JDBC入门学习

JDBC学习

JAVA Database Connectivity java 数据库连接

• 为什么会出现JDBC

SUN公司提供的一种数据库访问规则、规范, 由于数据库种类较多，并且java语言使用比较广泛，sun公司就提供了一种规范，让其他的数据库提供商去实现底层的访问规则。 我们的java程序只要使用sun公司提供的jdbc驱动即可。

JDBC的步骤

1. load the driver

   此时的意思是向DriverManager注册驱动

    try {
        Class.forName(driverClass);
    }
    catch(ClassNotFoundException e) {
        e.printStackTrace();
    }
   

   forName() throws ClassNotFoundException

   driverClass为相应的驱动类 eg:Oracle.jdbc.driver.OracleDriver

2. connect to database

    try {
        conn = DriverManager.getConnection(url,user,password);
    }
    catch(SQLException e) {
        e.printStackTrace();
    }
   

   getConnection()方法抛出SQLException

3. execute sql statement

    Statement stmt = null;
    
    stmt = conn.createStatement();
        
    String sql = "select * from dept";
    rs = stmt.executeQuery(sql);
   

4. retrieve the data

    int deptno = 0;
    String dname = null;
    String loc = null;
        
    while(rs.next()) {
        deptno = rs.getInt("deptno");
        dname = rs.getString("dname");
        loc = rs.getString("loc");
        System.out.println("deptno = " + deptno +"  dname = " + dname + " loc = " + loc);
    }
   

5. close the resource

    rs.close();
    stmt.close();
    conn.close();
   

6. 程序整体

    public static void main(String[] args) {
        Connection connection = null;
        Statement statement = null;
        ResultSet result = null;
        
        try {
            //注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            
            //建立连接
            connection = DriverManager.getConnection("jdbc:mysql://localhost/student", "root", "root");
            
            //创建语句
            statement = connection.createStatement();
            
            //执行查询，得到结果集
            String sql = "select * from t_stu";
            result = statement.executeQuery(sql);
            
            //遍历结果集
            while(result.next()) {
                int id = result.getInt("id");
                String name = result.getString("name");
                int age = result.getInt("age");
                
                System.out.println("id = " + id + " name = " + name + " age = " + age);          
            }
        }catch(ClassNotFoundException e) {
            e.printStackTrace();
        } catch(SQLException e) {
            e.printStackTrace();
        } finally {
            JDBCUtil.closeResource(connection, statement, result);
        }           
    }
   

JDBC工具类的创建

因为有关JDBC的操作中经常性的会用到以上步骤，所以最好是写入包装类，等到使用时直接添加即可

工具类名称:JDBCUtil

1. 配置文件的生成--new file--jdbc.properties

   需要的类有：java.util.Properities

   driverClass = com.mysql.jdbc.Driver
   url = jdbc:mysql://localhost/student
   user = root
   password = root
   

2. 配置文件的使用

   static中使用

   static {
   //创建属性配置对象
   Properties properties = new Properties();

   //使用类加载器，读取src底下的资源文件
   InputStream iStream = JDBCUtil.class.getClassLoader().getResourceAsStream("jdbc.properties");
       
   //导入输入流:
   try {
       properties.load(iStream);
   } catch (IOException e) {
       // TODO Auto-generated catch block
       e.printStackTrace();
   }
   
   //读取属性
   driverClass = properties.getProperty("driverClass");
   url = properties.getProperty(url);
   name = properties.getProperty(name);
   password = properties.getProperty(password);
   

   }

3. 将 load the driver 和 Connect to database 合并为getConne()方法

    public static Connection getConn() {
        Connection conn = null;
    
        //--load the driver
        try {
            Class.forName(driverClass);
        }
        catch(ClassNotFoundException e) {
            e.printStackTrace();
        }
        
        //--connect to database;
    
        try {
            conn = DriverManager.getConnection(url,user,password);
        }
        catch(SQLException e) {
            e.printStackTrace();
        }
        
        return conn;
}   

4. 添加closeResource()方法

   主程序中finally中之执行closeResource()方法，进行资源释放

   public static void closeResource(ResultSet rs,Statement stmt,Connection conn){
       closeRs(rs);
       closeStmt(stmt);
       closeConn(conn);
   }
   
   public static void closeResource(PreparedStatement pstmt,Connection conn){
       closeStmt(pstmt);  //preparedStatement是statement的一个子类
       closeConn(conn);
   

   }

   static void closeRs(ResultSet rs) {
       try {
           if(rs != null)
               rs.close();         
       }
       catch(SQLException e) {
           e.printStackTrace();
       }
       finally {
           rs = null;
       }
   }
   
   static void closeStmt(Statement stmt) {
       try {
           if(stmt != null)
               stmt.close();
       }
       catch(SQLException e) {
           e.printStackTrace();
       }
       finally {
           stmt = null;
       }
   }
   
   static void closeConn(Connection conn) {
       try {
           if(conn != null)
               conn.close();
       }
       catch(SQLException e) {
           e.printStackTrace();
       }
       finally {
           conn = null;
       }
   }
   

   此时注意方法的重载

JDBC的DML使用

1. 预备知识

   JUnit的使用：

   ①添加Junit的lib

   ②new Junit Test Case

---

2. testQuery()
   --测试查询

    public void testQuery() {
        Connection conn = JDBCUtil.getConn();       
        Statement stmt = null;
        ResultSet rs = null;
    
        
        try {
            //execute sql statement
            stmt = conn.createStatement();
            
            String sql = "select * from dept";
            rs = stmt.executeQuery(sql);
   
