纯Java JDBC连接数据库，且用JDBC实现增删改查的功能

Java JDBC连接数据库

package cn.cqvie.yjq;

import java.sql.*;

/**
 * 注册数据库的驱动程序，并得到数据库的连接对象
 * @author yu
 *
 */

public class DBUtil {

    static String DriverName = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
    static String URL = "jdbc:sqlserver://localhost:1433;DatabaseName=book";
    static String USER = "sa";
    static String PASSWORD = "123";

    //静态代码块，只执行一次
    static {
        try {
            Class.forName(DriverName);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    //得到连接对象
    public static Connection getConnection() {
        Connection conn = null;
        try {
            conn = DriverManager.getConnection(URL,USER,PASSWORD);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }

    //关闭连接
    public static void free(ResultSet rs,Statement stmt, Connection conn) {
        if(rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                if(stmt != null) {
                    try {
                        stmt.close();
                    } catch (Exception e2) {
                        e2.printStackTrace();
                    } finally {
                        if(conn != null) {
                            try {
                                conn.close();
                            } catch (Exception e3) {
                                e3.printStackTrace();
                            }
                        }
                    }
                }
            }
        }
        /*
        if(stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                if(stmt != null) {
                    try {
                        stmt.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
            }
        }

        if(conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
        */
    }
}

使用JDBC实现增删改查的功能

package cn.cqvie.yjq;

import java.sql.*;
import java.util.*;

public class SQLHelper {

    /**
     * 根据Connection，带坑语句，所有坑的值params来生成一个具体的PreparedStatement语句
     * @param conn
     * @param cmdText
     * @param params
     * @return
     * @throws SQLException
     */

    public static PreparedStatement getPreparedStatement(Connection conn,String cmdText,Object... params) {
        if(conn == null) {
            return null;
        }
        PreparedStatement pstmt = null;
        try {
            pstmt = conn.prepareStatement(cmdText);
            int i = 1;
            if(params != null) {
                for(Object obj:params) {
                    if(obj != null) {
                        pstmt.setObject(i, obj);
                    }
                    i ++;
                }
            }
            //DBUtil.free(null, null, conn);
            return pstmt;
        } catch (SQLException e) {
            e.printStackTrace();
            DBUtil.free(null, pstmt, conn);
        }
        return null;
    }

    /**
     * 查询一个结果集
     * @param conn
     * @param cmdText
     * @param params
     * @return
     * @throws SQLException
     */
    public static List<Object[]> executeQuery(Connection conn,String cmdText,Object...params) {
        PreparedStatement pstmt = getPreparedStatement(conn, cmdText, params);
        ResultSet rs = null;
        List<Object[]> list = new ArrayList<Object[]>();
        try {
            rs = pstmt.executeQuery();
            //从rs中获取每一个行数据的列的个数
            ResultSetMetaData rsmd = rs.getMetaData();
            int columnCount = rsmd.getColumnCount();
            //定义一个保存每一行的各个列的值的容器，Object[]
            Object[] objects = null;
            while(rs.next()) {
                objects = new Object[columnCount];
                for(int i = 0;i < columnCount;i ++) {
                    objects[i] = rs.getObject(i + 1);
                }
                list.add(objects);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.free(rs, pstmt, conn);
        }
        return list;
    }

    /**
     * 查询一个具体的值
     * @param conn
     * @param cmdText
     * @param params
     * @return
     * @throws SQLException
     */
    public static Object executeScalar(Connection conn,String cmdText,Object...params) {
        Object obj = null;
        if(conn == null) {
            return null;
        }
        List<Object[]> list = executeQuery(conn, cmdText, params);
        if(list != null && list.size() != 0) {
            obj = list.get(0)[0];
            return obj;
        }
        return null;
    }

    /**
     * 增删改方法
     * @param conn
     * @param cmdText
     * @param params
     * @return
     * @throws SQLException
     */
    public static int executeUpdate(Connection conn,String cmdText,Object...params) {
        if(conn == null) {
            return -2;
        }
        PreparedStatement pstmt = getPreparedStatement(conn, cmdText, params);
        int rows = 0;
        try {
            rows = pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.free(null, pstmt, conn);
        }
        return rows;
    }
}