数据库连接泄漏

Question

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使用对System.nanoTime（）的调用来环绕查询。 在这样做时，我发现了一个类（SqlSuggest），它包含4种非常相似的方法，包含4个非常相似的方法。我认为重构和重新组合公共部分是个好主意。

这造成连接泄漏，连接不再关闭。我回滚了重构，但我还是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Connection，Statement和ResultSet（在finally块中）：DBAccess。

该类的第二个版本具有相同的4个方法，除了不打开和关闭Connection，它们根据是否需要一个结果或列表来调用2个方法中的1个。

这两个方法（executeQueryGetString和executeQueryGetListOfStringArray）分别声明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。

第二层方法然后从ResultSet中提取数据并关闭所有内容。

我猜我错误地认为在方法中声明Connection，Statement和ResultSet会允许我从同一个方法中关闭它们。

这是旧类（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;
    }
}

这是新类（具有泄漏的类）：

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;
    }
}

这是实际打开和关闭连接的类（它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;
    }

}

请忽略这些参数未在查询中正确设置的事实，我知道应该这样做。

Answer 1

当您从executeQueryGetString()拨打executeQuery()时，conn和stmt的值将在executeQuery()内更改，但仍会null返回时在executeQueryGetString()内。因此，在finally的{​​{1}}，对executeQueryGetString()的调用实际上是accesBD.closeConnection(conn)