【发布时间】：2017-03-28 13:30:33
【问题描述】：
最近，我不得不测量我们软件的一些 SQL 请求所花费的时间。为此，我决定采用天真的方法，并通过调用 System.nanoTime() 来围绕查询。 在这样做的同时，我发现一个类（SqlSuggest）在 4 个非常相似的方法中包含 4 个非常相似的查询。我认为重构和重新组合公共部分是个好主意。
这造成了连接泄漏，连接不再关闭。我回滚了重构，但我仍然想了解我做错了什么。
SqlSuggest 类的第一个版本有 4 个方法 getSuggestListByItems、getDisplayValueByItems、getSuggestListByListID 和 getDisplayValueByListeID。这些方法中的每一个都通过另一个类打开和关闭连接、语句和结果集（在 finally 块中）：DBAccess。
该类的第二个版本具有相同的 4 个方法，除了打开和关闭 Connection 之外，它们调用 2 个方法中的 1 个，具体取决于它们需要一个结果还是一个列表。
这 2 个方法（executeQueryGetString 和 executeQueryGetListOfStringArray）分别声明了 Connection、Statement 和 ResultSet，然后调用一个方法：executeQuery，其中 Connection 打开，创建 Statement 并返回 ResultSet。
然后第二层方法从 ResultSet 中提取数据并关闭所有内容。
我猜我错误地认为在一个方法中声明 Connection、Statement 和 ResultSet 可以让我从同一个方法中关闭它们。
这是旧的类（简化）：
public class SqlSuggest {
private final static Logger LOGGER = LogManager.getLogger();
public List<String[]> getSuggestListByItems(String codeSite) {
List<String[]> suggestList = new ArrayList<>();
String query = "SELECT iDcode, designation FROM Mytable WHERE codeSite = " + codeSite; // Simplified query building
DBAccess accesBD = new DBAccess();
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
conn = accesBD.getConnection();
stmt = conn.createStatement();
rs = stmt.executeQuery(query);
while (rs.next()) {
suggestList.add(new String[]{rs.getString(1), rs.getString(2)});
}
} catch (NamingException | SQLException ex) {
LOGGER.error("", ex);
} finally {
accesBD.closeResultSet(rs);
accesBD.closeStatement(stmt);
accesBD.closeConnection(conn);
}
return suggestList;
}
public String getDisplayValueByItems(String table, String codeSite) {
String displayValue = null;
String query = "SELECT iDcode, designation FROM " + table + " WHERE codeSite = " + codeSite; // Different query building
DBAccess accesBD = new DBAccess();
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
conn = accesBD.getConnection();
stmt = conn.createStatement();
rs = stmt.executeQuery(query);
if (rs.next()) {
displayValue = rs.getString(1);
}
} catch (NamingException | SQLException ex) {
LOGGER.error("", ex);
} finally {
accesBD.closeResultSet(rs);
accesBD.closeStatement(stmt);
accesBD.closeConnection(conn);
}
return displayValue;
}
public List<String[]> getSuggestListByListID(String listeID, String table, String codeSite) {
List<String[]> suggestList = new ArrayList<>();
String query = "SELECT iDcode, designation FROM " + table + " WHERE codeSite = " + codeSite; // Different query building involving listID
DBAccess accesBD = new DBAccess();
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
conn = accesBD.getConnection();
stmt = conn.createStatement();
rs = stmt.executeQuery(query);
while (rs.next()) {
suggestList.add(new String[]{rs.getString(1), rs.getString(2)});
}
} catch (NamingException | SQLException ex) {
LOGGER.error("", ex);
} finally {
accesBD.closeResultSet(rs);
accesBD.closeStatement(stmt);
accesBD.closeConnection(conn);
}
return suggestList;
}
public String getDisplayValueByListeID(String listeID, String table, String codeSite) {
String displayValue = null;
String query = "SELECT iDcode, designation FROM " + table + " WHERE codeSite = " + codeSite; // Different query building involving listID
DBAccess accesBD = new DBAccess();
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
conn = accesBD.getConnection();
stmt = conn.createStatement();
rs = stmt.executeQuery(query);
if (rs.next()) {
displayValue = rs.getString(2);
}
} catch (NamingException | SQLException ex) {
LOGGER.error("", ex);
} finally {
accesBD.closeResultSet(rs);
accesBD.closeStatement(stmt);
accesBD.closeConnection(conn);
}
return displayValue;
}
}
这是新的类（有泄漏的类）：
public class SqlSuggest {
private static final Logger LOGGER = LogManager.getLogger();
public List<String[]> getSuggestListByItems(String codeSite) {
List<String[]> suggestList;
