MyBatis核心源碼深度剖析SQL語句執行過程
1 SQL語句的執行過程介紹
MyBatis核心執行組件：
2 SQL執行的入口分析
2.1 為Mapper接口創建代理對象
// 方式1：
User user = session.selectOne("com.oldlu.dao.UserMapper.findUserById", 101);
// 方式2：
UserMapper mapper = session.getMapper(UserMapper.class);
List<User> userList = mapper.findAll();
2.2 執行代理邏輯
方式1入口分析：
session是DefaultSqlSession類型的，因為sqlSessionFactory默認生成的SqlSession是
DefaultSqlSession類型。
selectOne()會調用selectList()。
// DefaultSqlSession類
public <E> List<E> selectList(String statement, Object parameter, RowBounds
rowBounds) {
try {
MappedStatement ms = configuration.getMappedStatement(statement);
// CURD操作是交給Excetor去處理的
return executor.query(ms, wrapCollection(parameter), rowBounds,
Executor.NO_RESULT_HANDLER);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: "
+ e, e);
} finally {
ErrorContext.instance().reset();
}
}
方式2入口分析：
獲取代理對象：
//DefaultSqlSession類 ====================>
@Override
public <T> T getMapper(Class<T> type) {
return configuration.getMapper(type, this);
}
// Configuration類 ====================>
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
//MapperRegistry ----> apperProxyFactory.newInstance ====================>
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
//從緩存中獲取該Mapper接口的代理工廠對象
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>)
knownMappers.get(type);
//如果該Mapper接口沒有註冊過，則拋異常
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the
MapperRegistry.");
}
try {
//【使用代理工廠創建Mapper接口的代理對象】
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e,
e);
}
}
//MapperProxyFactory --->此時生成代理對象 ====================>
protected T newInstance(MapperProxy<T> mapperProxy) {
//Mybatis底層是調用JDK的Proxy類來創建代理實例
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new
Class[] { mapperInterface }, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession,
mapperInterface, methodCache);
return newInstance(mapperProxy);
}
代理對象執行邏輯：
//MapperProxy ====================>
/**代理對象執行的方法，代理以後，所有Mapper的方法調用時，都會調用這個invoke方法*/
public Object invoke(Object proxy, Method method, Object[] args) throws
Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
//如果是Object方法，則調用方法本身
return method.invoke(this, args);
} else {
//調用接口方法：根據被調用接口的Method對象，從緩存中獲取MapperMethodInvoker對象
//apper接口中的每一個方法都對應一個MapperMethodInvoker對象，而MapperMethodInvoker
對象裡面的MapperMethod保存著對應的SQL信息和返回類型以完成SQL調用 ...
return cachedInvoker(method).invoke(proxy, method, args, sqlSession);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}
/**
獲取緩存中MapperMethodInvoker，如果沒有則創建一個，而MapperMethodInvoker內部封裝這一
個MethodHandler
*/
private MapperMethodInvoker cachedInvoker(Method method) throws Throwable {
try {
return methodCache.computeIfAbsent(method, m -> {
if (m.isDefault()) {
//如果調用接口的是默認方法（default方法）
try {
if (privateLookupInMethod == null) {
return new
DefaultMethodInvoker(getMethodHandleJava8(method));
} else {
return new
DefaultMethodInvoker(getMethodHandleJava9(method));
}
} catch (IllegalAccessException | InstantiationException |
InvocationTargetException
| NoSuchMethodException e) {
throw new RuntimeException(e);
}
} else {
//如果調用的普通方法（非default方法），則創建一個PlainMethodInvoker並放
入緩存，其中MapperMethod保存對應接口方法的SQL以及入參和出參的數據類型等信息
return new PlainMethodInvoker(new MapperMethod(mapperInterface,
method, sqlSession.getConfiguration()));
}
});
} catch (RuntimeException re) {
Throwable cause = re.getCause();
throw cause == null ? re : cause;
}
}
// MapperProxy內部類： PainMethodInvoker ====================>
// 當cacheInvoker返回瞭PalinMethodInvoker實例之後，緊接著調用瞭這個實例的
PlainMethodInvoker:invoke方法
@Override
public Object invoke(Object proxy, Method method, Object[] args, SqlSession
sqlSession) throws Throwable {
//Mybatis實現接口方法的核心: MapperMethod::execute方法：
return mapperMethod.execute(sqlSession, args);
}
// MapperMethod ====================>
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
switch (command.getType()) {
case INSERT: {
// 將args進行解析，如果是多個參數則，則根據@Param註解指定名稱將參數轉換為Map，
如果是封裝實體則不轉換
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:
//查詢操作
if (method.returnsVoid() && method.hasResultHandler()) {
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {
result = executeForCursor(sqlSession, args);
} else {
//解析參數，因為SqlSession::selectOne方法參數隻能傳入一個，但是我們
Mapper中可能傳入多個參數，
//有可能是通過@Param註解指定參數名，所以這裡需要將Mapper接口方法中的多個參
數轉化為一個ParamMap,
//也就是說如果是傳入的單個封裝實體，那麼直接返回出來；如果傳入的是多個參數，
實際上都轉換成瞭Map
Object param = method.convertArgsToSqlCommandParam(args);
//可以看到動態代理最後還是使用SqlSession操作數據庫的
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;
}
// 此時我們發現： 回到瞭sqlsession中
private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
List<E> result;
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
result = sqlSession.selectList(command.getName(), param, rowBounds);
} else {
result = sqlSession.selectList(command.getName(), param);
}
// ...
