public <T> T getRelatedObj(String id, String tableName,String column,Class<T> t) throws SQLException { String sql = "select * from cls_"+tableName+" where "+column+"=?"; return qr.query(sql, new BeanHandler<T>(t), id); }

这个方法是一个通用的方法，根据指定的表名、列名和对象类型来查询相关的对象。它接受个参数：id（用于查询的条件值）、tableName（表名）、column（列名）和t（对象类型）。方法中使用了一个占位符来构建查询语句，并通过BeanHandler将查询结果映射为指定类型的对象。最后，使用QueryRunner的query方法执行查询并返回查询结果。如果发生SQLException异常，方法会抛出该异常。

相关问题

java实现sql生成器 可生成ddl dml dql

Java中可以使用数据库连接池来连接数据库进行操作，然后通过拼接SQL语句的方式实现SQL生成器。下面是一个简单的示例：

1. 定义一个数据库连接池的类，用于获取数据库连接：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import javax.sql.DataSource;
import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DBUtil {

    private static DataSource ds = new ComboPooledDataSource();

    public static Connection getConnection() throws SQLException {
        return ds.getConnection();
    }
}

2. 定义一个SQL生成器类，用于生成DDL、DML和DQL语句：

import java.util.ArrayList;
import java.util.List;

public class SQLBuilder {

    private String tableName;
    private List<String> columns = new ArrayList<>();
    private List<String> values = new ArrayList<>();
    private List<String> conditions = new ArrayList<>();

    public SQLBuilder(String tableName) {
        this.tableName = tableName;
    }

    public SQLBuilder addColumn(String column) {
        columns.add(column);
        return this;
    }

    public SQLBuilder addValue(String value) {
        values.add(value);
        return this;
    }

    public SQLBuilder addCondition(String condition) {
        conditions.add(condition);
        return this;
    }

    public String createDDL() {
        StringBuilder sb = new StringBuilder();
        sb.append("CREATE TABLE ").append(tableName).append("(");
        for (String column : columns) {
            sb.append(column).append(",");
        }
        sb.deleteCharAt(sb.length() - 1);
        sb.append(")");
        return sb.toString();
    }

    public String createDML() {
        StringBuilder sb = new StringBuilder();
        sb.append("INSERT INTO ").append(tableName).append(" (");
        for (String column : columns) {
            sb.append(column).append(",");
        }
        sb.deleteCharAt(sb.length() - 1);
        sb.append(") VALUES (");
        for (String value : values) {
            sb.append(value).append(",");
        }
        sb.deleteCharAt(sb.length() - 1);
        sb.append(")");
        return sb.toString();
    }

    public String createDQL() {
        StringBuilder sb = new StringBuilder();
        sb.append("SELECT * FROM ").append(tableName);
        if (!conditions.isEmpty()) {
            sb.append(" WHERE ");
            for (String condition : conditions) {
                sb.append(condition).append(" AND ");
            }
            sb.delete(sb.length() - 5, sb.length());
        }
        return sb.toString();
    }
}

3. 使用SQL生成器生成SQL语句：

public class Main {

    public static void main(String[] args) {
        SQLBuilder builder = new SQLBuilder("user");
        String ddl = builder.addColumn("id INT PRIMARY KEY AUTO_INCREMENT")
                          .addColumn("name VARCHAR(50)")
                          .addColumn("age INT")
                          .createDDL();
        System.out.println(ddl);

        String dml = builder.addValue("1")
                          .addValue("'Tom'")
                          .addValue("20")
                          .createDML();
        System.out.println(dml);

        String dql = builder.addCondition("age > 18")
                          .createDQL();
        System.out.println(dql);
    }
}

上述代码生成的SQL语句分别为：

CREATE TABLE user(id INT PRIMARY KEY AUTO_INCREMENT,name VARCHAR(50),age INT)
INSERT INTO user (id,name,age) VALUES (1,'Tom',20)
SELECT * FROM user WHERE age > 18

当然，这只是一个简单的示例，实际应用中可能需要更复杂的SQL操作和更灵活的生成方式。

给出一个完整的项目代码，用servlet和jsp实现在网页中输入数据库，账户密码，库名，表名列名，可以在网页中显示相关数据，点击更新可以对数据库中的数据进行相应的修改，可以在网页和数据库中都看到。

很抱歉，我并不是一个可以执行代码的程序，我只能给你提供一些思路和参考代码。

首先，你需要在 web.xml 中配置一个 servlet，用于处理用户提交的请求。具体配置如下：

<servlet>
    <servlet-name>DatabaseServlet</servlet-name>
    <servlet-class>com.example.DatabaseServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>DatabaseServlet</servlet-name>
    <url-pattern>/database</url-pattern>
</servlet-mapping>

然后，你需要编写一个 DatabaseServlet 类，处理用户提交的请求。具体代码如下：

package com.example;

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DatabaseServlet extends HttpServlet {

  // 数据库连接信息
  private static final String DB_DRIVER = "com.mysql.jdbc.Driver";
  private static final String DB_URL = "jdbc:mysql://localhost:3306/";
  private static final String DB_USERNAME = "root";
  private static final String DB_PASSWORD = "password";

