spring的JdbcTemplate封裝了jdbc的實現，下面通過源代碼看一下其實現
1，一個執行Statement回調的接口
public?interface?StatementCallback?
{
??????Object?doInStatement(Statement?stmt)?throws?SQLException,?DataAccessException;
????}
??public?Object?execute(StatementCallback?action)?throws?DataAccessException?{
??????//獲取線程的同一個連接
??????Connection?con?=?DataSourceUtils.getConnection(getDataSource());
??????Statement?stmt?=?null;
??????try?{
??????????Connection?conToUse?=?con;
??
??????????if?(this.nativeJdbcExtractor?!=?null?&&
??????????????this.nativeJdbcExtractor.
??????????????isNativeConnectionNecessaryForNativeStatements())?{
??????????????//通過特定廠商的特定方法，獲取特定廠商的連接
??????????????conToUse?=?this.nativeJdbcExtractor.getNativeConnection(con);
??????????}
??????????stmt?=?conToUse.createStatement();
??????????//計算并調用stmt.setQueryTimeout(..)
??????????DataSourceUtils.applyTransactionTimeout(stmt,?getDataSource());
??????????Statement?stmtToUse?=?stmt;
??????????if?(this.nativeJdbcExtractor?!=?null)?{
??????????????stmtToUse?=?this.nativeJdbcExtractor.getNativeStatement(stmt);
??????????}
??????????//執行回調
??????????Object?result?=?action.doInStatement(stmtToUse);
??????????SQLWarning?warning?=?stmt.getWarnings();
??????????throwExceptionOnWarningIfNotIgnoringWarnings(warning);
??????????return?result;
??????}?catch?(SQLException?ex)?{
??????????//對異常進行轉譯，所有拋出異常都繼承DataAccessException這個非受控異常
??????????throw?getExceptionTranslator().translate(
??????????????????"executing?StatementCallback",?getSql(action),?ex);
??????}?finally?{
??????????JdbcUtils.closeStatement(stmt);
??????????DataSourceUtils.releaseConnection(con,?getDataSource());
??????}
??}2，一個StatementCallback預定義實現，提供query接口
public?Object?query(final?String?sql,?final?ResultSetExtractor?rse)?throws?DataAccessException?{
???if?(sql?==?null)?{
??????????throw?new?InvalidDataAccessApiUsageException("SQL?must?not?be?null");
??????}
??????if?(JdbcUtils.countParameterPlaceholders(sql,?'?',?"'\"")?>?0)?{
??????????throw?new?InvalidDataAccessApiUsageException(
??????????????????"Cannot?execute?["?+?sql?+
??????????????????"]?as?a?static?query:?it?contains?bind?variables");
??????}
??????if?(logger.isDebugEnabled())?{
??????????logger.debug("Executing?SQL?query?["?+?sql?+?"]");
??????}
??????//執行回調的內部類
??????class?QueryStatementCallback?implements?StatementCallback,?SqlProvider?{
??????????public?Object?doInStatement(Statement?stmt)?throws?SQLException?{
??????????????ResultSet?rs?=?null;
??????????????try?{
??????????????????if?(getFetchSize()?>?0)?{
??????????????????????stmt.setFetchSize(getFetchSize());
??????????????????}
??????????????????if?(getMaxRows()?>?0)?{
??????????????????????stmt.setMaxRows(getMaxRows());
??????????????????}
??????????????????rs?=?stmt.executeQuery(sql);
??????????????????ResultSet?rsToUse?=?rs;
??????????????????if?(nativeJdbcExtractor?!=?null)?{
??????????????????????rsToUse?=?nativeJdbcExtractor.getNativeResultSet(rs);
??????????????????}
??????????????????//又一個回調
??????????????????return?rse.extractData(rsToUse);
??????????????}?finally?{
??????????????????JdbcUtils.closeResultSet(rs);
??????????????}
??????????}
??????????public?String?getSql()?{
??????????????return?sql;
??????????}
??????}
??????return?execute(new?QueryStatementCallback());
??} 3，看一下一個預定義的ResultSetExtractor實現
??private?static?class?RowCallbackHandlerResultSetExtractor?implements?ResultSetExtractor?{
????????private?final?RowCallbackHandler?rch;
????????public?RowCallbackHandlerResultSetExtractor(RowCallbackHandler?rch)?{
????????????this.rch?=?rch;
????????}
????????public?Object?extractData(ResultSet?rs)?throws?SQLException?{
????????????//利用RowCallbackHandler處理resultset，返回處理結果List
????????????while?(rs.next())?{
????????????????this.rch.processRow(rs);
????????????}
????????????if?(this.rch?instanceof?ResultReader)?{
????????????????return?((ResultReader)?this.rch).getResults();
????????????}
????????????else?{
????????????????return?null;
????????????}
????????}
????}
????