return result;
}
3 查詢語句的執行過程分析
3.1 selectOne方法分析
// DefaultSqlSession類 ===============>
// selectOne
@Override
public <T> T selectOne(String statement, Object parameter) {
// //selectOne()會調用selectList()。
List<T> list = this.selectList(statement, parameter);
if (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 {
return null;
}
}
// selectList
public <E> List<E> selectList(String statement, Object parameter, RowBounds
rowBounds) {
try {
MappedStatement ms = configuration.getMappedStatement(statement);
// CURD操作是交給Excetor去處理的
return executor.query(ms, wrapCollection(parameter), rowBounds,
Executor.NO_RESULT_HANDLER);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: "
+ e, e);
} finally {
ErrorContext.instance().reset();
}
}
3.2 sql獲取
// CachingExecutor ===============>
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds
rowBounds, ResultHandler resultHandler) throws SQLException {
// 獲取綁定的sql命令，比如"SELECT * FROM xxx"
BoundSql boundSql = ms.getBoundSql(parameterObject);
CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
@Override
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, boundSql);
@SuppressWarnings("unchecked")
List<E> list = (List<E>) tcm.getObject(cache, key);
if (list == null) {
list = delegate.query(ms, parameterObject, rowBounds,
resultHandler, key, boundSql);
tcm.putObject(cache, key, list); // issue #578 and #116
}
return list;
}
}
return delegate.query(ms, parameterObject, rowBounds, resultHandler, key,
boundSql);
}
//真正執行query操作的是SimplyExecutor代理來完成的，SimplyExecutor的父類BaseExecutor的
query方法中:
// BaseExecutor類:SimplyExecutor的父類 =================>
@Override
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++;
//localCache是一級緩存，如果找不到就調用queryFromDatabase從數據庫中查找
list = resultHandler == null ? (List<E>) localCache.getObject(key) :
null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
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;
}
//第一次，沒有緩存，所以會調用queryFromDatabase方法來執行查詢。
private <E> List<E> queryFromDatabase(...) throws SQLException {
List<E> list;
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
// 查詢
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類 ============================>
public <E> List<E> doQuery(...) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
StatementHandler handler = configuration.newStatementHandler(....);
// 1：SQL查詢參數的設置
stmt = prepareStatement(handler, ms.getStatementLog());
// StatementHandler封裝瞭Statement
// 2：SQL查詢操作和結果集的封裝
return handler.<E>query(stmt);
} finally {
closeStatement(stmt);
}
}
3.3 參數設置
// SimplyExecutor類 ============================>
// 【1】 參數設置： prepareStatement
private Statement prepareStatement(StatementHandler handler, Log statementLog)
throws SQLException {
Statement stmt;
// 通過getConnection方法來獲取一個Connection，
Connection connection = getConnection(statementLog);
// 調用prepare方法來獲取一個Statement
stmt = handler.prepare(connection, transaction.getTimeout());
// 設置SQL查詢中的參數值 ***
handler.parameterize(stmt);
return stmt;
}
// RoutingStatementHandler ============================>
// PreparedStatementHandler ============================>
@Override
public void parameterize(Statement statement) throws SQLException {
parameterHandler.setParameters((PreparedStatement) statement);
}
// DefaultParameterHandler ============================> 此時參數設置成功
@Override
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting
parameters").object(mappedStatement.getParameterMap().getId());
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
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);
}
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException | SQLException e) {
throw new TypeException("Could not set parameters for
mapping.....");
}
}
}
}
}
3.4 SQL執行和結果集的封裝
// RoutingStatementHandler ============================>
@Override
public <E> List<E> query(Statement statement) throws SQLException {
return delegate.<E>query(statement);
}
// PreparedStatementHandler ============================>
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler)
throws SQLException {
// 這裡就到瞭熟悉的PreparedStatement瞭
PreparedStatement ps = (PreparedStatement) statement;
// 執行SQL查詢操作
ps.execute();
// 結果交給ResultHandler來處理
return resultSetHandler.<E> handleResultSets(ps);
}
// DefaultResultSetHandler類（封裝返回值，將查詢結果封裝成Object對象）
@Override
public List<Object> handleResultSets(Statement stmt) throws SQLException {
ErrorContext.instance().activity("handling
results").object(mappedStatement.getId());
final List<Object> multipleResults = new ArrayList<Object>();
int resultSetCount = 0;
ResultSetWrapper rsw = getFirstResultSet(stmt);
List<ResultMap> resultMaps = mappedStatement.getResultMaps();
int resultMapCount = resultMaps.size();
