趣的读者可以自行了解
return invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
/*构建并缓存MapperMethod*/
final MapperMethod mapperMethod = cachedMapperMethod(method);
/*执行*/
return mapperMethod.execute(sqlSession, args);
}

MapperProxy：

private MapperMethod cachedMapperMethod(Method method) {
MapperMethod mapperMethod = methodCache.get(method);
if (mapperMethod == null) {
/*构造MapperMethod*/
mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
methodCache.put(method, mapperMethod);
}
return mapperMethod;
}

MapperMethod：

public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
/*构造sql命令对象*/
this.command = new SqlCommand(config, mapperInterface, method);
/*构造方法签名对象*/
this.method = new MethodSignature(config, mapperInterface, method);
}

MapperMethod.SqlCommand：

public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
final String methodName = method.getName();
final Class<?> declaringClass = method.getDeclaringClass();
/*解析获取MappedStatement*/
MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,
configuration);
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 {
//将MappedStatement的相关属性复制给当前对象的相关属性
name = ms.getId();
type = ms.getSqlCommandType();
if (type == SqlCommandType.UNKNOWN) {
throw new BindingException("Unknown execution method for: " + name);
}
}
}

MapperMethod.SqlCommand：

private MappedStatement resolveMappedStatement(Class<?> mapperInterface, String methodName,
Class<?> declaringClass, Configuration configuration) {
//拼接statementId
String statementId = mapperInterface.getName() + "." + methodName;
if (configuration.hasStatement(statementId)) {
//如果configuration对象中包含相应MappedStatement对象，直接返回
return configuration.getMappedStatement(statementId);
} else if (mapperInterface.equals(declaringClass)) {
//如果方法所属Class与mapper接口Class是相同的，直接返回null
return null;
}
for (Class<?> superInterface : mapperInterface.getInterfaces()) {
//遍历mapper接口类的父接口，如果与方法所属Class相同或者是其子接口，递归获取MappedStatement对象
if (declaringClass.isAssignableFrom(superInterface)) {
MappedStatement ms = resolveMappedStatement(superInterface, methodName,
declaringClass, configuration);
if (ms != null) {
return ms;
}
}
}
return null;
}

MapperMethod.MethodSignature：

public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
/*解析返回值类型*/
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();
}
//声明返回值是否是void类型
this.returnsVoid = void.class.equals(this.returnType);
//声明返回值是否是集合或者数组这种多值类型
this.returnsMany = (configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray());
this.returnsCursor = Cursor.class.equals(this.returnType);
//如果方法返回值是Map类型则判断方法上是否注解了@MapKey并获取其value属性值返回
this.mapKey = getMapKey(method);
this.returnsMap = (this.mapKey != null);
//如果方法参数中包含RowBounds类型或其子类型的参数，找出这个参数在方法参数列表中的下标值
this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
//如果方法参数中包含ResultHandler类型或其子类型的参数，找出这个参数在方法参数列表中的下标值
this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
/*声明参数名称解析器*/
this.paramNameResolver = new ParamNameResolver(configuration, method);
}

TypeParameterResolver：

public static Type resolveReturnType(Method method, Type srcType) {
Type returnType = method.getGenericReturnType();
Class<?> declaringClass = method.getDeclaringClass();
/*解析类型*/
return resolveType(returnType, srcType, declaringClass);
}

TypeParameterResolver：

private static Type resolveType(Type type, Type srcType, Class<?> declaringClass) {
if (type instanceof TypeVariable) {
//解析泛型的类型变量，TypeVariable可以获取到声明的泛型的名称、声明此泛型的类型、泛型的上下限信息等
return resolveTypeVar((TypeVariable<?>) type, srcType, declaringClass);
} else if (type instanceof ParameterizedType) {
//解析泛型的类型信息，ParameterizedType可以获取到声明的泛型的类型信息
return resolveParameterizedType((ParameterizedType) type, srcType, declaringClass);
} else if (type instanceof GenericArrayType) {
//解析数组类型的泛型信息
return resolveGenericArrayType((GenericArrayType) type, srcType, declaringClass);
} else {
return type;
}
}

