java - PreparedStatement 和 ResultSet 上的资源泄漏

Question

Eclipse 显示警告消息“资源泄漏，准备好的语句未在以下位置关闭”

对我来说，finally block 似乎负责关闭准备好的语句和 rs 对象。知道为什么 eclipse 仍然提示资源泄漏吗？

String ruleGrpId = null;
        int finalRuleID = 0;

        String saveRule1 = "INSERT INTO ..";
        String saveRule2 = "INSERT INTO ";

        String saveRule3 = "select ..._name = ?";

        PreparedStatement preparedstatement = null;
        ResultSet rs = null;

        try {
            if (objSomeRule.getRule() == 0) {

                preparedstatement = con.prepareStatement(saveRule1);
                preparedstatement.setString(1, ruleId);

                preparedstatement.executeUpdate();

                //Eclipse complains here
                preparedstatement = con.prepareStatement(saveRule2);

                preparedstatement.setInt(1, ruleID_2);
                preparedstatement.setString(2, ruleID_3);

                rs =  preparedstatement.executeQuery();

                if(rs.next()){
                    finalRuleID = rs.getInt(1);
                }else{
                    //complains here
                    preparedstatement = con.prepareStatement(saveRule3);
                    preparedstatement.setString(1, ruleID_4);
                    //complains here
                    rs =  preparedstatement.executeQuery();
                    if(rs.next()){
                        finalRuleID = rs.getInt("rulegroup_id");
                    }
                }
                objSomeRule.setRuleID(finalRuleID);

            }

        } finally {

            if(preparedstatement != null){
                preparedstatement.close();
            }

            if(rs != null){
                rs.close();
            }
        }

        return finalRuleID;
    }

Answer 1

重用变量preparedStatement和rs可以防止对变量的旧对象值调用close()。 Try-with-resources 是一个巧妙的解决方案，因为即使抛出异常或在深度嵌套的 try 中执行返回，也会自动调用 close()。

    String ruleGrpId = null;
    int finalRuleID = 0;
    String saveRule1 = "INSERT INTO ..";
    String saveRule2 = "INSERT INTO ";
    String saveRule3 = "select ..._name = ?";

    if (objSomeRule.getRule() == 0) {
        try (PreparedStatement ps1 = con.prepareStatement(saveRule1)) {
            ps1.setString(1, ruleId);
            ps1.executeUpdate();
        }
        try (PreparedStatement ps2 = con.prepareStatement(saveRule2)) {
            ps2.setInt(1, ruleID_2);
            ps2.setString(2, ruleID_3);

            try (ResultSet rs2 =  ps2.executeQuery()) {

                if (rs2.next()) {
                    finalRuleID = rs2.getInt(1);
                } else {
                    try (Preparedstatement ps3 = con.prepareStatement(saveRule3)) {
                        ps3.setString(1, ruleID_4);
                        //complains here
                        try (ResultSet rs3 =  ps3.executeQuery()) {
                            if (rs3.next()) {
                                finalRuleID = rs3.getInt("rulegroup_id");
                            }
                        }
                    }
                }
            }
            objSomeRule.setRuleID(finalRuleID);
        }
    }

如果最后一个 SELECT 查询打算检索先前 INSERT 的 AUTOINCRMENT ID，则可以使用 getGeneratedKeys 更安全(多用户)和更好地完成此操作。