后端开发DAO及其相关类，DAO的优化

Posted 2023-02-21 cls1277

优化前

BaseDAO.java

package com.cls1277.dao;

import com.cls1277.utils.JDBCutils;
import org.junit.Test;

import java.lang.reflect.Field;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

//抽象类
public abstract class BaseDAO 
    public void update(Connection conn, String sql, Object ... args) 
        PreparedStatement ps = null;
        try 
            ps = conn.prepareStatement(sql);
            for(int i=0; i<args.length; i++) 
                ps.setObject(i+1, args[i]);
            
            ps.execute();
         catch (Exception e) 
            e.printStackTrace();
         finally 
            JDBCutils.closeResource(null, ps);
        
    

    public <T> T getInstance1(Connection conn, Class<T> clazz, String sql, Object ... args) 
        PreparedStatement ps = null;
        ResultSet rs = null;
        try 
            ps = conn.prepareStatement(sql);
            for(int i=0; i<args.length; i++) 
                ps.setObject(i+1, args[i]);
            
            rs = ps.executeQuery();
            ResultSetMetaData rsmd = rs.getMetaData();
            int columnCount = rsmd.getColumnCount();
            if(rs.next()) 
                T t = clazz.newInstance();
                for(int i=0; i<columnCount; i++) 
                    Object columnValue = rs.getObject(i+1);
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t, columnValue);
                
                return t;
            
         catch (Exception e) 
            e.printStackTrace();
         finally 
            JDBCutils.closeResource(null, ps, rs);
        
        return null;
    

    public <T> List<T> getInstance2(Connection conn, Class<T> clazz, String sql, Object ... args) 
        PreparedStatement ps = null;
        ResultSet rs = null;
        try 
            ps = conn.prepareStatement(sql);
            for(int i=0; i<args.length; i++) 
                ps.setObject(i+1, args[i]);
            
            rs = ps.executeQuery();
            ResultSetMetaData rsmd = rs.getMetaData();
            int columnCount = rsmd.getColumnCount();
            ArrayList<T> ts = new ArrayList<>();
            while(rs.next()) 
                T t = clazz.newInstance();
                for(int i=0; i<columnCount; i++) 
                    Object columnValue = rs.getObject(i+1);
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t, columnValue);
                
                ts.add(t);
            
            return ts;
         catch (Exception e) 
            e.printStackTrace();
         finally 
            JDBCutils.closeResource(null, ps, rs);
        
        return null;
    

    //泛型
    public <E> E getValue(Connection conn, String sql, Object ... args) 
        PreparedStatement ps = null;
        ResultSet rs = null;
        try 
            ps = conn.prepareStatement(sql);
            for(int i=0; i<args.length; i++) 
                ps.setObject(i+1, args[i]);
            
            rs = ps.executeQuery();
            if(rs.next()) 
                return (E) rs.getObject(1);
            
         catch (Exception e) 
            e.printStackTrace();
         finally 
            JDBCutils.closeResource(null, ps, rs);
        
        return null;
    

//    @Test
//    public void getValueTest() throws SQLException, IOException, ClassNotFoundException 
//        Connection conn = JDBCutils.getConnection();
//        String sql = "select count(*) from user_table";
//        long ans = getValue(conn, sql);
//        System.out.println(ans);
//    

CustomerDAO.java(接口)

package com.cls1277.dao;

import com.cls1277.preparedstatement.customer.Customer;

import java.sql.Connection;
import java.sql.Date;
import java.util.List;

//接口：规范针对于customers表的操作
public interface CustomerDAO 
    //加文档注释最好
    void insert(Connection conn, Customer customer);
    void delete(Connection conn, int id);
    void update(Connection conn, Customer customer);
    Customer getCustomer(Connection conn, int id);
    List<Customer> getAll(Connection conn);
    Long getCount(Connection conn);
    Date getMaxDate(Connection conn);

