• ORM框架，反射，泛型，注解，CRUD实现

    注解与反射：

    注：内容介绍_哔哩哔哩_bilibili

    注解就是对代码的注释，反射就是java理解注解的方式。反射可以在类运行时获取类相关属性，方法等。

    声明注解：@interface

    元注解：@Target @Retention @Document和@Inherited

    定义一个注解

    1. /**
    2.  * RetentionPolicy：
    3.  * SOURCE：在代码中，不会在class中
    4.  * CLASS: 编译在class，jvm会忽略
    5.  * RUNTTIME: 运行时生效
    6.  */
    7. @Target(ElementType.METHOD)   //可以表明注解用在类/方法/字段上
    8. @Retention(RetentionPolicy.RUNTIME)  //保留策略
    9. public @interface MyAnno {
    10.  
    11.     //默认的方法，会带到jvm中，会在反射中获得这些值
    12.     String value();
    13. }

    定义一个反射类

    1. @TableName(value = "类上注解")
    2. public class User {
    3.  
    4. //    @MyAnno(value = "通过反射获取默认值")
    5.     @TableField(value = "变量注解")
    6.     private String userId;
    7.  
    8.     @MyAnno(value = "通过反射获取方法注解")
    9.     private void work(String userId){
    10.         System.out.println("");
    11.     }
    12. }

     获取相关属性

    1. public class ReflecDemo {
    2.     public static void main(String[] args) {
    3.         TableName tableName = User.class.getAnnotation(TableName.class);  //通过反射获取对象
    4.         System.out.println(tableName.value());
    5.  
    6.         Field[] declaredFields = User.class.getDeclaredFields();  //获取对象变量
    7.         for (Field field : declaredFields) {
    8.             TableField tableField = field.getAnnotation(TableField.class);
    9.             if(null != tableField){
    10.                 System.out.println(field.getName() + "   -   " + tableField.value());
    11.             }
    12.         }
    13.  
    14.         Method[] declaredMethods = User.class.getDeclaredMethods();
    15.         for (Method method : declaredMethods) {
    16.             MyAnno myAnno = method.getAnnotation(MyAnno.class);
    17.             if(null != myAnno){
    18.                 System.out.println(method.getName() + " - " + myAnno.value());  //获取方法上注解
    19.             }
    20.         }
    21.     }
    22. }

