@Override
public List selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
// 根据传入的statementId,获取MappedStatement对象
MappedStatement ms = configuration.getMappedStatement(statement);
// 调用执行器的查询方法
// RowBounds是用来逻辑分页(按照条件将数据从数据库查询到内存中,在内存中进行分页)
// wrapCollection(parameter)是用来装饰集合或者数组参数
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();
}
}
//第一步
@Override
public List query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
// 获取绑定的SQL语句,比如“SELECT * FROM user WHERE id = ? ”
BoundSql boundSql = ms.getBoundSql(parameterObject);
// 生成缓存Key
CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
//第二步
@Override
public List query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
throws SQLException {
// 获取二级缓存
Cache cache = ms.getCache();
if (cache != null) {
// 当为select语句时,flushCache默认为false,表示任何时候语句被调用,都不会去清空本地缓存和二级缓存
// 当为insert、update、delete语句时,useCache默认为true,表示会将本条语句的结果进行二级缓存
// 刷新二级缓存 (存在缓存且flushCache为true时)
flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {
ensureNoOutParams(ms, boundSql);
// 从二级缓存中查询数据
@SuppressWarnings("unchecked")
List list = (List) tcm.getObject(cache, key);
// 如果二级缓存中没有查询到数据,则查询数据库
if (list == null) {
// 委托给BaseExecutor执行
list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
tcm.putObject(cache, key, list); // issue #578 and #116
}
return list;
}
}
// 委托给BaseExecutor执行
return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
@Override
public List 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 list;
try {
queryStack++;
// 从一级缓存中获取数据
list = resultHandler == null ? (List) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
// 如果一级缓存没有数据,则从数据库查询数据
list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
queryStack--;
}
if (queryStack == 0) {
for (DeferredLoad deferredLoad : deferredLoads) {
deferredLoad.load();
}
// issue #601
deferredLoads.clear();
if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
// issue #482
clearLocalCache();
}
}
return list;
}
private List queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List list;
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
// 执行查询
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {
//移除一级缓存中原有值
localCache.removeObject(key);
}
//往一级缓存中存值
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
localOutputParameterCache.putObject(key, parameter);
}
return list;
}
@Override
public List doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler,
BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
// 获取Configuration对象
Configuration configuration = ms.getConfiguration();
// 创建RoutingStatementHandler,用来处理Statement
// RoutingStatementHandler类中初始化delegate类(SimpleStatementHandler、PreparedStatementHandler)
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds,
resultHandler, boundSql);
// 子流程1:设置参数
stmt = prepareStatement(handler, ms.getStatementLog());
// 子流程2:执行SQL语句(已经设置过参数),并且映射结果集
return handler.query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}
public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement,
Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
// 创建路由功能的StatementHandler,根据MappedStatement中的StatementType
StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject,
rowBounds, resultHandler, boundSql);
statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
return statementHandler;
}
public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
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());
}
}
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
// 获取连接
Connection connection = getConnection(statementLog);
// 创建Statement(PreparedStatement、Statement、CallableStatement)
stmt = handler.prepare(connection, transaction.getTimeout());
// SQL参数设置
handler.parameterize(stmt);
return stmt;
}
protected Connection getConnection(Log statementLog) throws SQLException {
Connection connection = transaction.getConnection();
if (statementLog.isDebugEnabled()) {
return ConnectionLogger.newInstance(connection, statementLog, queryStack);
} else {
return connection;
}
}
@Override
public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
ErrorContext.instance().sql(boundSql.getSql());
Statement statement = null;
try {
// 实例化Statement,比如PreparedStatement
statement = instantiateStatement(connection);
// 设置查询超时时间
setStatementTimeout(statement, transactionTimeout);
setFetchSize(statement);
return statement;
} catch (SQLException e) {
closeStatement(statement);
throw e;
} catch (Exception e) {
closeStatement(statement);
throw new ExecutorException("Error preparing statement. Cause: " + e, e);
}
}
@Override
protected Statement instantiateStatement(Connection connection) throws SQLException {
// 获取带有占位符的SQL语句
String sql = boundSql.getSql();
// 处理带有主键返回的SQL
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() == ResultSetType.DEFAULT) {
return connection.prepareStatement(sql);
} else {
return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
}
}
@Override
public void parameterize(Statement statement) throws SQLException {
// 通过ParameterHandler处理参数
parameterHandler.setParameters((PreparedStatement) statement);
}
@Override
public List query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
// 执行PreparedStatement,也就是执行SQL语句
ps.execute();
// 处理结果集
return resultSetHandler.handleResultSets(ps);
}
@Override
public List
页面更新:2024-05-12
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