在spring里面我們一般是這樣來使用模板模式的：
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
jdbcTemplate.update("UPDATE user SET age = 10 WHERE id = 'erica'");
或者：
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
jdbcTemplate
.update(
"UPDATE user SET age = ? WHERE id = ?",
new PreparedStatementSetter() {
public void setValues(PreparedStatementSetter ps)
throws SQLException {
ps.setInt(1, 18);
ps.setString(2, "erica");
}
}
);
那么具體在spring里面他是怎么運作的呢？
下面以query查詢?yōu)槔?/font>
public class JdbcTemplate extends JdbcAccessor implements JdbcOperations, InitializingBean {
。。。。。。。。。。。。。。。。。。。。。。。。。
protected Object query(
PreparedStatementCreator psc, final PreparedStatementSetter pss, final ResultSetExtractor rse)
throws DataAccessException {
if (logger.isDebugEnabled()) {
String sql = getSql(psc);
logger.debug("Executing SQL query" + (sql != null ? " [" + sql + "]" : ""));
}
return execute(psc, new PreparedStatementCallback() {
//此處以 PreparedStatementCallback 為參數(shù)調用 execute（）方法，在execute（）方法里面回調傳入的方法。在回調方法里面即根據(jù)傳入的 PreparedStatement 執(zhí)行 查詢操作，返回結果。而 PreparedStatement 的獲取是在調用回調方法的客戶端實現(xiàn)即在execute（）方法里面獲取，并作為參數(shù)傳給回調方法。
public Object doInPreparedStatement(PreparedStatement ps) throws SQLException {
ResultSet rs = null;
try {
if (pss != null) {
pss.setValues(ps);
}
if (getFetchSize() > 0) {
ps.setFetchSize(getFetchSize());
}
rs = ps.executeQuery();
ResultSet rsToUse = rs;
if (nativeJdbcExtractor != null) {
rsToUse = nativeJdbcExtractor.getNativeResultSet(rs);
}
return rse.extractData(rsToUse);
}
finally {
JdbcUtils.closeResultSet(rs);
if (pss instanceof ParameterDisposer) {
((ParameterDisposer) pss).cleanupParameters();
}
}
}
});
}
那么在execue（）方法里面是怎樣回調的呢？下面看看execue（）方法：
public Object execute(PreparedStatementCreator psc, PreparedStatementCallback action) {
Connection con = DataSourceUtils.getConnection(getDataSource());
PreparedStatement ps = null;
try {
Connection conToUse = con;
if (this.nativeJdbcExtractor != null &&
this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativePreparedStatements()) {
conToUse = this.nativeJdbcExtractor.getNativeConnection(con);
}
ps = psc.createPreparedStatement(conToUse);
DataSourceUtils.applyTransactionTimeout(ps, getDataSource());
PreparedStatement psToUse = ps;
if (this.nativeJdbcExtractor != null) {
psToUse = this.nativeJdbcExtractor.getNativePreparedStatement(ps);
}
Object result = action.doInPreparedStatement(psToUse);
SQLWarning warning = ps.getWarnings();
throwExceptionOnWarningIfNotIgnoringWarnings(warning);
return result;
}
catch (SQLException ex) {
throw getExceptionTranslator().translate(
"executing PreparedStatementCallback [" + psc + "]", getSql(psc), ex);
}
finally {
if (psc instanceof ParameterDisposer) {
((ParameterDisposer) psc).cleanupParameters();
}
JdbcUtils.closeStatement(ps);
DataSourceUtils.closeConnectionIfNecessary(con, getDataSource());
}
}
添加刪除的操作類似，只是他們的實現(xiàn)都在以execute命名的方法里面。
public void execute(final String sql) throws DataAccessException {
if (logger.isDebugEnabled()) {
logger.debug("Executing SQL statement [" + sql + "]");
}
class ExecuteStatementCallback implements StatementCallback, SqlProvider {
public Object doInStatement(Statement stmt) throws SQLException {
stmt.execute(sql);
return null;
}
public String getSql() {
return sql;
}
}
execute(new ExecuteStatementCallback());
}
public Object execute(final StatementCallback action) {
Connection con = DataSourceUtils.getConnection(getDataSource());
Statement stmt = null;
try {
Connection conToUse = con;
if (this.nativeJdbcExtractor != null &&
this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativeStatements()) {
conToUse = this.nativeJdbcExtractor.getNativeConnection(con);
}
stmt = conToUse.createStatement();
DataSourceUtils.applyTransactionTimeout(stmt, getDataSource());
Statement stmtToUse = stmt;
if (this.nativeJdbcExtractor != null) {
stmtToUse = this.nativeJdbcExtractor.getNativeStatement(stmt);
}
Object result = action.doInStatement(stmtToUse);
SQLWarning warning = stmt.getWarnings();
throwExceptionOnWarningIfNotIgnoringWarnings(warning);
return result;
}
catch (SQLException ex) {
throw getExceptionTranslator().translate("executing StatementCallback", getSql(action), ex);
}
finally {
//這里就是我們自己寫程序的時候需要寫的關于數(shù)據(jù)庫鏈接的關閉操作
JdbcUtils.closeStatement(stmt);
DataSourceUtils.closeConnectionIfNecessary(con, getDataSource());
}
}