    实现一个ORM框架

    目标：通过一个包含自定义注解的POJO类，来描述POJO与数据库中表的对应关系，然后由框架统一完成对数据库中表的CRUD操作。

    代码：许宇 (xuyu294636185) - Gitee.com

    步骤：

    1.定义实体与注解，从实体中解析出CRUD对应的SQL语句

    1. /**
    2.  * 定义table注解:指明orderInfo实体对应数据库的那张表
    3.  */
    4. @Target(ElementType.TYPE)
    5. @Retention(RetentionPolicy.RUNTIME)
    6. public @interface Table {
    7.     public String tableName();  //对应表名
    8.     public String orderBy() default "";  //排序字段，可为空
    9.     public String order() default "";  //升降序
    10. }
    1. /**
    2.  * 表中字段对应关系
    3.  */
    4. @Target(ElementType.FIELD)
    5. @Retention(RetentionPolicy.RUNTIME)
    6. public @interface TableColumn {
    7.     public String dbColumn();  //对应数据库列
    8.     public String isPK() default "";  //是否主键
    9.     public String dbColumnType() default "";  //数据库字段类型
    10. }
    1. @Table(tableName = "order_info",orderBy = "order_date",order = "desc")
    2. public class OrderInfo {
    3.  
    4.     @TableColumn(dbColumn = "order_id",isPK = "true")
    5.     private int orderId;
    6.     @TableColumn(dbColumn = "client_name")
    7.     private String clientName;
    8.     @TableColumn(dbColumn = "produce_name")
    9.     private String productName;
    10.     @TableColumn(dbColumn = "order_date")
    11.     private Date orderDate;
    12.  
    13.     public int getOrderId() {
    14.         return orderId;
    15.     }
    16.  
    17.     public void setOrderId(int orderId) {
    18.         this.orderId = orderId;
    19.     }
    20.  
    21.     public String getClientName() {
    22.         return clientName;
    23.     }
    24.  
    25.     public void setClientName(String clientName) {
    26.         this.clientName = clientName;
    27.     }
    28.  
    29.     public String getProductName() {
    30.         return productName;
    31.     }
    32.  
    33.     public void setProductName(String productName) {
    34.         this.productName = productName;
    35.     }
    36.  
    37.     public Date getOrderDate() {
    38.         return orderDate;
    39.     }
    40.  
    41.     public void setOrderDate(Date orderDate) {
    42.         this.orderDate = orderDate;
    43.     }
    44. }
    1. /**
    2.  * 对OrderInfo对象生成sql语句
    3.  */
    4. public class SQLProvider {
    5.  
    6.     //select xxx,xxx from table where xxx = 'xxx' and xxx = 'xxx' order by xxx desc|asc
    7.     public String genQuerySQL(OrderInfo orderInfo) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    8.         StringBuffer sql = new StringBuffer("select ");
    9.         StringBuffer paramSql = new StringBuffer();
    10.         StringBuffer whereSql = new StringBuffer(" where 1=1 ");
    11.  
    12.         Classextends OrderInfo> clazz = orderInfo.getClass();
    13.         Table table = clazz.getAnnotation(Table.class);
    14.         if (table == null) {
    15.             System.out.println("no table");
    16.         }
    17.         //拿到表名和排序字段和顺序
    18.         String tableName = table.tableName();
    19.         String order = table.order();
    20.         String orderBy = table.orderBy();
    21.  
    22.         Field[] fields = clazz.getDeclaredFields();
    23.         for (Field field : fields) {
    24.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    25.             if (tableColumn != null) {
    26.                 paramSql.append(tableColumn.dbColumn()).append(",");
    27.             }
    28.             String getterName = "get" + field.getName().substring(0, 1).toUpperCase() + field.getName().substring(1);
    29.             Object fieldValue = clazz.getMethod(getterName).invoke(orderInfo);//相当于orderInfo.getOrderId();
    30.             if(null==fieldValue || StringUtils.isEmpty(field.toString())){
    31.                 continue;
    32.             }
    33.             fieldValue = getColumnType(field, fieldValue);
    34.             whereSql.append(" and ").append(tableColumn.dbColumn()).append(" = ").append(fieldValue);
    35.         }
    36.  
    37.         sql.append(paramSql.substring(0, paramSql.length() - 1)).append(" from ").append(tableName).append(whereSql);
    38.         if (!StringUtils.isEmpty(orderBy)) {
    39.             sql.append(" order by ").append(orderBy);
    40.             if (!StringUtils.isEmpty(order)) {
    41.                 sql.append(" " + order);
    42.             }
    43.         }
    44.         return sql.toString();
    45.     }
    46.  
    47.     //update table set tableColumn = 'xxx',tableColumn = 'xxx' where pk = ?
    48.     public String genUpdateSQL(OrderInfo orderInfo) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    49.         StringBuffer sql = new StringBuffer("update ");
    50.         StringBuffer setSql = new StringBuffer(" set ");
    51.         StringBuffer whereSql = new StringBuffer();
    52.         StringBuffer columnSql = new StringBuffer();
    53.  
    54.         Classextends OrderInfo> clazz = orderInfo.getClass();
    55.         Table table = clazz.getAnnotation(Table.class);
    56.         if (null == table) {
    57.             System.out.println("未配置表名");
    58.         }
    59.         String tableName = table.tableName();
    60.  
    61.         //遍历tableColumn属性
    62.         for (Field field : clazz.getDeclaredFields()) {
    63.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    64.             if (tableColumn == null) {
    65.                 continue;
    66.             }
    67.             if (StringUtils.isEmpty(tableColumn.isPK())) {
    68.                 String getterName = "get" + field.getName().substring(0, 1).toUpperCase() + field.getName().substring(1);
    69.                 Object fieldValue = clazz.getMethod(getterName).invoke(orderInfo);//相当于orderInfo.getField();
    70.                 if (null == fieldValue) {
    71.                     continue;
    72.                 }
    73.                 fieldValue = getColumnType(field, fieldValue);
    74.                 columnSql.append(tableColumn.dbColumn()).append(" = ").append(fieldValue).append(" , ");
    75.             }
    76.         }
    77.         setSql.append(columnSql.substring(0, columnSql.length() - 2));
    78.         for (Field field : clazz.getDeclaredFields()) {
    79.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    80.             boolean ss = StringUtils.isEmpty(whereSql.toString());
    81.             if (!StringUtils.isEmpty(tableColumn.isPK()) && ss) {
    82.                 String getterName = "get" + field.getName().substring(0, 1).toUpperCase() + field.getName().substring(1);