????public?interface?ResultReader?extends?RowCallbackHandler?{
?????
????????/**?*//**
?????????*?Return?all?results,?disconnected?from?the?JDBC?ResultSet.
?????????*?Never?returns?null;?returns?the?empty?collection?if?there
?????????*?were?no?results.
?????????*/
????????List?getResults();
????}
????
????
????public?class?RowMapperResultReader?implements?ResultReader?{
????????/**?*//**?List?to?save?results?in?*/
????????private?final?List?results;
????
????????/**?*//**?The?RowMapper?implementation?that?will?be?used?to?map?rows?*/
????????private?final?RowMapper?rowMapper;
????
????????/**?*//**?The?counter?used?to?count?rows?*/
????????private?int?rowNum?=?0;
????
????????/**?*//**
?????????*?Create?a?new?RowMapperResultReader.
?????????*?@param?rowMapper?the?RowMapper?which?creates?an?object?for?each?row
?????????*/
????????public?RowMapperResultReader(RowMapper?rowMapper)?{
????????????this(rowMapper,?0);
????????}
????
????????/**?*//**
?????????*?Create?a?new?RowMapperResultReader.
?????????*?@param?rowMapper?the?RowMapper?which?creates?an?object?for?each?row
?????????*?@param?rowsExpected?the?number?of?expected?rows
?????????*?(just?used?for?optimized?collection?handling)
?????????*/
????????public?RowMapperResultReader(RowMapper?rowMapper,?int?rowsExpected)?{
????????????//?Use?the?more?efficient?collection?if?we?know?how?many?rows?to?expect:
????????????//?ArrayList?in?case?of?a?known?row?count,?LinkedList?if?unknown
????????????this.results?=?(rowsExpected?>?0)???(List)?new?ArrayList(rowsExpected)?:?(List)?new?LinkedList();
????????????this.rowMapper?=?rowMapper;
????????}
????
????????public?void?processRow(ResultSet?rs)?throws?SQLException?{
????????????this.results.add(this.rowMapper.mapRow(rs,?this.rowNum++));
????????}
????
????????public?List?getResults()?{
????????????return?this.results;
????????}
????} ?4，連接是如何獲取的
????public?abstract?class?DataSourceUtils?{
????????
????????//..
????????
????????public?static?Connection?doGetConnection(DataSource?dataSource)?throws?SQLException?{
????????????Assert.notNull(dataSource,?"No?DataSource?specified");
????????????//利用ThreadLocal，獲取當前線程對應dataSource的connection封裝---ConnectionHolder
????????????ConnectionHolder?conHolder?=?(ConnectionHolder)?TransactionSynchronizationManager.getResource(dataSource);
????????????if?(conHolder?!=?null)?{
????????????????conHolder.requested();
????????????????return?conHolder.getConnection();
????????????}
????????????//如果conHolder為空,為當前線程獲取一個新連接，并設置ThreadLocal
????????????logger.debug("Opening?JDBC?Connection");
????????????Connection?con?=?dataSource.getConnection();
????????????
????????????if?(TransactionSynchronizationManager.isSynchronizationActive())?{
????????????????logger.debug("Registering?transaction?synchronization?for?JDBC?Connection");
????????????????//?Use?same?Connection?for?further?JDBC?actions?within?the?transaction.
????????????????//?Thread-bound?object?will?get?removed?by?synchronization?at?transaction?completion.
????????????????conHolder?=?new?ConnectionHolder(con);
????????????????conHolder.setSynchronizedWithTransaction(true);
????????????????conHolder.requested();
????????????????TransactionSynchronizationManager.registerSynchronization(
????????????????????????new?ConnectionSynchronization(conHolder,?dataSource));
????????????????TransactionSynchronizationManager.bindResource(dataSource,?conHolder);
????????????}
????
????????????return?con;
????????}
????????//注意異常的改變
????????public?static?Connection?getConnection(DataSource?dataSource)?throws?CannotGetJdbcConnectionException?{
????????????try?{
????????????????return?doGetConnection(dataSource);
????????????}
????????????catch?(SQLException?ex)?{
????????????????throw?new?CannotGetJdbcConnectionException("Could?not?get?JDBC?Connection",?ex);
????????????}
????????}
????} 5，getResource和bindResource實現
????public?abstract?class?TransactionSynchronizationManager?{
????????
????????//..
????????
????????private?static?final?ThreadLocal?resources?=?new?ThreadLocal();
????????private?static?final?ThreadLocal?synchronizations?=?new?ThreadLocal();
????????
