Question

此处代码的目的是通过选择列来读取记录。

我在SQL DB中有以下列。

------------------------------
|id | Topic | Comment | Time |
------------------------------

我想做的是： -

阅读数据库
能够按主题选择行
按主题显示或返回所选行的值

主题可以重复，但是在选择过程中不应该看到重复的值，但应检索所有列的值（以及重复的值）。

public class ReadRecordTopic{
       // JDBC driver name and database URL
       static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
       static final String DB_URL = "jdbc:mysql://localhost:3306/STUDENTS?user=root&password=";

       //  Database credentials
       //static final String USER = "username";
       //static final String PASS = "password";

       public static void main(String[] args) {

           Connection conn = null;
           Statement stmt = null;

           try{
          //STEP 2: Register JDBC driver
          Class.forName("com.mysql.jdbc.Driver");

          //STEP 3: Open a connection
          System.out.println("Connecting to a selected database...");
          conn = DriverManager.getConnection(DB_URL);
          System.out.println("Connected database successfully...");

          //STEP 4: Execute a query
          System.out.println("Creating statement..." + "\n");
          stmt = conn.createStatement();

          String sql = "SELECT id, Topic, Comment, Time FROM Registration";
          ResultSet rs = stmt.executeQuery(sql);

          //STEP 5: Extract data from result set
          while(rs.next()){
             //Retrieve by column name
             int id  = rs.getInt("id");
             String Topic = (String) rs.getString("Topic");
             String Comment = rs.getString("Comment");
             String Time = rs.getString("Time");

              String menu [] = Topic.split(",");
              Object[] selectionValues = menu;
              String initialSelection = "";

              Object selection = JOptionPane.showInputDialog(null,
                            "Please select the Topic.", "Reseach Forum Menu",
                            JOptionPane.QUESTION_MESSAGE, null, selectionValues,
                            initialSelection);

             String a = "Research Topic: " + Topic + "\n";
             String b = "[" + Time + "]" + " Comment:" + Comment + "\n";

             if(selection == Topic){JOptionPane.showMessageDialog(null, a + b);
             }     
        }

          rs.close();
       }catch(SQLException se){
          //Handle errors for JDBC
          se.printStackTrace();
       }catch(Exception e){
          //Handle errors for Class.forName
          e.printStackTrace();
       }finally{
          //finally block used to close resources
          try{
             if(stmt!=null)
                conn.close();
          }catch(SQLException se){
          }// do nothing
          try{
             if(conn!=null)
                conn.close();
          }catch(SQLException se){
             se.printStackTrace();
          }//end finally try
       }//end try
       System.out.println("Goodbye!");
    }//end main
    }//end JDBCExample

Answer 1

1-创建Registration.class

public class Registration{
private int id;
private String topic;
...
...
...
//getters and setters 
}

2-更改您的sql和函数名称以了解您想要的内容并使用它。

//for order topic
String sql = SELECT id, Topic, Comment, Time FROM Registration order by topic.

//function for just spesific topic

public class ArrayList<Registration> getRegisWithTopic(String topicName){
String sql = SELECT id, Topic, Comment, Time FROM Registration order by topic WHERE TOpic = topicName ;
}

3- in in create new Registration.class并添加到ArrayList并返回此列表

ArrayList<Registration> newList = new ArrayList<Registration>();

while(rs.next()){
             Registration newReg = new Registration();
             //Retrieve by column name
             newReg.setId(rs.getInt("id"));
             newReg.setTopic(rs.getString("Topic"));
...
...
...
             //add this obj to list
             newList.add(newReg);
}


return newList ;

JDBC - 将Resultset检索到列表中

1 个答案: