详解JDBC数据库链接及相关方法的封装

public class Consql {
 private static Consql consql=null;//单例设计模式
 private Connection conn=null;//数据库链接
 private final String url;//数据库url
 private final String username;//数据库用户名
 private final String password;//数据库密码
 //驱动类的加载
 static{//以静态代码块的形式加载驱动类，静态代码块只在类加载的时候执行一次
  try {
   Class.forName("com.mysql.jdbc.Driver");
  } catch (ClassNotFoundException e) {
   e.printStackTrace();
  }
 }
 //构造函数
 private Consql(String url,String username,String password) throws SQLException{
  this.url = url;
  this.username = username;
  this.password = password;
  open();//创建连接
 }
 private Connection open() throws SQLException
 {
  try {//驱动器获取数据库链接
   conn=DriverManager.getConnection(url, username, password);
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   //e.printStackTrace();
   throw e;
  }  
  return conn;  
 }
 /**
  * 带限制条件查找
  * @param sql 带占位符？的sql语句
  * @param t 返回相关类型对象的类（T.class）
  * @param params 替换占位符的数据，为动态数组
  * @return ArrayList<T>
  * @throws SQLException 
  */
 public <T> ArrayList<T> select(String sql,Class<T> t,Object...params) throws SQLException
 {//获取T类所有public方法
  Method[] declaredMethods = t.getDeclaredMethods();
  //创建一个盛放该类型对象集合
  ArrayList<T> arrayList=new ArrayList<>();
  try (PreparedStatement pStatement=conn.prepareStatement(sql);)
  {   
   for(int i=0;i<params.length;i++)
   {
    pStatement.setObject(i+1, params[i]);
   }   
   try(ResultSet rSet=pStatement.executeQuery();) 
   {
    ResultSetMetaData rData=rSet.getMetaData();
    //获取查询到结果表的列数
    int columnCount = rData.getColumnCount();    
    while (rSet.next()) {
     T a=t.newInstance();//创建泛型类实例
     for(int i=0;i<columnCount;i++)
     {//获得方数组里的set方法，这里造成了局限性，只能数据库表列名与对象名一致，且只能是set方法
      String aString="set"+rData.getColumnName(i+1);
      for (Method method : declaredMethods) {
       if(method.getParameterCount()==1&&method.getReturnType().toString().equals("void")&&method.getName().equalsIgnoreCase(aString))
       {//这里存在问题，前两个判断条件基本没用，主要是最初不想用上面拼串的方式来判断是不是调用该参数的方法
        method.setAccessible(true);
        //利用反射调用该方法
        method.invoke(a, rSet.getObject(i+1));
        break;
       }
      }
     }
     arrayList.add(a);
    }
   } catch (InstantiationException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (IllegalAccessException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (IllegalArgumentException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (InvocationTargetException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } 
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   throw e;
  }
  return arrayList;  
 }
 /**
  * 数据插入
  * @param sql 带占位符？的sql语句
  * @param params 替换占位符的数据，动态数组
  * @throws SQLException
  */
 public void insert(String sql,Object...params) throws SQLException
 {
  try(PreparedStatement pStatement=conn.prepareStatement(sql);) {
   
   for(int i=0;i<params.length;i++)
   {
    pStatement.setObject(i+1, params[i]);
   }
   pStatement.executeUpdate();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   throw e;
  }
 }
 /**
  * 数据更新
  * @param sql 带占位符？的sql语句
  * @param params 替换占位符的数据，动态数组
  * @throws SQLException
  */
 public void update(String sql,Object...params) throws SQLException
 {
  try(PreparedStatement pStatement=conn.prepareStatement(sql);) {
   
   for(int i=0;i<params.length;i++)
   {
    pStatement.setObject(i+1, params[i]);
   }
   pStatement.executeUpdate();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   throw e;
  }
 }
 /**
  * 带限制条件删除
  * @param sql 带占位符？的sql语句
  * @param params 替换占位符的数据，动态数组
  * @throws SQLException
  */
 public void delete(String sql,Object...params) throws SQLException
 {
  try(PreparedStatement pStatement=conn.prepareStatement(sql);) {
   
   for(int i=0;i<params.length;i++)
   {
    pStatement.setObject(i+1, params[i]);
   }
   pStatement.executeUpdate();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   throw e;
  }
 }
 /**
  * 删除全部，不带有限制
  * @param sql
  * @throws SQLException
  */
 public void deleteall(String sql) throws SQLException
 {
  try(PreparedStatement pStatement=conn.prepareStatement(sql);) {      
   pStatement.executeUpdate();
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   throw e;
  }
 }
 /**
  * 无限制条件查找
  * @param sql 
  * @param t 泛型类T.class
  * @return ArrayList<T>
  * @throws SQLException 
  */
 public <T> ArrayList<T> select(String sql,Class<T> t) throws SQLException
 {
  Method[] declaredMethods = t.getDeclaredMethods();
  ArrayList<T> arrayList=new ArrayList<>();
  try (PreparedStatement pStatement=conn.prepareStatement(sql);)
  {      
   try(ResultSet rSet=pStatement.executeQuery();) 
   {
    ResultSetMetaData rData=rSet.getMetaData();
    int columnCount = rData.getColumnCount();    
    while (rSet.next()) {
     T a=t.newInstance();
     for(int i=0;i<columnCount;i++)
     {
      String aString="set"+rData.getColumnName(i+1);
      for (Method method : declaredMethods) {
       if(method.getName().equalsIgnoreCase(aString))
       {
        method.setAccessible(true);
        method.invoke(a, rSet.getObject(i+1));
        break;
       }
      }
     }
     arrayList.add(a);
    }
   } catch (InstantiationException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (IllegalAccessException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (IllegalArgumentException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (InvocationTargetException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } 
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   throw e;
  }
  return arrayList; 
 }
 /**
  * 返回表中数据行数
  * @param tableName 数据库表名
  * @return 行数
  * @throws SQLException
  */
 public int count(String tableName) throws SQLException
 {
  String sql="select count(*) from "+tableName;
  try(PreparedStatement pStatement=conn.prepareStatement(sql);
    ResultSet rsSet=pStatement.executeQuery(); )
  {  
   if(rsSet.next())
   {
    return rsSet.getInt(1);
   }   
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   throw e;
  }
  return 0;
 }
 /**
  * 判断数据是否存在
  * @param sql 带占位符？的sql语句
  * @param params 替换占位符的数据，动态数组
  * @return boolean
  * @throws SQLException
  */
 public boolean isExist(String sql,Object...params) throws SQLException
 {  
  try(PreparedStatement pStatement=conn.prepareStatement(sql);)
  {
   for(int i=0;i<params.length;i++)
   {
    pStatement.setObject(i+1, params[i]);
   }
   try(ResultSet rsSet=pStatement.executeQuery();) {
    if(rsSet.next())
    {
     return true;
    }
   } finally {
    
   }
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   throw e;
  }
  return false;  
 }
 /**
  * 创建实例
  * @param url 数据库url
  * @param username 用户名
  * @param password 密码
  * @return consql对象
  * @throws SQLException
  */
 public static Consql getnewInstance(String url,String username,String password) throws SQLException
 {
  if(consql==null)
   consql=new Consql(url, username, password);
  return consql;  
 }
 //垃圾回收，貌似并不能达到析构函数的效果
 protected void finalize() throws Throwable
 {
  if(conn!=null)
  {
   conn.close();  
  }
  super.finalize();
 }
}