关于上面出现的这几种Type类型的说明，可以参见文末的参考链接。

ParamNameResolver：

public ParamNameResolver(Configuration config, Method method) {
final Class<?>[] paramTypes = method.getParameterTypes(); //方法参数列表
final Annotation[][] paramAnnotations = method.getParameterAnnotations(); //参数的注解信息
final SortedMap<Integer, String> map = new TreeMap<Integer, String>();
int paramCount = paramAnnotations.length;
for (int paramIndex = 0; paramIndex < paramCount; paramIndex++) {
/*特殊参数忽略*/
if (isSpecialParameter(paramTypes[paramIndex])) {
continue;
}
String name = null;
for (Annotation annotation : paramAnnotations[paramIndex]) {
if (annotation instanceof Param) {
hasParamAnnotation = true;
//如果参数注解了@Param，获取注解的value属性值
name = ((Param) annotation).value();
break;
}
}
if (name == null) {
//默认为true，可以配置
if (config.isUseActualParamName()) {
//反射获取参数的真实名称
name = getActualParamName(method, paramIndex);
}
if (name == null) {
//如果没有办法加载java.lang.reflect.Parameter字节码，name就可能为null，这时用参数的下标作为name
name = String.valueOf(map.size());
}
}
map.put(paramIndex, name); //下标和name做映射
}
names = Collections.unmodifiableSortedMap(map);
}

ParamNameResolver：

private static boolean isSpecialParameter(Class<?> clazz) {
return RowBounds.class.isAssignableFrom(clazz) || ResultHandler.class.isAssignableFrom(clazz);
}

特殊参数就是RowBounds或ResultHandler类型的参数。构建好MapperMethod后，调用其execute方法执行：

public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
switch (command.getType()) {
case INSERT: {
/*将参数转换为sql命令的参数*/
Object param = method.convertArgsToSqlCommandParam(args);
/*插入，返回影响行数的结果*/
result = rowCountResult(sqlSession.insert(command.getName(), param));
break;
}
case UPDATE: {
/*将参数转换为sql命令的参数*/
Object param = method.convertArgsToSqlCommandParam(args);
/*更新，返回影响行数的结果*/
result = rowCountResult(sqlSession.update(command.getName(), param));
break;
}
case DELETE: {
/*将参数转换为sql命令的参数*/
Object param = method.convertArgsToSqlCommandParam(args);
/*删除，返回影响行数的结果*/
result = rowCountResult(sqlSession.delete(command.getName(), param));
break;
}
case SELECT:
//下面几个分支判断的条件，我们在分析构造MapperMethod的过程时看到了这些波尔条件的赋值过程
if (method.returnsVoid() && method.hasResultHandler()) {
/*返回void并且方法包含ResultHandler的查询的执行*/
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {
/*多个返回值的查询的执行*/
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
/*@MapKey注解的Map类型的返回值的查询的执行*/
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {
/*Cursor游标类型的返回值的查询的执行*/
result = executeForCursor(sqlSession, args);
} else {
/*将参数转换为sql命令的参数*/
Object param = method.convertArgsToSqlCommandParam(args);
/*单个返回值的查询的执行*/
result = sqlSession.selectOne(command.getName(), param);
}
break;
case FLUSH:
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + command.getName());
}
//命令执行结果为null，并且方法返回值是基本类型抛出异常
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;
}

