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(); }}