编写自己的JDBC框架

目的

简化代码，提高开发效率

设计模式

策略设计模式

代码

 #连接设置
 driverClassName=com.mysql.jdbc.Driver
 url=jdbc:mysql://localhost:3306/day17
 username=root
 password=sorry

 #<!-- 初始化连接 -->
 initialSize=10

 #最大连接数量
 maxActive=50

 #<!-- 最大空闲连接 -->
 maxIdle=20

 #<!-- 最小空闲连接 -->
 minIdle=5

 #<!-- 超时等待时间以毫秒为单位 6000毫秒/1000等于60秒 -->
 maxWait=60000

 #JDBC驱动建立连接时附带的连接属性属性的格式必须为这样：[属性名=property;]
 #注意："user" 与 "password" 两个属性会被明确地传递，因此这里不需要包含他们。
 connectionProperties=useUnicode=true;characterEncoding=utf8

 #指定由连接池所创建的连接的自动提交（auto-commit）状态。
 defaultAutoCommit=true

 #driver default 指定由连接池所创建的连接的只读（read-only）状态。
 #如果没有设置该值，则“setReadOnly”方法将不被调用。（某些驱动并不支持只读模式，如：Informix）
 defaultReadOnly=

 #driver default 指定由连接池所创建的连接的事务级别（TransactionIsolation）。
 #可用值为下列之一：（详情可见javadoc。）NONE,READ_UNCOMMITTED, READ_COMMITTED, REPEATABLE_READ, SERIALIZABLE
 defaultTransactionIsolation=REPEATABLE_READ

dbcpconfig.properties

 import java.util.List;
 import org.junit.Test;
 import com.itheima.dbassist.BeanHandler;
 import com.itheima.dbassist.BeanListHandler;
 import com.itheima.dbassist.DBAssist;
 import com.itheima.domain.User;
 import com.itheima.util.DBCPUtil;

 public class UserDaoImpl {
     private DBAssist da = new DBAssist(DBCPUtil.getDataSource());
     //SQL和参数
     @Test
     public void add(){
         da.update("insert into user values(?,?,?,?)", "aa","wf","123","非同寻常");
     }
     @Test
     public void update(){
         da.update("update user set password=? where id=?", "12345","aa");
     }
     @Test
     public void delete(){
         da.update("delete from user where id=?", "aa");
     }
     @Test
     public void query1(){
         User user = (User)da.query("select * from user where id=?", new BeanHandler(User.class), "a5cc6e18-f3b8-44a6-bcdd-c6476f1edb87");
         System.out.println(user);
     }
     @Test
     public void query2(){
         List<User> users = (List<User>)da.query("select * from user", new BeanListHandler(User.class));
         for(User user:users)
             System.out.println(user);
     }
 }

UserDaoImpl

 import java.lang.reflect.Field;
 import java.sql.ResultSet;
 import java.sql.ResultSetMetaData;
 import java.util.ArrayList;
 import java.util.List;
 /**
  * 适合有多条结果记录的数据封装
  * 返回的是一个List
  *
  */
 public class BeanListHandler implements ResultSetHandler {
     private Class clazz;
     public BeanListHandler(Class clazz){
         this.clazz = clazz;
     }
     public Object handle(ResultSet rs) {
         try {
             List list = new ArrayList();
             while(rs.next()){
                 Object bean = clazz.newInstance();
                 //封装数据：书写JavaBean的前提，类中的字段名或属性名与数据库表的字段名保持一致
                 ResultSetMetaData rsmd = rs.getMetaData();
                 int columnCount = rsmd.getColumnCount();
                 for(int i=0;i<columnCount;i++){
                     String columnName = rsmd.getColumnName(i+1);//与JavaBean的字段名一致
                     Object columnValue = rs.getObject(columnName);//列值

                     //得到JavaBean的对应字段
                     Field field = clazz.getDeclaredField(columnName);
                     field.setAccessible(true);//强暴它 有可能是私有的
                     field.set(bean, columnValue);
                 }
                 list.add(bean);

             }
             return list;
         } catch (Exception e) {
             throw new RuntimeException("封装数据失败");
         }
     }
 }

BeanListHandler

 import java.sql.Connection;
 import java.sql.ParameterMetaData;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;

 import javax.sql.DataSource;

 import com.itheima.util.DBCPUtil;