下面我们来逐个分析各种返回类型的查询的执行流程：

private void executeWithResultHandler(SqlSession sqlSession, Object[] args) {
MappedStatement ms = sqlSession.getConfiguration().getMappedStatement(command.getName());
//使用ResultHandler作为方法参数，方法需要有@ResultMap或@ResultType注解，或者在mapper配置文件中定义了resultType属性
if (void.class.equals(ms.getResultMaps().get(0).getType())) {
throw new BindingException("method " + command.getName()
+ " needs either a @ResultMap annotation, a @ResultType annotation,"
+ " or a resultType attribute in XML so a ResultHandler can be used as a parameter.");
}
/*将参数转换为sql命令的参数*/
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
//如果方法参数中包含RowBounds类型的参数，提取这个参数，构造MapperMethod时计算了RowBounds类型参数在方法参数列表的下标值
RowBounds rowBounds = method.extractRowBounds(args);
/*提取ResultHandler类型的参数，携带RowBounds查询*/
sqlSession.select(command.getName(), param, rowBounds, method.extractResultHandler(args));
} else {
/*提取ResultHandler类型的参数，不带RowBounds查询*/
sqlSession.select(command.getName(), param, method.extractResultHandler(args));
}
}

MapperMethod：

public Object convertArgsToSqlCommandParam(Object[] args) {
/*获取命名参数*/
return paramNameResolver.getNamedParams(args);
}

ParamNameResolver：

public Object getNamedParams(Object[] args) {
final int paramCount = names.size();
if (args == null || paramCount == 0) {
return null; //解析的参数名称为空，返回null
} else if (!hasParamAnnotation && paramCount == 1) {
//没有注解@Param的参数并且解析的参数名称只有一个，根据下标返回参数
return args[names.firstKey()];
} else {
final Map<String, Object> param = new ParamMap<Object>();
int i = 0;
for (Map.Entry<Integer, String> entry : names.entrySet()) {
//添加参数命名和参数值的对应关系
param.put(entry.getValue(), args[entry.getKey()]);
//通用的参数名称，param1，param2...
final String genericParamName = GENERIC_NAME_PREFIX + String.valueOf(i + 1);
if (!names.containsValue(genericParamName)) {
//添加通用参数名称和参数值的对应关系
param.put(genericParamName, args[entry.getKey()]);
}
i++;
}
return param;
}
}

DefaultSqlSession：

public void select(String statement, Object parameter, ResultHandler handler) {
select(statement, parameter, RowBounds.DEFAULT, handler);
}

没有RowBounds参数的select方法会用默认的RowBounds来调用重载的携带RowBounds参数的select方法。

DefaultSqlSession：

public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
try {
//根据statementId获取MappedStatement
MappedStatement ms = configuration.getMappedStatement(statement);
/*包装集合类型的参数，调用执行器的相关方法查询*/
executor.query(ms, wrapCollection(parameter), rowBounds, handler);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}

DefaultSqlSession：

private Object wrapCollection(final Object object) {
if (object instanceof Collection) {
StrictMap<Object> map = new StrictMap<Object>();
map.put("collection", object);
if (object instanceof List) {
map.put("list", object);
}
return map;
} else if (object != null && object.getClass().isArray()) {
StrictMap<Object> map = new StrictMap<Object>();
map.put("array", object);
return map;
}
return object;
}

对集合类型参数的包装，就是如果参数是集合类型，会根据参数类型的不同为参数添加不同的key。我们在之前的分析看到，这里的executor在默认配置的情况下的类型是CachingExecutor：

public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
/*获取解析过动态标签的sql*/
BoundSql boundSql = ms.getBoundSql(parameterObject);
//创建缓存key
CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
/*调用另一个重载的查询方法进行查询*/
return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}

关于Mybatis缓存的内容我们会用单独的文章进行分析。

MappedStatement：

public BoundSql getBoundSql(Object parameterObject) {
/*获取解析过动态标签的sql*/
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings == null || parameterMappings.isEmpty()) {
boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject);
}
//检查参数映射中是否存在嵌套的resultMap并设置boolean标记
for (ParameterMapping pm : boundSql.getParameterMappings()) {
String rmId = pm.getResultMapId();
if (rmId != null) {
ResultMap rm = configuration.getResultMap(rmId);
if (rm != null) {
hasNestedResultMaps |= rm.hasNestedResultMaps();
}
}
}
return boundSql;
}