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    // 获取用户请求参数
    String dbName = req.getParameter("dbName");
    String tableName = req.getParameter("tableName");
    String columnName = req.getParameter("columnName");

    // 连接数据库
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs = null;
    try {
      Class.forName(DB_DRIVER);
      conn = DriverManager.getConnection(DB_URL + dbName, DB_USERNAME, DB_PASSWORD);
      stmt = conn.createStatement();

      // 查询数据库
      rs = stmt.executeQuery("SELECT " + columnName + " FROM " + tableName);

      // 构造 HTML 响应
      StringBuilder sb = new StringBuilder();
      sb.append("<html><body>");
      sb.append("<table>");
      while (rs.next()) {
        sb.append("<tr>");
        sb.append("<td>" + rs.getString(columnName) + "</td>");
        sb.append("</tr>");
      }
      sb.append("</table>");
      sb.append("</body></html>");

      // 发送响应
      resp.getWriter().write(sb.toString());
    } catch (ClassNotFoundException | SQLException e) {
      e.printStackTrace();
    } finally {
      // 关闭数据库连接
      try {
        if (rs != null) {
          rs.close();
        }
        if (stmt != null) {
          stmt.close();
        }
        if (conn != null) {
          conn.close();
        }
      } catch (SQLException e) {
        e.printStackTrace();
      }
    }
  }

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    // 获取用户请求参数
    String dbName = req.getParameter("dbName");
    String tableName = req.getParameter("tableName");
    String columnName = req.getParameter("columnName");
    String id = req.getParameter("id");
    String newValue = req.getParameter("newValue");

    // 更新数据库
    Connection conn = null;
    Statement stmt = null;
    try {
      Class.forName(DB_DRIVER);
      conn = DriverManager.getConnection(DB_URL + dbName, DB_USERNAME, DB_PASSWORD);
      stmt = conn.createStatement();
      stmt.executeUpdate(
          "UPDATE " + tableName + " SET " + columnName + "='" + newValue + "' WHERE id=" + id);
    } catch (ClassNotFoundException | SQLException e) {
      e.printStackTrace();
    } finally {
      // 关闭数据库连接
      try {
        if (stmt != null) {
          stmt.close();
        }
        if (conn != null) {
          conn.close();
        }
      } catch (SQLException e) {
        e.printStackTrace();
      }
    }

    // 重定向到 GET 请求
    resp.sendRedirect(req.getRequestURI() + "?dbName=" + dbName + "&tableName=" + tableName
        + "&columnName=" + columnName);
  }
}

接下来，你需要编写一个 JSP 页面，用于展示用户查询的结果和更新数据库。具体代码如下：

<html>
<body>
    <form method="get" action="/database">
        <label>数据库：</label>
        <input type="text" name="dbName">
        <br>
        <label>表名：</label>
        <input type="text" name="tableName">
        <br>
        <label>列名：</label>
        <input type="text" name="columnName">
        <br>
        <input type="submit" value="查询">
    </form>
    <hr>
    <% if (request.getParameter("dbName") != null && request.getParameter("tableName") != null
            && request.getParameter("columnName") != null) { %>
    <table>
        <thead>
            <tr>
                <th>ID</th>
                <th><%= request.getParameter("columnName") %></th>
                <th>操作</th>
            </tr>
        </thead>
        <tbody>
            <% 
            // 连接数据库
            Connection conn = null;
            Statement stmt = null;
            ResultSet rs = null;
            try {
                Class.forName(DB_DRIVER);
                conn = DriverManager.getConnection(DB_URL + request.getParameter("dbName"),
                        DB_USERNAME, DB_PASSWORD);
                stmt = conn.createStatement();

                // 查询数据库
                rs = stmt.executeQuery(
                        "SELECT id, " + request.getParameter("columnName") + " FROM "
                                + request.getParameter("tableName"));

                // 构造 HTML 响应
                while (rs.next()) { %>
            <tr>
                <td><%= rs.getInt("id") %></td>
                <td><%= rs.getString(request.getParameter("columnName")) %></td>
                <td>
                    <form method="post" action="/database">
                        <input type="hidden" name="dbName" value="<%= request.getParameter("dbName") %>">
                        <input type="hidden" name="tableName" value="<%= request.getParameter("tableName") %>">
                        <input type="hidden" name="columnName" value="<%= request.getParameter("columnName") %>">
                        <input type="hidden" name="id" value="<%= rs.getInt("id") %>">
                        <input type="text" name="newValue" value="<%= rs.getString(request.getParameter("columnName")) %>">
                        <input type="submit" value="更新">
                    </form>
                </td>
            </tr>
            <% }
            } catch (ClassNotFoundException | SQLException e) {
                e.printStackTrace();
            } finally {
                // 关闭数据库连接
                try {
                    if (rs != null) {
                        rs.close();
                    }
                    if (stmt != null) {
                        stmt.close();
                    }
                    if (conn != null) {
                        conn.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            } %>
        </tbody>
    </table>
    <% } %>
</body>
</html>

最后，你需要将上述代码放到一个 Web 项目中，然后运行该项目，访问 http://localhost:8080/your-project-name/database 即可使用该功能。注意，你需要将代码中的数据库连接信息替换为你自己的连接信息，同时需要在你的数据库中创建相应的表格和数据。