String query = "SELECT iDcode, designation FROM Mytable WHERE codeSite = " + codeSite; // Simplified query building
suggestList = executeQueryGetListOfStringArray(query);
return suggestList;
}
public String getDisplayValueByItems(String table, String codeSite) {
String displayValue = null;
String query = "SELECT iDcode, designation FROM " + table + " WHERE codeSite = " + codeSite; // Different query building
int columnToFetch = 1;
displayValue = executeQueryGetString(query, columnToFetch);
return displayValue;
}
public List<String[]> getSuggestListByListID(String listeID, String table, String codeSite) {
List<String[]> suggestList = new ArrayList<>();
String query = "SELECT iDcode, designation FROM " + table + " WHERE codeSite = " + codeSite; // Different query building involving listID
suggestList = executeQueryGetListOfStringArray(query);
return suggestList;
}
public String getDisplayValueByListeID(String listeID, String table, String codeSite) {
String displayValue = null;
String query = "SELECT iDcode, designation FROM " + table + " WHERE codeSite = " + codeSite; // Different query building involving listID
int columnToFetch = 2;
displayValue = executeQueryGetString(query, columnToFetch);
return displayValue;
}
private String executeQueryGetString(String query, int columnToFetch){
String result = null;
Statement stmt = null;
Connection conn = null;
ResultSet rs = executeQuery(query, stmt, conn);
try{
if (rs.next()) {
result = rs.getString(columnToFetch);
}
} catch (SQLException ex) {
LOGGER.error("", ex);
} finally {
DBAccess accesBD = new DBAccess();
accesBD.closeResultSet(rs);
accesBD.closeStatement(stmt);
accesBD.closeConnection(conn);
}
return result;
}
private List<String[]> executeQueryGetListOfStringArray(String query){
List<String[]> result = new ArrayList<>();
Statement stmt = null;
Connection conn = null;
ResultSet rs = executeQuery(query, stmt, conn);
try{
while (rs.next()) {
result.add(new String[]{rs.getString(1), rs.getString(2)});
}
} catch (SQLException ex) {
LOGGER.error("", ex);
} finally {
DBAccess accesBD = new DBAccess();
accesBD.closeResultSet(rs);
accesBD.closeStatement(stmt);
accesBD.closeConnection(conn);
}
return result;
}
private ResultSet executeQuery(String query, Statement stmt, Connection conn){
DBAccess accesBD = new DBAccess();
ResultSet rs = null;
try {
conn = accesBD.getConnection();
stmt = conn.createStatement();
rs = stmt.executeQuery(query);
} catch (NamingException | SQLException ex) {
LOGGER.error("", ex);
}
return rs;
}
}
这里是实际打开和关闭连接的类（没有以任何方式改变）：
public class DBAccess {
private final static Logger LOGGER = LogManager.getLogger();
public void closeResultSet(ResultSet rs) {
if (rs != null) {
try {
rs.close();
} catch (Exception e) {
LOGGER.error("", e);
}
}
}
public void closeStatement(Statement stmt) {
if (stmt != null) {
try {
stmt.close();
} catch (Exception e) {
LOGGER.error("", e);
}
}
}
public void closeConnection(Connection conn) {
if (conn != null) {
try {
conn.close();
} catch (Exception e) {
LOGGER.error("", e);
}
}
}
public Connection getConnection() throws SQLException, NamingException {
Connection cnx = null;
PropertiesManager manager = PropertiesDelegate.getPropertiesManager();
String jndi = manager.getProperty("datasource.name", "QuartisWeb-PU");
Context ctx = null;
DataSource dataSource = null;
try {
ctx = new InitialContext();
dataSource = (DataSource) ctx.lookup(jndi);
} catch (NamingException ex) {
try {
dataSource = (DataSource) ctx.lookup("java:comp/env/" + jndi);
} catch (NamingException ex1) {
LOGGER.error("", ex1);
}
}
if (dataSource != null) {
cnx = dataSource.getConnection();
}
return cnx;
}
}
请忽略查询中未正确设置这些参数的事实，我知道应该这样做。
【问题讨论】：
-
我强烈推荐使用现有的框架（也许 Apache Commons Db 有像 'closeQuietly' 这样的方法以正确的顺序关闭你的语句、连接和结果集），或者 SpringJdbc，它封装了很多以上
-
是的，这就是我对下一个项目的想法。但是这个已经 10 年了，它正在生产中，我们有比修复工作更紧迫的事情。总有一天……
-
@BrianAgnew 或者使用try-with-resources，效果和`closeQuietly不完全一样，但更简洁。