    83.                 Object fieldValue = clazz.getMethod(getterName).invoke(orderInfo);//相当于orderInfo.getOrderId();
    84.                 if (null == fieldValue || StringUtils.isEmpty(field.toString())) {
    85.                     continue;
    86.                 }
    87.                 fieldValue = getColumnType(field, fieldValue);
    88.                 whereSql.append(" where ");
    89.                 whereSql.append(tableColumn.dbColumn()).append(" = ").append(fieldValue);
    90.             }
    91.             if (StringUtils.isEmpty(whereSql.toString())) {
    92.                 System.out.println("未设置主键，无法修改");
    93.             }
    94.         }
    95.         sql.append(tableName);
    96.         sql.append(setSql);
    97.         sql.append(whereSql);
    98.         return sql.toString();
    99.     }
    100.  
    101.     //delete from table where pk = ?
    102.     public String genDeleteSQL(OrderInfo orderInfo) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    103.         StringBuffer sql = new StringBuffer("delete from ");
    104.         StringBuffer where = new StringBuffer();
    105.  
    106.         //找到表名
    107.         Classextends OrderInfo> clazz = orderInfo.getClass();  //获取类对象
    108.         Table tableAnno = clazz.getAnnotation(Table.class);  //反射获取类属性
    109.         String tableName = tableAnno.tableName();  //拿到表名
    110.         if (null == tableAnno) {
    111.             System.out.println("未配置table注解");
    112.         }
    113.  
    114.         //找到列名
    115.         Field[] fields = clazz.getDeclaredFields();
    116.         for (Field field : fields) {
    117.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    118.             if (null == tableColumn) {
    119.                 continue;
    120.             }
    121.             if (!StringUtils.isEmpty(tableColumn.isPK()) && StringUtils.isEmpty(where.toString())) {
    122.                 //通过反射找到get方法获取orderid值
    123.                 String getterName = "get" + field.getName().substring(0, 1).toUpperCase() + field.getName().substring(1);
    124.                 Object fieldValue = clazz.getMethod(getterName).invoke(orderInfo);//相当于orderInfo.getOrderId();
    125.                 if (null == fieldValue) {
    126.                     System.out.println("未设置主键，无法删除");
    127.                     continue;
    128.                 }
    129.                 fieldValue = getColumnType(field, fieldValue);
    130.                 where.append(" WHERE ");
    131.                 where.append(tableColumn.dbColumn()).append(" = ").append(fieldValue);
    132.             }
    133.             //没有找到主键
    134.             if (StringUtils.isEmpty(where.toString())) {
    135.                 System.out.println("未设置主键，无法删除");
    136.             }
    137.         }
    138.  
    139.         //拼接sql
    140.         sql.append(tableName).append(where);
    141.         return sql.toString();
    142.     }
    143.  
    144.     public String genUpdateSQL2(OrderInfo orderInfo) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    145.         StringBuffer sql = new StringBuffer("update ");
    146.         StringBuffer setSql = new StringBuffer(" set ");
    147.         StringBuffer whereSql = new StringBuffer();
    148.  
    149.         Classextends OrderInfo> clazz = orderInfo.getClass();
    150.         Table table = clazz.getAnnotation(Table.class);
    151.         if (table == null) {
    152.             System.out.println("table null");
    153.         }
    154.         String tableName = table.tableName();
    155.  
    156.         Field[] fields = clazz.getDeclaredFields();
    157.         for (Field field : fields) {
    158.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    159.             if (tableColumn == null) {
    160.                 continue;
    161.             }
    162.             //通过反射找到get方法获取orderid值
    163.             String getterName = "get" + field.getName().substring(0, 1).toUpperCase() + field.getName().substring(1);
    164.             Object fieldValue = clazz.getMethod(getterName).invoke(orderInfo);//相当于orderInfo.getOrderId();
    165.             if (null != fieldValue && !StringUtils.isEmpty(fieldValue.toString()) && StringUtils.isEmpty(tableColumn.isPK())) {
    166.                 setSql.append(tableColumn.dbColumn()).append(" = ").append(fieldValue).append(",");
    167.             }
    168.  
    169.             if (!StringUtils.isEmpty(tableColumn.isPK()) && StringUtils.isEmpty(whereSql.toString())) {
    170.                 if (null == fieldValue) {
    171.                     System.out.println("pk is null");
    172.                 }
    173.                 fieldValue = getColumnType(field, fieldValue);
    174.                 whereSql.append(" WHERE ");
    175.                 whereSql.append(tableColumn.dbColumn()).append(" = ").append(fieldValue);
    176.             }
    177.         }
    178.         if (setSql.length() <= 5) {
    179.             System.out.println("no column update");
    180.         }
    181.         if (StringUtils.isEmpty(whereSql.toString())) {
    182.             System.out.println("pk is null");
    183.         }
    184.  
    185.         sql.append(tableName).append(setSql.substring(0, setSql.length() - 1)).append(whereSql);
    186.         return sql.toString();
    187.     }
    188.  
    189.     private Object getColumnType(Field field, Object fieldValue) {
    190.         //参数类型转换
    191.         if (field.getType() == String.class) {
    192.             fieldValue = "'" + fieldValue + "'";
    193.         } else if (field.getType() == int.class || field.getType() == Integer.class) {
    194.             //...各种类型转换
    195.         }
    196.         return fieldValue;
    197.     }
    198. }
    1. public class ReflectTest {
    2.     public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
    3.         //解析出orderInfo对应的CRUD操作的sql语句
    4.         OrderInfo orderInfo = new OrderInfo();
    5.         orderInfo.setOrderId(10001);
    6.         orderInfo.setClientName("客户1");
    7.         orderInfo.setProductName("商品1");
    8.  
    9.         SQLProvider sqlProvider = new SQLProvider();
    10.         System.out.println("增 :" + sqlProvider.genUpdateSQL2(orderInfo));
    11.         System.out.println("查 :" + sqlProvider.genQuerySQL(orderInfo));
    12.         System.out.println("删 :" + sqlProvider.genDeleteSQL(orderInfo));
    13.     }
    14. }

