newssystem.zip

package com.newssys.ssm.basedao; import java.lang.reflect.Field; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.sql.*; import java.util.ArrayList; import java.util.List; public abstract class BaseDAO<T> { public final String DRIVER = "com.mysql.cj.jdbc.Driver" ; public final String URL = "jdbc:mysql://localhost:3306/demo?useUnicode=true&characterEncoding=utf-8"; public final String USER = "root"; public final String PWD = "root" ; protected Connection conn ; protected PreparedStatement psmt ; protected ResultSet rs ; //T的Class对象 private Class entityClass ; public BaseDAO(){ //getClass() 获取Class对象，当前我们执行的是new FruitDAOImpl() , 创建的是FruitDAOImpl的实例 //那么子类构造方法内部首先会调用父类（BaseDAO）的无参构造方法 //因此此处的getClass()会被执行，但是getClass获取的是FruitDAOImpl的Class //所以getGenericSuperclass()获取到的是BaseDAO的Class Type genericType = getClass().getGenericSuperclass(); //ParameterizedType 参数化类型 Type[] actualTypeArguments = ((ParameterizedType) genericType).getActualTypeArguments(); //获取到的<T>中的T的真实的类型 Type actualType = actualTypeArguments[0]; try { entityClass = Class.forName(actualType.getTypeName()); } catch (ClassNotFoundException e) { e.printStackTrace(); } } protected Connection getConn(){ try { //1.加载驱动 Class.forName(DRIVER); //2.通过驱动管理器获取连接对象 return DriverManager.getConnection(URL, USER, PWD); } catch (ClassNotFoundException | SQLException e) { e.printStackTrace(); } return null ; } protected void close(ResultSet rs , PreparedStatement psmt , Connection conn){ try { if (rs != null) { rs.close(); } if(psmt!=null){ psmt.close(); } if(conn!=null && !conn.isClosed()){ conn.close(); } } catch (SQLException e) { e.printStackTrace(); } } //给预处理命令对象设置参数 private void setParams(PreparedStatement psmt , Object... params) throws SQLException { if(params!=null && params.length>0){ for (int i = 0; i < params.length; i++) { psmt.setObject(i+1,params[i]); } } } //执行更新，返回影响行数 protected int executeUpdate(String sql , Object... params){ boolean insertFlag = false ; insertFlag = sql.trim().toUpperCase().startsWith("INSERT"); try { conn = getConn(); if(insertFlag){ psmt = conn.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS); }else { psmt = conn.prepareStatement(sql); } setParams(psmt,params); int count = psmt.executeUpdate() ; if(insertFlag){ rs = psmt.getGeneratedKeys(); if(rs.next()){ return ((Long)rs.getLong(1)).intValue(); } } return count ; } catch (SQLException e) { e.printStackTrace(); }finally { close(rs,psmt,conn); } return 0; } //通过反射技术给obj对象的property属性赋propertyValue值 private void setValue(Object obj, String property, Object propertyValue){ Class clazz = obj.getClass(); try { //获取property这个字符串对应的属性名 ， 比如 "fid" 去找 obj对象中的 fid 属性 Field field = clazz.getDeclaredField(property); if(field!=null){ field.setAccessible(true); field.set(obj, propertyValue); } } catch (NoSuchFieldException | IllegalAccessException e) { e.printStackTrace(); } } //执行复杂查询，返回例如统计结果 protected Object[] executeComplexQuery(String sql , Object... params){ try { conn = getConn() ; psmt = conn.prepareStatement(sql); setParams(psmt,params); rs = psmt.executeQuery(); //通过rs可以获取结果集的元数据 //元数据：描述结果集数据的数据 , 简单讲，就是这个结果集有哪些列，什么类型等等 ResultSetMetaData rsmd = rs.getMetaData(); //获取结果集的列数 int columnCount = rsmd.getColumnCount(); Object[] columnValueArr = new Object[columnCount]; //6.解析rs if(rs.next()){ for(int i = 0 ; i<columnCount;i++){ Object columnValue = rs.getObject(i+1); columnValueArr[i]=columnValue; } return columnValueArr ; } } catch (SQLException e) { e.printStackTrace(); } finally { close(rs,psmt,conn); } return null ; } //执行查询，返回单个实体对象 protected T load(String sql , Object... params){ try { conn = getConn() ; psmt = conn.prepareStatement(sql); setParams(psmt,params); rs = psmt.executeQuery(); //通过rs可以获取结果集的元数据 //元数据：描述结果集数据的数据 , 简单讲，就是这个结果集有哪些列，什么类型等等 ResultSetMetaData rsmd = rs.getMetaData(); //获取结果集的列数 int columnCount = rsmd.getColumnCount(); //6.解析rs if(rs.next()){ T entity = (T)entityClass.newInstance(); for(int i = 0 ; i<columnCount;i++){ String columnName = rsmd.getColumnName(i+1); Object columnValue = rs.getObject(i+1); setValue(entity,columnName,columnValue); } return entity ; } } catch (SQLException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InstantiationException e) { e.printStackTrace(); } finally { close(rs,psmt,conn); } return null ; } //执行查询，返回List protected List<T> executeQuery(String sql , Object... params){ List<T> list = new ArrayList<>(); try { conn = getConn() ; psmt = conn.prepareStatement(sql); setParams(psmt,params); rs = psmt.executeQuery(); //通过rs可以获取结果集的元数据 //元数据：描述结果集数据的数据 , 简单讲，就是这个结果集有哪些列，什么类型等等 ResultSetMetaData rsmd = rs.getMetaData(); //获取结果集的列数 int columnCount = rsmd.getColumnCount(); //6.解析rs while(rs.next()){ T entity = (T)entityClass.newInstance(); for(int i = 0 ; i<columnCount;i++){ String columnName = rsmd.getColumnName(i+1); Object columnValue = rs.getObject(i+1); setValue(entity,columnName,columnValue); } list.add(entity); } } catch (SQLException e) { e.printStackTrace(); } catch (IllegalA