 public class DBAssist {
     private DataSource dataSource;
     public DBAssist(DataSource dataSource){
         this.dataSource = dataSource;
     }
     /*
      * 能够执行DML语句：INSERT UPDATE DELETE
      */
     public void update(String sql,Object...params){
         Connection conn = null;
         PreparedStatement stmt = null;
         ResultSet rs = null;
         try{
             conn = dataSource.getConnection();//具体的数据源无关
             stmt = conn.prepareStatement(sql);
             //看sql中的占位符的个数：参数元信息的获取
             ParameterMetaData pmd = stmt.getParameterMetaData();
             int paramCount = pmd.getParameterCount();
             //设置参数：略
             if(paramCount>0){
                 //判断参数占位符的个数和params的个数是否一致
                 if(params==null||params.length!=paramCount){
                     throw new RuntimeException("参数个数不匹配");
                 }
                 //设置SQL中的参数占位符的值
                 for(int i=0;i<paramCount;i++){
                     stmt.setObject(i+1, params[i]);
                 }
             }
             stmt.executeUpdate();
         }catch(Exception e){
             throw new RuntimeException(e);
         }finally{
             release(rs, stmt, conn);
         }
     }
     /**
      * 执行查询
      * @return 封装了数据的对象
      */
     public Object query(String sql,ResultSetHandler handler,Object...params){
         Connection conn = null;
         PreparedStatement stmt = null;
         ResultSet rs = null;
         try{
             conn = dataSource.getConnection();
             stmt = conn.prepareStatement(sql);
             //看sql中的占位符的个数：参数元信息的获取
             ParameterMetaData pmd = stmt.getParameterMetaData();
             int paramCount = pmd.getParameterCount();
             //设置参数：略
             if(paramCount>0){
                 //判断参数占位符的个数和params的个数是否一致
                 if(params==null||params.length!=paramCount){
                     throw new RuntimeException("参数个数不匹配");
                 }
                 //设置SQL中的参数占位符的值
                 for(int i=0;i<paramCount;i++){
                     stmt.setObject(i+1, params[i]);
                 }
             }
             rs = stmt.executeQuery();//如何封装呢：
                                         //有结果集：不知道有什么字段和值
                                         //不知道封装成什么对象：谁用谁知道

                                     //策略：有数据----->有目标
             return handler.handle(rs);
         }catch(Exception e){
             throw new RuntimeException(e);
         }finally{
             release(rs, stmt, conn);
         }
     }
     private void release(ResultSet rs,Statement stmt,Connection conn){
         if(rs!=null){
             try {
                 rs.close();
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             rs = null;
         }
         if(stmt!=null){
             try {
                 stmt.close();
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             stmt = null;
         }
         if(conn!=null){
             try {
                 conn.close();
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             conn = null;
         }
     }
 }    

DBAssist

 package com.itheima.dbassist;

 import java.sql.ResultSet;
 //抽象策略
 public interface ResultSetHandler {
     /**
      *把结果集中的数据封装到对象中
      * @param rs
      * @return
      */
     Object handle(ResultSet rs);
 }

ResultSetHandler

 import java.lang.reflect.Field;
 import java.sql.ResultSet;
 import java.sql.ResultSetMetaData;
 //策略的具体实现
 /**
  * 专门用于封装结果中只有一条的记录的情况
  * 返回值：封装好的Java对象
  *
  */
 public class BeanHandler implements ResultSetHandler {
     private Class clazz;
     public BeanHandler(Class clazz){
         this.clazz = clazz;
     }
     public Object handle(ResultSet rs) {
         try {
             if(rs.next()){
                 Object bean = clazz.newInstance();
                 //封装数据：书写JavaBean的前提，类中的字段名或属性名与数据库表的字段名保持一致
                 ResultSetMetaData rsmd = rs.getMetaData();
                 int columnCount = rsmd.getColumnCount();
                 for(int i=0;i<columnCount;i++){
                     String columnName = rsmd.getColumnName(i+1);//与JavaBean的字段名一致
                     Object columnValue = rs.getObject(columnName);//列值

                     //得到JavaBean的对应字段
                     Field field = clazz.getDeclaredField(columnName);
                     field.setAccessible(true);//强暴它 有可能是私有的
                     field.set(bean, columnValue);
                 }

                 return bean;
             }
             return null;
         } catch (Exception e) {
             throw new RuntimeException("封装数据失败");
         }
     }

 }

BeanHandler

 public class User {
     private String id;
     private String username;
     private String password;
     private String nick;
     public String getId() {
         return id;
     }
     public void setId(String id) {
         this.id = id;
     }
     public String getUsername() {
         return username;
     }
     public void setUsername(String username) {
         this.username = username;
     }
     public String getPassword() {
         return password;
     }
     public void setPassword(String password) {
         this.password = password;
     }
     public String getNick() {
         return nick;
     }
     public void setNick(String nick) {
         this.nick = nick;
     }
     @Override
     public String toString() {
         return "User [id=" + id + ", username=" + username + ", password="
                 + password + ", nick=" + nick + "]";
     }

 }

User

 import java.io.InputStream;
 import java.sql.Connection;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.Properties;

 import javax.sql.DataSource;

 import org.apache.commons.dbcp.BasicDataSourceFactory;

 public class DBCPUtil {
     private static DataSource dataSource;
     static{
         try {
             InputStream in = DBCPUtil.class.getClassLoader().getResourceAsStream("dbcpconfig.properties");
             Properties props = new Properties();
             props.load(in);
             dataSource = BasicDataSourceFactory.createDataSource(props);
         } catch (Exception e) {
             throw new ExceptionInInitializerError("初始化数据源失败");
         }
     }
     public static Connection getConnection(){
         try {
             return dataSource.getConnection();
         } catch (SQLException e) {
             throw new RuntimeException("获取数据库连接失败");
         }
     }
     public static DataSource getDataSource(){
         return dataSource;
     }

 }

DBCPUtil