在Mybatis标签解析的文章中我们看到，在创建SqlSource时，会根据解析标签时判断的是否是动态标签的结果来创建不同的SqlSource，这里我们以DynamicSqlSource为例进行分析：

public BoundSql getBoundSql(Object parameterObject) {
DynamicContext context = new DynamicContext(configuration, parameterObject);
//这里会根据动态标签的不同，如<if/>、<foreach/>等，解析这些节点拼接到sql中，会涉及到OGNL表达式解析的内容，有兴趣的读者可以自行了解
rootSqlNode.apply(context);
SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
//将#{}替换成?号占位符，并构建每个占位符对应参数属性的映射
SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings());
//将解析内容封装到BoundSql对象中返回
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) {
boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
}
return boundSql;
}

CachingExecutor：

public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
throws SQLException {
Cache cache = ms.getCache();
if (cache != null) {
flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {
ensureNoOutParams(ms, parameterObject, boundSql);
@SuppressWarnings("unchecked")
List<E> list = (List<E>) tcm.getObject(cache, key);
if (list == null) {
/*查询*/
list = delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
tcm.putObject(cache, key, list);
}
return list;
}
}
/*查询*/
return delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}

同样，我们先忽略缓存，继续分析查询的流程：

BaseExecutor：

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());
if (closed) {
throw new ExecutorException("Executor was closed.");
}
if (queryStack == 0 && ms.isFlushCacheRequired()) {
clearLocalCache();
}
List<E> list;
try {
queryStack++;
list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
/*数据库查询*/
list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
queryStack--;
}
if (queryStack == 0) {
for (DeferredLoad deferredLoad : deferredLoads) {
deferredLoad.load();
}
deferredLoads.clear();
if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
clearLocalCache();
}
}
return list;
}

BaseExecutor：

private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List<E> list;
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
/*子类实现具体的查询逻辑*/
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {
localCache.removeObject(key);
}
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
localOutputParameterCache.putObject(key, parameter);
}
return list;
}

SimpleExecutor：

public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
/*创建StatementHandler*/
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
/*准备Statement*/
stmt = prepareStatement(handler, ms.getStatementLog());
/*查询*/
return handler.<E>query(stmt, resultHandler);
} finally {
closeStatement(stmt); //关闭statement
}
}

Configuration：

public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
/*构造RoutingStatementHandler*/
StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
//拦截器执行
statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
return statementHandler;
}

RoutingStatementHandler：

public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
//根据statementType配置选择不同的处理器，在标签解析时我们看到默认为PREPARED
switch (ms.getStatementType()) {
case STATEMENT:
delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
case PREPARED:
delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
case CALLABLE:
delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
default:
throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
}
}

SimpleExecutor：

private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
//获取数据库连接
Connection connection = getConnection(statementLog);
/*准备Statement*/
stmt = handler.prepare(connection, transaction.getTimeout());
/*为Statement设置参数*/
handler.parameterize(stmt);
return stmt;
}

RoutingStatementHandler：

public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
return delegate.prepare(connection, transactionTimeout);
}

BaseStatementHandler：

public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
ErrorContext.instance().sql(boundSql.getSql());
Statement statement = null;
try {
/*实例化Statement*/
statement = instantiateStatement(connection);
/*设置超时时间*/
setStatementTimeout(statement, transactionTimeout);
/*设置FetchSize*/
setFetchSize(statement);
return statement;
} catch (SQLException e) {
closeStatement(statement); //异常关闭Statement
throw e;
} catch (Exception e) {
closeStatement(statement); //异常关闭Statement
throw new ExecutorException("Error preparing statement.  Cause: " + e, e);
}
}

