JDBC连接数据库重要点和示例

JDBC连接数据库重要点和示例

JDBC

java database connectivity java 与数据库的连接

服务器 (db)：

• 1.接收 sql
• 2.执行 sql
• 3.返回结果

客户端 (java)：

• 1.接收数据

• 2.组装sql

• 3.发送SQL(与数据库建立联系)

• 4.分析结果

示例：

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 java.util.Properties;

/**
 * 
 * 优化：
 * 	1.异常捕获
 * 	2.数据的配置信息使用配置文件动态读取
 * @author zhuch
 *
 */
public class JDBCSimpleDemo02 {
	public static void main(String[] args){
		Properties pro = new Properties();
		try {
			pro.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("db.properties"));
			
			 //1.加载驱动（选择哪一个数据库）
			 Class.forName(pro.getProperty("driver"));
		} catch (ClassNotFoundException | IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		 //2.获取连接（与数据库连接上）
		 Connection conn=null;
		 Statement state=null;
		 ResultSet result=null;
		try {
			conn = DriverManager.getConnection(
					 pro.getProperty("url"),
					 pro.getProperty("name"),
					 pro.getProperty("pwd"));
			//3.准备sql
			 String sql="select empno,ename from emp";//注意sql语句后面不要添加分号
			 //4.获取处理块（打包发送）
			 state = conn.createStatement();
			 //5.执行完毕得到结束，接收结果集
			 result = state.executeQuery(sql);
			 //6.处理数据
			 while(result.next()){
				int i= result.getInt("empno");
				String name = result.getString("ename");
				System.out.println(i+"-->"+name);
			 }
			
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally{
			
			 //7.关闭
			 try {
				 if(result!=null){
					result.close();
				 }
				 if(state!=null){
					state.close();
				 }
				 if(conn!=null){
					conn.close();
				 }
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		} 
	}
}

JDBC工具类

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 java.util.Properties;

/**
 * jdbc	工具类
 * 1.加载驱动
 * 2.获取连接
 * 3.关闭
 * @author zhuch
 *
 */
public class DBUtils {
	private static Properties pro = new Properties();
	//类第一次加载完之后只执行一次（加载驱动）
	static{
		try {
			pro.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("db.properties"));
			
			 //1.加载驱动（选择哪一个数据库）
			 Class.forName(pro.getProperty("driver"));
		} catch (ClassNotFoundException | IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	//获取连接
	public static Connection getConnection() throws SQLException{
		Connection conn=null;
		conn = DriverManager.getConnection(
				 pro.getProperty("url"),
				 pro.getProperty("name"),
				 pro.getProperty("pwd"));
			
		return conn;
	}
	//关闭
	public static void close(ResultSet result,Statement state,Connection conn){
		
		 //7.关闭
		 try {
			 if(result!=null){
				result.close();
			 }
			 if(state!=null){
				state.close();
			 }
			 if(conn!=null){
				conn.close();
			 }
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		 
	}
}

手动提交事务

示例：

    /*
	 * 模拟转账(方法)
	 */
	public static void test(){
		Connection conn=null;
		PreparedStatement state=null;
		
		try {
			//获取连接
			conn=DBUtils.getConnection();
			//设置手动提交
			conn.setAutoCommit(false);
			//2.sql
			String sql="update hehe set money=money-100 where name='lisi'";
			//3.预处理块
			state = conn.prepareStatement(sql);
			//4.执行sql，获取结果
			int row = state.executeUpdate();
			System.out.println(row);
			//sql2
			String sql2="update hehe set money=money+100 where name='zhangsan'";
			//预处理块
			state=conn.prepareStatement(sql2);
			//执行sql,获取结果
			int row2=state.executeUpdate();
			System.out.println(row2);
			//处理结果
			if(row>0 && row2>0){
				System.out.println("转账成功");
				conn.commit();//提交
			}else{
				System.out.println("转账失败");
				conn.rollback();//回滚
			}	
			
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally{
			DBUtils.close(null, state, conn);
		}
		
	}

BaseDao

作用：

• basedao实现数据库的增删改
• basedao实现数据库的查询
  示例：
  javabeen

public class User {
	private int id;
	private String uname;
	private int upwd;
	
	public User() {
		super();
	}

	public User(int id, String uname, int upwd) {
		super();
		this.id = id;
		this.uname = uname;
		this.upwd = upwd;
	}