validateResultMapsCount(rsw, resultMapCount);
while (rsw != null && resultMapCount > resultSetCount) {
ResultMap resultMap = resultMaps.get(resultSetCount);
handleResultSet(rsw, resultMap, multipleResults, null);
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
String[] resultSets = mappedStatement.getResultSets();
if (resultSets != null) {
while (rsw != null && resultSetCount < resultSets.length) {
ResultMapping parentMapping =
nextResultMaps.get(resultSets[resultSetCount]);
if (parentMapping != null) {
String nestedResultMapId = parentMapping.getNestedResultMapId();
ResultMap resultMap =
configuration.getResultMap(nestedResultMapId);
handleResultSet(rsw, resultMap, null, parentMapping);
}
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
}
return collapseSingleResultList(multipleResults);
}
4 更新語句的執行過程分析
- xecutor 的 update 方法分析
- insert、update 和 delete 操作都會清空一二級緩存
- doUpdate 方法
- PreparedStatementHandler 的 update 方法
- 默認是創建PreparedStatementHandler，然後執行prepareStatement方法。
- 執行結果為受影響行數
- 執行更新語句的SQL
4.1 sqlsession增刪改方法分析
// DefaultSqlSession ===============>
@Override
public int insert(...) {
return update(statement, parameter);
}
@Override
public int update(String statement) {
return update(statement, null);
}
@Override
public int delete(...) {
return update(....);
}
// insert 、delete操作是通過調用update語句進行的相關邏輯
@Override
public int update(String statement, Object parameter) {
try {
dirty = true;
MappedStatement ms = configuration.getMappedStatement(statement);
// 增刪改 最終底層都是 update
return executor.update(ms, wrapCollection(parameter));
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error updating database. Cause: " +
e, e);
} finally {
ErrorContext.instance().reset();
}
}
4.2 sql獲取
// CachingExecutor ===============>
@Override
public int update(MappedStatement ms, Object parameterObject) throws
SQLException {
// 執行增刪改，清除緩存
flushCacheIfRequired(ms);
// 跳轉BaseExecutor
return delegate.update(ms, parameterObject);
}
// BaseExecutor ===============>
@Override
public int update(MappedStatement ms, Object parameter) throws SQLException {
ErrorContext.instance().resource(ms.getResource()).activity("executing an
update").object(ms.getId());
if (closed) {
throw new ExecutorException("Executor was closed.");
}
// 清除 LocalCache 一級緩存
clearLocalCache();
//執行 doUpdate
return doUpdate(ms, parameter);
}
// SimpleExecutor ===============>
// doUpdate
@Override
public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
StatementHandler handler = configuration.newStatementHandler(...);
// 【1】.獲取statement,並進行參數映射
stmt = prepareStatement(handler, ms.getStatementLog());
// 【2】.handler.update()方法執行具體sql指令
return handler.update(stmt);
} finally {
closeStatement(stmt);
}
}
4.3 參數設置
// SimplyExecutor類 ============================>
//【1】 prepareStatement
private Statement prepareStatement(StatementHandler handler, Log statementLog)
throws SQLException {
Statement stmt;
Connection connection = getConnection(statementLog);
// 使用connection對象信息創建statement，並將超時時間綁定
stmt = handler.prepare(connection, transaction.getTimeout());
// parameterize方法設置sql執行時候需要的參數
handler.parameterize(stmt);
return stmt;
}
// RoutingStatementHandler ============================>
// PreparedStatementHandler ============================>
@Override
public void parameterize(Statement statement) throws SQLException {
parameterHandler.setParameters((PreparedStatement) statement);
}
// DefaultParameterHandler ============================> 此時參數設置成功
@Override
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting
parameters").object(mappedStatement.getParameterMap().getId());
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
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);
}
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException | SQLException e) {
throw new TypeException("Could not set parameters for
mapping.....");
}
}
}
}
}
4.4 SQL執行
// RoutingStatementHandler ============================>
@Override
public int update(Statement statement) throws SQLException {
return delegate.update(statement);
}
// PreparedStatementHandler ============================>
@Override
public int update(Statement statement) throws SQLException {
// 這裡就是底層JDBC的PreparedStatement 操作瞭
PreparedStatement ps = (PreparedStatement) statement;
// 執行SQL增刪改操作
ps.execute();
// 獲取影響的行數
int rows = ps.getUpdateCount();
Object parameterObject = boundSql.getParameterObject();
KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);
// 返回影響的行數
return rows;
}
5 小結
mybatis執行SQL的流程都是：
1.根據statement字符串從configuration中獲取對應的mappedStatement；
2.根據獲取的mappedStatement創建相應的Statement實例；
3.根據傳入的參數對statement實例進行參數設置；
4.執行statement並執行後置操作；
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