PreparedStatementHandler：

protected Statement instantiateStatement(Connection connection) throws SQLException {
String sql = boundSql.getSql();
if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {
String[] keyColumnNames = mappedStatement.getKeyColumns();
if (keyColumnNames == null) {
return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);
} else {
return connection.prepareStatement(sql, keyColumnNames);
}
} else if (mappedStatement.getResultSetType() != null) {
return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
} else {
return connection.prepareStatement(sql);
}
}

实例化Statement就是根据配置不同调用Connection的不同重载方法来创建PreparedStatement，具体每个重载的方法的作用，请参考Java API。

BaseStatementHandler：

protected void setStatementTimeout(Statement stmt, Integer transactionTimeout) throws SQLException {
Integer queryTimeout = null;
//标签上配置的timeout优先级最高
if (mappedStatement.getTimeout() != null) {
queryTimeout = mappedStatement.getTimeout();
} else if (configuration.getDefaultStatementTimeout() != null) {
//标签没有配置则应用全局配置的timeout
queryTimeout = configuration.getDefaultStatementTimeout();
}
if (queryTimeout != null) {
stmt.setQueryTimeout(queryTimeout);
}
/*应用事务超时时间*/
StatementUtil.applyTransactionTimeout(stmt, queryTimeout, transactionTimeout);
}

StatementUtil：

public static void applyTransactionTimeout(Statement statement, Integer queryTimeout, Integer transactionTimeout) throws SQLException {
if (transactionTimeout == null){
return;
}
Integer timeToLiveOfQuery = null;
//没有配置查询超时时间则应用事务配置的超时时间
if (queryTimeout == null || queryTimeout == 0) {
timeToLiveOfQuery = transactionTimeout;
} else if (transactionTimeout < queryTimeout) {
//如果事务配置的超时时间小于配置的查询超时时间，则应用事务配置的超时时间
timeToLiveOfQuery = transactionTimeout;
}
if (timeToLiveOfQuery != null) {
statement.setQueryTimeout(timeToLiveOfQuery);
}
}

BaseStatementHandler：

protected void setFetchSize(Statement stmt) throws SQLException {
//标签上配置的优先
Integer fetchSize = mappedStatement.getFetchSize();
if (fetchSize != null) {
stmt.setFetchSize(fetchSize);
return;
}
Integer defaultFetchSize = configuration.getDefaultFetchSize();
if (defaultFetchSize != null) {
//标签上没有配置则使用全局配置
stmt.setFetchSize(defaultFetchSize);
}
}

RoutingStatementHandler：

public void parameterize(Statement statement) throws SQLException {
/*为Statement设置参数*/
delegate.parameterize(statement);
}

PreparedStatementHandler：

public void parameterize(Statement statement) throws SQLException {
/*为Statement设置参数*/
parameterHandler.setParameters((PreparedStatement) statement);
}

DefaultParameterHandler：

public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
//遍历参数绑定映射列表
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
//获取参数绑定的属性名称
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);
//根据属性名称从参数对象中反射获取对应的值
value = metaObject.getValue(propertyName);
}
//获取类型处理器
TypeHandler typeHandler = parameterMapping.getTypeHandler();
//获取jdbcType类型
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
/*为PreparedStatement设置值*/
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
} catch (SQLException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
}
}
}
}
}

BaseTypeHandler：

public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
if (parameter == null) {
if (jdbcType == null) {
throw new TypeException("JDBC requires that the JdbcType must be specified for all nullable parameters.");
}
try {
//设置空值
ps.setNull(i, jdbcType.TYPE_CODE);
} catch (SQLException e) {
throw new TypeException("Error setting null for parameter #" + i + " with JdbcType " + jdbcType + " . " +
"Try setting a different JdbcType for this parameter or a different jdbcTypeForNull configuration property. " +
"Cause: " + e, e);
}
} else {
try {
//子类实现具体的非空值设置
setNonNullParameter(ps, i, parameter, jdbcType);
} catch (Exception e) {
throw new TypeException("Error setting non null for parameter #" + i + " with JdbcType " + jdbcType + " . " +
"Try setting a different JdbcType for this parameter or a different configuration property. " +
"Cause: " + e, e);
}
}
}