	@Override
	public String toString() {
		return "User [id=" + id + ", uname=" + uname + ", upwd=" + upwd + "]";
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getUname() {
		return uname;
	}

	public void setUname(String uname) {
		this.uname = uname;
	}

	public int getUpwd() {
		return upwd;
	}

	public void setUpwd(int upwd) {
		this.upwd = upwd;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		result = prime * result + ((uname == null) ? 0 : uname.hashCode());
		result = prime * result + upwd;
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		User other = (User) obj;
		if (id != other.id)
			return false;
		if (uname == null) {
			if (other.uname != null)
				return false;
		} else if (!uname.equals(other.uname))
			return false;
		if (upwd != other.upwd)
			return false;
		return true;
	}
	
	
}

DaseDao.java

import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

/**
 * 数据库通过访问对象
 * 	1.增删改的功能
 * 	2.查询的功能
 * @author zhuch
 *
 */
public class BaseDao<T> {
	//查询	返回值List	参数：sql	值
	public List<T> testQuery(String sql,Class<T> cls,Object ... args){
		List<T> ls=new ArrayList();
		boolean flag=false;
		Connection conn=null;
		PreparedStatement state=null;
		ResultSet result=null;
		ResultSetMetaData meta=null;
		try {
			conn=DBUtils.getConnection();
			state = conn.prepareStatement(sql);
			//为?赋值
			if(args!=null && args.length!=0){
				for(int i=0;i<=args.length-1;i++){
					state.setObject(i+1,args[i]);
				}
			}
			//结果集
			result=state.executeQuery();
			
			//结果集的原信息对象
			meta = result.getMetaData();
			int columnNum = meta.getColumnCount();
			
			while(result.next()){
				//进了就有一个对象
				T t = cls.newInstance();//默认调用空构造
				for(int i=1;i<=columnNum;i++){
					//2.从结果集中获取每一个字段的值
					Object value = result.getObject(i);
					//1.创建一个对应类型的成员属性 getDeclaredField(String name)
					String name = meta.getColumnLabel(i);
					//3.获取对应java类中的对应属性
					Field field = cls.getDeclaredField(name);
					field.setAccessible(true);//设置值
					//4.给这个属性赋值
					field.set(t, value);
					field.setAccessible(false);
				}
				//5.把对象放入list容器
				ls.add(t);
			}
			
			//System.out.println(meta.getColumnCount());
			//System.out.println(meta.getColumnLabel(1));
			
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (InstantiationException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (IllegalAccessException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (NoSuchFieldException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (SecurityException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}finally{
				DBUtils.close(result, state, conn);
			}
		
			return ls;
	}
	
	
	
	//增删改
	public boolean testUpdate(String sql,Object ... args){
		boolean flag=false;
		Connection conn=null;
		PreparedStatement state=null;
		try {
			conn=DBUtils.getConnection();
			state = conn.prepareStatement(sql);
			//为?赋值
			for(int i=0;i<=args.length-1;i++){
				state.setObject(i+1,args[i]);
			}
		int row=state.executeUpdate();
		if(row>0){
			flag=true;
		}
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally{
			DBUtils.close(null, state, conn);
		}
		return flag;
	}
	
	/*
	 * 可变参数	相同的数据类型的0~多个参数
	 * 	1.数据类型...参数名,0~n个
	 * 	2.必须定义在参数列表的最后
	 * 	3.通过数组的操作方式去使用，会隐式的为可变参数定义一个数组
	 */
	
	/*public static void test(int a,String ...s){
		
	}*/
}

实用：Test.java

import java.util.List;

import com.shsxt.bean.User;
import com.shsxt.utils.BaseDao;

public class Test {
	public static void main(String[] args) {
		//BaseDao base=new BaseDao();
		//String sql="insert into sxt_user values(sq_num.nextval,?,?)";
		String sql="delete from sxt_user where uname=?";
		//boolean flag=base.testUpdate(sql, "zcp1","123");
		/*boolean flag=base.testUpdate(sql, "zcp1");
		if(flag){
			System.out.println("操作成功");
		}else{
			System.out.println("操作失败");
		}*/
		
		
		BaseDao<User> base=new BaseDao<User>();
		//String sql2="select id,uname,upwd from sxt_user";
		String sql2="select uname \"uname\" from sxt_user";
		List<User> ls = base.testQuery(sql2, User.class);
		System.out.println(ls);
	}
}