Jdbc 使用 java 连接

Question

I have Rest-Api in the java.

That will take dbUrl, dbUserName, dbPassWord, dbDriver and sql query

and gives me the result set and after I will be converting into json format.

Class.forName("oracle.jdbc.driver.OracleDriver");
connectionUrl = "jdbc:oracle:thin:@" + server + ":" + dbName + "";
conn = DriverManager.getConnection(connectionUrl, userName, password);
try {
    stmt = conn.createStatement();
    output = resultSetHandler(stmt.executeQuery(query)); // this method convert ResultSet to Json
    } catch (SQLException e) {
        throw new Error(e);
    } finally {
        if (stmt != null) {
            stmt.close();
        }
    }
} catch (SQLException e) {
    throw new Error(e);
} finally {
    try {
        if (conn != null) {
            conn.close();
        }
    } catch (SQLException ex) {
        throw new Error(ex);
    }
}

The problem here is that When 30 users use this api at one time means It will throw an error for few users.... and also I will not be using just oracle and I will be using postgres, mysql also

Answer 1

1. Consider using DB connection pool such as Hikari or C3P0 (both available at Maven Repository). Opening a connection every time is very inefficient and you may run out of connections which may be the error you are getting. Please post your error.
2. Use try-with-resources instead of doing the finally block. It will automatically call close() on Autoclosable objects such as Connection, Statement, PreparedStatement, ResultSet, etc.

 try ( Connection myConnection = MyConnectionPool.getConnection(); Statement stmt = myConnection.createStatement(); ResultSet rs = stmt.executeQuery(query) ) { // Do work with rs }