????????public?static?Object?getResource(Object?key)?{
????????????Map?map?=?(Map)?resources.get();
????????????if?(map?==?null)?{
????????????????return?null;
????????????}
????????????Object?value?=?map.get(key);
????????????if?(value?!=?null?&&?logger.isDebugEnabled())?{
????????????????logger.debug("Retrieved?value?["?+?value?+?"]?for?key?["?+?key?+?"]?bound?to?thread?["?+
????????????????????????Thread.currentThread().getName()?+?"]");
????????????}
????????????return?value;
????????}
????????public?static?void?bindResource(Object?key,?Object?value)?throws?IllegalStateException?{
????????????Map?map?=?(Map)?resources.get();
????????????//?set?ThreadLocal?Map?if?none?found
????????????if?(map?==?null)?{
????????????????map?=?new?HashMap();
????????????????resources.set(map);
????????????}
????????????if?(map.containsKey(key))?{
????????????????throw?new?IllegalStateException("Already?value?["?+?map.get(key)?+?"]?for?key?["?+?key?+
????????????????????????"]?bound?to?thread?["?+?Thread.currentThread().getName()?+?"]");
????????????}
????????????map.put(key,?value);
????????????if?(logger.isDebugEnabled())?{
????????????????logger.debug("Bound?value?["?+?value?+?"]?for?key?["?+?key?+?"]?to?thread?["?+
????????????????????????Thread.currentThread().getName()?+?"]");
????????????}
????????}
????} 6，ConnectionHolder?類
public?class?ConnectionHolder?extends?ResourceHolderSupport?{
????private?final?ConnectionHandle?connectionHandle;
????private?Connection?currentConnection;
????/**?*//**
?????*?Create?a?new?ConnectionHolder?for?the?given?ConnectionHandle.
?????*?@param?connectionHandle?the?ConnectionHandle?to?hold
?????*/
????public?ConnectionHolder(ConnectionHandle?connectionHandle)?{
????????this.connectionHandle?=?connectionHandle;
????}
????/**?*//**
?????*?Create?a?new?ConnectionHolder?for?the?given?JDBC?Connection,
?????*?wrapping?it?with?a?SimpleConnectionHandle.
?????*?@param?connection?the?JDBC?Connection?to?hold
?????*?@see?SimpleConnectionHandle
?????*/
????public?ConnectionHolder(Connection?connection)?{
????????this.connectionHandle?=?new?SimpleConnectionHandle(connection);
????}
????/**?*//**
?????*?Return?the?ConnectionHandle?held?by?this?ConnectionHolder.
?????*/
????public?ConnectionHandle?getConnectionHandle()?{
????????return?connectionHandle;
????}
????/**?*//**
?????*?Return?the?current?Connection?held?by?this?ConnectionHolder.
?????*?<p>This?will?be?the?same?Connection?until?<code>released</code>
?????*?gets?called?on?the?ConnectionHolder,?which?will?reset?the
?????*?held?Connection,?fetching?a?new?Connection?on?demand.
?????*?@see?ConnectionHandle#getConnection()
?????*?@see?#released()
?????*/
????public?Connection?getConnection()?{
????????if?(this.currentConnection?==?null)?{
????????????this.currentConnection?=?this.connectionHandle.getConnection();
????????}
????????return?this.currentConnection;
????}
????/**?*//**
?????*?Releases?the?current?Connection?held?by?this?ConnectionHolder.
?????*?<p>This?is?necessary?for?ConnectionHandles?that?expect?"Connection?borrowing",
?????*?where?each?returned?Connection?is?only?temporarily?leased?and?needs?to?be
?????*?returned?once?the?data?operation?is?done,?to?make?the?Connection?available
?????*?for?other?operations?within?the?same?transaction.?This?is?the?case?with
?????*?JDO?2.0?DataStoreConnections,?for?example.
?????*?@see?org.springframework.orm.jdo.DefaultJdoDialect#getJdbcConnection
?????*/
????public?void?released()?{
????????super.released();
????????if?(this.currentConnection?!=?null)?{
????????????this.connectionHandle.releaseConnection(this.currentConnection);
????????????this.currentConnection?=?null;
????????}
????}
} public?class?SimpleConnectionHandle?implements?ConnectionHandle?{
????private?final?Connection?connection;
????/**?*//**
?????*?Create?a?new?SimpleConnectionHandle?for?the?given?Connection.
?????*?@param?connection?the?JDBC?Connection
?????*/
????public?SimpleConnectionHandle(Connection?connection)?{
????????this.connection?=?connection;
????}
????public?Connection?getConnection()?{
????????return?connection;
????}
????public?void?releaseConnection(Connection?con)?{
????}
????public?String?toString()?{
????????return?"SimpleConnectionHandle:?"?+?this.connection;
????}
}