            /*
                注意:executeQuery()返回的是ResultSet
             */
            
            
            //retrieve the data             
            int deptno = 0;
            String dname = null;
            String loc = null;
            
            while(rs.next()) {
                deptno = rs.getInt("deptno");
                dname = rs.getString("dname");
                loc = rs.getString("loc");
                System.out.println("deptno = " + deptno +"  dname = " + dname + " loc = " + loc);
            }
            
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //close the resource
            JDBCUtil.closeResource(rs, stmt, conn);
        }       
    }
   

3. testInsert()

    public void testInsert() {
        Connection conn = JDBCUtil.getConn();       
        Statement stmt = null;
   
        try {
            //execute sql statement
            stmt = conn.createStatement();
            
            String sql = "insert into dept values(50,'What','Shanxi')";
            int result = stmt.executeUpdate(sql);
            
            if(result == 0) {
                System.out.println("添加失败");
            }
            else {
                System.out.println("添加成功");
            }
        }catch(SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtil.closeResource(stmt, conn);
        }
    }
   

4. testInsert_2()--使用preparedStatement

    public void testInsert_2() {
        Connection conn = JDBCUtil.getConn();       
        PreparedStatement prestmt = null;
   
        try {
            //execute sql statement
            prestmt = conn.prepareStatement("insert into dept values(?,?,?)");
            prestmt.setInt(1, 55);
            prestmt.setString(2,"hahahaha");
            prestmt.setString(3, "henan");
            int result = prestmt.executeUpdate();   
            
            if(result == 0) {
                System.out.println("添加失败");
            }
            else {
                System.out.println("添加成功");
            }
            
        }catch(SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtil.closeResource(prestmt, conn);   //此时运用到多态
        }
    }   
   

5. testDelete()

   public void testDelete() {
       Connection conn = JDBCUtil.getConn();       
       Statement stmt = null;
   
       try {
           //execute sql statement
           stmt = conn.createStatement();
           
           String sql = "delete from dept where deptno = 55";
           int result = stmt.executeUpdate(sql);
           
           if(result == 0) {
               System.out.println("删除失败");
           }
           else {
               System.out.println("删除成功");
           }
       }catch(SQLException e) {
           e.printStackTrace();
       }finally {
           JDBCUtil.closeResource(stmt, conn);
       }
   }
   

6. testUpdate()

    @Test
    public void testUpdate() {
        Connection conn = JDBCUtil.getConn();       
        Statement stmt = null;
   
        try {
            //execute sql statement
            stmt = conn.createStatement();
            
            String sql = "update dept set dname = 'xixixixi' where deptno = 55";
            int result = stmt.executeUpdate(sql);
            
            if(result == 0) {
                System.out.println("更新失败");
            }
            else {
                System.out.println("更新成功");
            }
        }catch(SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtil.closeResource(stmt, conn);
        }
    }
   

DAO模式

Data Access Object 访问数据对象

可以实现业务逻辑与数据库访问相分离

---

一般的DAO的封装由以下另个原则：

1. 一个表对应一个dao接口，对应一个相应实现类。

2. 对于DAO接口，必须由具体的类型定义。这样可以避免被错误地调用

---

一般步骤

1. 创建相关表的接口--new Interface--DeptDao--此时例子是对dept表进行操作

   里面封装相应对于此表的操作：eg: query,delete,update,insert

    package com.anna.dao;
   
    public interface DeptDao {
        //查询所有
        public void findAll();  
    }
   

2. 创建接口的实现类--一般与接口在不同包中

   ----继承接口

   ----实现接口中的抽象方法

    public class DeptDaoImpl implements DeptDao{
    
        public void findAll() {
   
            //Connect to database
            Connection conn = JDBCUtil.getConn();
            
            //execute sql statement
            Statement stmt= null;
            ResultSet rs = null;
            
            try {
                 stmt = conn.createStatement();
                 
                 String sql = "select * from dept";
                 rs = stmt.executeQuery(sql);
                 
                 while(rs.next()) {
                     int deptno = rs.getInt("deptno");
                     String dname = rs.getString("dname");
                     String loc = rs.getString("loc");
                     
                     System.out.println("deptno = " + deptno + "  dname = " + dname + "  loc = " + loc + "\n");
                 }
            }
            catch(SQLException e) {
                e.printStackTrace();
            }finally {
                JDBCUtil.closeResource(stmt,conn);
            }
        }
    }
   

3. 利用JUnit测试相关方法

    public class TestDeptDaoImpl {
        
        @Test
        public void testFindAll() {
            DeptDao dd = new DeptDaoImpl();   //接口引用指向实现类
            dd.findAll();
        }
    }
   

Statement的安全问题

1. Statement执行 ，拼接sql语句的。 先拼接sql语句，然后在一起执行。

   ---此时可能会导致错误

PreparedStatement的学习

由于statement本身存在的问题，引出了PreparedStatement

//execute sql statement
    PreparedStatement pstmt= null;      
    ResultSet rs = null;
    
    try {
         String sql = "select * from dept where deptno = ? and dname = ? and loc = ?"; 
         pstmt = conn.prepareStatement(sql);
         pstmt.setInt(1, deptno);
         pstmt.setString(2,dname);
         pstmt.setString(3,loc);
         
         rs = pstmt.executeQuery();          
         if(rs.next()) {
             System.out.println("验证成功");
         }
         else {
             System.out.println("验证失败");
         }
    }
    catch(SQLException e) {
        e.printStackTrace();
    }finally {
        JDBCUtil.closeResource(pstmt,conn);
    }

总结

1. JDBC的学习

2. JDBC工具类的创建

3. JDBC的DML的实现

4. DAO模式的了解

5. PreparedStatement的学习