jdbc都有什么设计模式我是一个新手,昨天

发布网友发布时间：2022-04-10 11:47

共2个回答

懂视网时间：2022-04-10 16:08

com.itheima.domain; //一般：实体类的字段名和数据库表的字段名保持一致 //约定优于编码 public class Account { private int id; private String name; private float money; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public float getMoney() { return money; } public void setMoney(float money) { this.money = money; } @Override public String toString() { return "Account [id=" + id + ", name=" + name + ", money=" + money + "]"; } }

package com.itheima.util;

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.SQLException;
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(e);
 }
 }
 
 public static DataSource getDataSource(){
 return dataSource;
 }
 
 public static Connection getConnection(){
 try {
  return dataSource.getConnection();
 } catch (SQLException e) {
  throw new RuntimeException(e);
 }
 }
}

package com.itheima.dbassist;

import java.sql.ResultSet;

public interface ResultSetHandler {
 /**
 * 把结果中的数据封装到指定的对象中
 * @param rs
 * @return 封装了数据的对象
 */
 Object handle(ResultSet rs);
}

package com.itheima.dbassist;

import java.lang.reflect.Field;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
/**
 * 封装到JavaBean中
 * 满足约定：数据库字段名和JavaBean字段名保持一致
 * @author wzhting
 *
 */
public class BeanListHanlder implements ResultSetHandler {
 
 private Class clazz;//目标类型
 public BeanListHanlder(Class clazz){
 this.clazz = clazz;
 }

 public Object handle(ResultSet rs) {
 try {
  List list = new ArrayList();
  while(rs.next()){
  //有记录
  Object bean = clazz.newInstance();//目标对象
  //有多少列，列名和值又是什么？
  ResultSetMetaData rsmd = rs.getMetaData();
  int count = rsmd.getColumnCount();//列数
  for(int i=0;i<count;i++){
   String fieldName = rsmd.getColumnName(i+1);//得到数据库字段名，也就得到了JavaBan的字段名
   Object fieldValue = rs.getObject(fieldName);//字段值
   //通过字段反射
   Field f = clazz.getDeclaredField(fieldName);
   f.setAccessible(true);
   f.set(bean, fieldValue);
  }
  list.add(bean);
  }
  return list;
 } catch (Exception e) {
  throw new RuntimeException(e);
 }
 }

}

package com.itheima.dbassist;

import java.lang.reflect.Field;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
/**
 * 适合只有一条查询结果的情况
 * 封装到JavaBean中
 * 满足约定：数据库字段名和JavaBean字段名保持一致
 * @author wzhting
 *
 */
public class BeanHanlder implements ResultSetHandler {
 
 private Class clazz;//目标类型
 public BeanHanlder(Class clazz){
 this.clazz = clazz;
 }

 public Object handle(ResultSet rs) {
 try {
  if(rs.next()){
  //有记录
  Object bean = clazz.newInstance();//目标对象
  //有多少列，列名和值又是什么？
  ResultSetMetaData rsmd = rs.getMetaData();
  int count = rsmd.getColumnCount();//列数
  for(int i=0;i<count;i++){
   String fieldName = rsmd.getColumnName(i+1);//得到数据库字段名，也就得到了JavaBan的字段名
   Object fieldValue = rs.getObject(fieldName);//字段值
   //通过字段反射
   Field f = clazz.getDeclaredField(fieldName);
   f.setAccessible(true);
   f.set(bean, fieldValue);
  }
  return bean;
  }
  return null;
 } catch (Exception e) {
  throw new RuntimeException(e);
 }
 }

}

package com.itheima.dbassist;

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;

/**
 * 框架的核心类
 * @author wzhting
 *
 */
public class DBAssist {
 private DataSource dataSource;
 public DBAssist(DataSource dataSource){
 this.dataSource = dataSource;
 }
 //写：添加、删除、修改
 //params参数要和sql中的占位符对应
 public void update(String sql,Object...params) {
 Connection conn = null;
 PreparedStatement stmt = null;
 ResultSet rs = null;
 try{
  conn = dataSource.getConnection();
  stmt = conn.prepareStatement(sql);
  //设置参数
  //得到sql中的参数
  ParameterMetaData pmd = stmt.getParameterMetaData();
  int count = pmd.getParameterCount();
  if(count>0){
   if(params==null){
   throw new RuntimeException("必须传入参数的值");
   }
   if(count!=params.length){
   throw new RuntimeException("参数数量不匹配");
   }
   for(int i=0;i<count;i++){
   stmt.setObject(i+1, params[i]);
   }
   
  }
  
  stmt.executeUpdate();
 }catch(Exception e){
  throw new RuntimeException(e);
 }finally{
  release(rs, stmt, conn);
 }
 }
 
 
 //读：查询
 public Object query(String sql,ResultSetHandler rsh,Object...params) {
 Connection conn = null;
 PreparedStatement stmt = null;
 ResultSet rs = null;
 try{
  conn = dataSource.getConnection();
  stmt = conn.prepareStatement(sql);
  //设置参数
  //得到sql中的参数
  ParameterMetaData pmd = stmt.getParameterMetaData();
  int count = pmd.getParameterCount();
  if(count>0){
   if(params==null){
   throw new RuntimeException("必须传入参数的值");
   }
   if(count!=params.length){
   throw new RuntimeException("参数数量不匹配");
   }
   for(int i=0;i<count;i++){
   stmt.setObject(i+1, params[i]);
   }
   
  }
  
  rs = stmt.executeQuery();
  //有结果集，要封装到对象中。策略设计模式
  return rsh.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;
 }
 }
}

package com.itheima.test;

import java.util.List;

import org.junit.Test;

import com.itheima.dbassist.BeanHanlder;
import com.itheima.dbassist.BeanListHanlder;
import com.itheima.dbassist.DBAssist;
import com.itheima.domain.Account;
import com.itheima.util.DBCPUtil;

public class DBAssistTest {
 private DBAssist da = new DBAssist(DBCPUtil.getDataSource());
 @Test
 public void testAdd(){
 da.update("insert into account values (?,?,?)", 7,"ggg",1000);
 }
 @Test
 public void testUpdate(){
 da.update("update account set money=? where id=?", 10000,7);
 }
 @Test
 public void testDel(){
 da.update("delete from account where id=?",7);
 }
 @Test
 public void testQueryOne(){
 Object obj = da.query("select * from account where id=?",new BeanHanlder(Account.class),2);
 System.out.println(obj);
 }
 @Test
 public void testQueryAll(){
 List list = (List)da.query("select * from account",new BeanListHanlder(Account.class));
 for(Object o:list)
  System.out.println(o);
 }
}

编写JDBC框架：（策略设计模式）

标签：column resultset cut 设置 junit .com sys span 目标

热心网友时间：2022-04-10 13:16

应该不是线程安全的,DLL只是共享进程的堆栈而不是共享线程的堆栈.
只是上来让大家肯定一下.

这要看你的DLL里面的函数的处理了比如是否存在对同一资源的存取，是不是线程安全的。。
比如说你打开文件如果用独占方式打开那么是安全的否则可能会不安全。