java - 将 Hashmap 数据移至数据库

Question

我有

  public HashMap<Integer, String> data;

  private void initData() {
    data= new HashMap<Integer, String>();
    data.put(1, "One");
    data.put(2, "Two");
    data.put(3, "Three");
    data.put(4, "Four");
    data.put(5, "Five");
    }

但是数据不断增加，所以我想将这个 HashMap 移到数据库中，所以每当我添加新的键值对时；我可以将它添加到数据库而不是接触java代码。

如何做到这一点？创建表， hibernate ，连接它......但对创建表和数据库调用感到困惑

Answer 1

数据库连接器

JDBC DRIVER

    import java.sql.*;

    public class Database {
      private static final String JDBC_DRIVER = "org.postgresql.Driver";
      private static final String URL = "jdbc:postgresql://localhost/testdb";
      private static final String USERNAME = "root";
      private static final String PASSWORD = "pass";

      private static Connection conn = null;

      public Database() {
       try {
         Class.forName(JDBC_DRIVER);
         conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
       } catch (Exception ex) {
          ex.printStackTrace();
       }
       System.out.println("Database Connection Initialized.");
     }

     public void closeConnection() {
       if (conn == null) return;
       try {
       conn.close();
       conn = null;
       } catch(SQLException ex) {
          ex.printStackTrace();
       }
     }

     public boolean execute(String sql) throws SQLException {
       if (conn == null)
          throw new SQLException("Connection null!");
       Statement statement = conn.createStatement();
       boolean res = statement.execute(sql);
       statement.close();
       return res;
    }

   public int executeUpdate(String sql) throws SQLException {
       if (conn == null)
          throw new SQLException("Connection null!");
       Statement statement = conn.createStatement();
       int res = statement.executeUpdate(sql);
       statement.close();
       return res;
    }

    public ResultSet executeQuery(String sql) throws SQLException {
       if (conn == null)
          throw new SQLException("Connection null!");
       Statement statement = conn.createStatement();
       ResultSet res = statement.executeQuery(sql);
       statement.close();
       return res;
    }
 }

创建表

    Database db = new Database();

    String sql = "CREATE TABLE IF NOT EXISTS `table` ("+
    "`key` INT(6) PRIMARY KEY,"+
    "`value` VARCHAR(50) NOT NULL"+
    ");";

    db.execute(sql);
    db.closeConnection();

将数据放入数据库

Database db = new Database();

for (Entry<Integer, String> next : hashMap) {
  db.executeUpdate("INSERT INTO table (Key, Value) VALUES("+next.getKey()+",'"+next.getValue()+"');";
}
db.closeConnection();

从数据库中提取数据

Database db = new Database();

ResultSet resSet = db.executeQuery("SELECT * FROM table");

while (resSet.next()) {
  hashMap.put(resSet.getInt("Key"), resSet.getString("Value"));
}

resSet.close();
db.closeConnection();