这里根据构建ParameterMapping时设置的TypeHandler来为PreparedStatement设置对应类型的值。

RoutingStatementHandler：

public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
/*查询*/
return delegate.<E>query(statement, resultHandler);
}

PreparedStatementHandler：

public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
ps.execute(); //执行sql命令
/*处理结果集*/
return resultSetHandler.<E> handleResultSets(ps);
}

查询结果集的处理我们会用单独的文章来分析，下面我们来看其他类型的查询：

private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
List<E> result;
//将参数转换为sql命令的参数，已经分析过
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
//携带RowBounds类型参数的查询
result = sqlSession.<E>selectList(command.getName(), param, rowBounds);
} else {
//不带RowBounds类型参数的查询
result = sqlSession.<E>selectList(command.getName(), param);
}
//如果方法的返回值类型与返回结果的类型不同需要做转换
if (!method.getReturnType().isAssignableFrom(result.getClass())) {
if (method.getReturnType().isArray()) {
/*转换成数组*/
return convertToArray(result);
} else {
/*转换成声明的集合类型*/
return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
}
}
return result;
}

这里的查询过程与我们上文分析的查询过程是一样的，不同的是这里的参数不携带ResultHandler。

MapperMethod：

private <E> Object convertToArray(List<E> list) {
//获取数组组件类型的Class
Class<?> arrayComponentType = method.getReturnType().getComponentType();
//创建与返回结果集同样大小的数组
Object array = Array.newInstance(arrayComponentType, list.size());
if (arrayComponentType.isPrimitive()) {
for (int i = 0; i < list.size(); i++) {
//如果是基本类型需要逐个设置值，因为集合的泛型不允许声明为基本类型
Array.set(array, i, list.get(i));
}
return array;
} else {
//直接将集合转换成数组
return list.toArray((E[])array);
}
}

MapperMethod：

private <E> Object convertToDeclaredCollection(Configuration config, List<E> list) {
/*创建返回集合，objectFactory可以配置，默认为DefaultObjectFactory*/
Object collection = config.getObjectFactory().create(method.getReturnType());
MetaObject metaObject = config.newMetaObject(collection);
//将结果集添加到返回集合中
metaObject.addAll(list);
return collection;
}

DefaultObjectFactory：

public <T> T create(Class<T> type) {
/*创建返回集合/
return create(type, null, null);
}

DefaultObjectFactory：

public <T> T create(Class<T> type, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
/*解析返回集合类型*/
Class<?> classToCreate = resolveInterface(type);
//反射实例化返回集合
return (T) instantiateClass(classToCreate, constructorArgTypes, constructorArgs);
}

DefaultObjectFactory：

protected Class<?> resolveInterface(Class<?> type) {
Class<?> classToCreate;
if (type == List.class || type == Collection.class || type == Iterable.class) {
classToCreate = ArrayList.class;
} else if (type == Map.class) {
classToCreate = HashMap.class;
} else if (type == SortedSet.class) {
classToCreate = TreeSet.class;
} else if (type == Set.class) {
classToCreate = HashSet.class;
} else {
classToCreate = type;
}
return classToCreate;
}

方法的目的就是根据返回集合的类型来确认实例化集合的类型。其他几种查询类型我们简单说明一下，就不一一详细分析了，查询流程都大同小异。executeForMap方法会用DefaultMapResultHandler对返回结果集合进行处理；Cursor游标查询也同样是对返回结果集的特殊处理，感兴趣的同学可以自行查阅资料进行学习；单条结果查询的流程与多值结果的查询流程相同，不同的是会校验返回结果集合的大小不能大于1，然后返回null或者取出集合中的单条记录。到这里，Mybatis查询流程的源码解析就完成了，下篇文章我们来分析Mybatis的写操作。