CustomerDAOImpl(CustomerDAO的实现)

package com.cls1277.dao;

import com.cls1277.preparedstatement.customer.Customer;

import java.sql.Connection;
import java.sql.Date;
import java.util.List;

public class CustomerDAOImpl extends BaseDAO implements CustomerDAO

    @Override
    public void insert(Connection conn, Customer customer) 
        String sql = "insert into customers(name, email, birth)value(?,?,?)";
        update(conn, sql, customer.getName(), customer.getEmail(), customer.getBirth());
    

    @Override
    public void delete(Connection conn, int id) 
        String sql = "delete from customers where id = ?";
        update(conn, sql, id);
    

    @Override
    public void update(Connection conn, Customer customer) 
        String sql = "update customers set name = ?, email = ?, birth = ? where id = ?";
        update(conn, sql, customer.getName(), customer.getEmail(), customer.getBirth(), customer.getId());
    

    @Override
    public Customer getCustomer(Connection conn, int id) 
        String sql = "select id,name,email,birth from customers where id = ?";
        return getInstance1(conn, Customer.class, sql, id);
    

    @Override
    public List<Customer> getAll(Connection conn) 
        String sql = "select id,name,email,birth from customers";
        return getInstance2(conn, Customer.class, sql);
    

    @Override
    public Long getCount(Connection conn) 
        String sql = "select count(*) from customers";
        return getValue(conn, sql);
    

    @Override
    public Date getMaxDate(Connection conn) 
        String sql = "select max(birth) from customers";
        return getValue(conn, sql);
    

优化后

优化的地方在于：因为我的这个DAO是针对customers表的，所以就没必要在代码中再获取一下Customer这个类，只需要在BaseDAO里使用反射的方法获取到当前子类的父类的泛型即可。

BaseDAO.java

package com.cls1277.daoplus;

import com.cls1277.utils.JDBCutils;

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

//抽象类
public abstract class BaseDAO<T> 
    private Class<T> clazz = null;

//    public BaseDAO() 
//
//    
    
        //获取当前子类继承的父类的泛型
        //如何理解？https://blog.csdn.net/qq_26424655/article/details/71515741
        Type genericSuperclass = this.getClass().getGenericSuperclass();
        ParameterizedType paramType = (ParameterizedType) genericSuperclass;
        Type[] actualTypeArguments = paramType.getActualTypeArguments();
        clazz = (Class<T>) actualTypeArguments[0];
    
    public void update(Connection conn, String sql, Object ... args) 
        PreparedStatement ps = null;
        try 
            ps = conn.prepareStatement(sql);
            for(int i=0; i<args.length; i++) 
                ps.setObject(i+1, args[i]);
            
            ps.execute();
         catch (Exception e) 
            e.printStackTrace();
         finally 
            JDBCutils.closeResource(null, ps);
        
    

    public T getInstance1(Connection conn, String sql, Object ... args) 
        PreparedStatement ps = null;
        ResultSet rs = null;
        try 
            ps = conn.prepareStatement(sql);
            for(int i=0; i<args.length; i++) 
                ps.setObject(i+1, args[i]);
            
            rs = ps.executeQuery();
            ResultSetMetaData rsmd = rs.getMetaData();
            int columnCount = rsmd.getColumnCount();
            if(rs.next()) 
                T t = clazz.newInstance();
                for(int i=0; i<columnCount; i++) 
                    Object columnValue = rs.getObject(i+1);
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t, columnValue);
                
                return t;
            
         catch (Exception e) 
            e.printStackTrace();
         finally 
            JDBCutils.closeResource(null, ps, rs);
        
        return null;
    

    public List<T> getInstance2(Connection conn, String sql, Object ... args) 
        PreparedStatement ps = null;
        ResultSet rs = null;
        try 
            ps = conn.prepareStatement(sql);
            for(int i=0; i<args.length; i++) 
                ps.setObject(i+1, args[i]);
            
            rs = ps.executeQuery();
            ResultSetMetaData rsmd = rs.getMetaData();
            int columnCount = rsmd.getColumnCount();
            ArrayList<T> ts = new ArrayList<>();
            while(rs.next()) 
                T t = clazz.newInstance();
                for(int i=0; i<columnCount; i++) 后端开发DAO及其相关类，DAO的优化

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