     遗留的问题：

    ①-传入参数是OederInfo，过于具体

    ②-异常没有处理

    ③-参数类型处理没有抽象出来

    2.封装成通用的Service

    1. /**
    2.  * 单例数据库链接
    3.  */
    4. public class DBUtil {
    5.  
    6.     private volatile static Connection connection;
    7.  
    8.     public static Connection getConnection(){
    9.         if(null == connection){
    10.             synchronized (DBUtil.class){
    11.                 if(null == connection){
    12.                     try {
    13.                         Class.forName("com.mysql.cj.jdbc.Driver");
    14.                         connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test?characterEncoding=utf8&serverTimezone=Asia/Shanghai","root","root");
    15.                     }catch (ClassNotFoundException e){
    16.                         e.printStackTrace();
    17.                     }catch (SQLException ex){
    18.                         ex.printStackTrace();
    19.                     }
    20.                 }
    21.             }
    22.         }
    23.         return connection;
    24.     }
    25. }
    1. /**
    2.  * 统一的增删改查
    3.  */
    4. public interface BaseService {
    5.  
    6.     //查
    7.     List queryData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException, InstantiationException;
    8.  
    9.     //改
    10.     int updateData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException;
    11.  
    12.     //删
    13.     int deleteData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException;
    14. }
    1. public class BaseServiceImpl implements BaseService {
    2.  
    3.     private Connection connection = DBUtil.getConnection();
    4.  
    5.     private GenSQLProvider genSQLProvider = new GenSQLProvider();
    6.  
    7.     //查询后结果需要通过反射把值设置进去
    8.     public List queryData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException, InstantiationException {
    9.         ArrayList result = new ArrayList();
    10.  
    11.         //拿到泛型的类类型，不要new对象获取，太low了，用反射
    12.         ParameterizedType type = (ParameterizedType) this.getClass().getGenericSuperclass();
    13.         Class repoClazz = (Class)type.getActualTypeArguments()[0];
    14.  
    15.         String sql = genSQLProvider.genQuerySQL(obj);
    16.         Statement statement = connection.createStatement();
    17.         ResultSet resultSet = statement.executeQuery(sql);
    18.         while(resultSet.next()){
    19.             //拿到泛型的类类型，不要new对象获取，太low了，用反射
    20.             Object instance = repoClazz.newInstance();
    21.             Field[] fields = repoClazz.getDeclaredFields();
    22.             for (Field field : fields) {
    23.                 TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    24.                 String columnKey;
    25.                 //扩展：没有注解也给映射
    26.                 Object fieldRes;
    27.                 if(null!= tableColumn){
    28.                     columnKey = tableColumn.dbColumn();
    29.                 }else {
    30.                     columnKey = field.getName();  //没有则用字段的名字做列
    31.                 }
    32.                 try {
    33.                     fieldRes = resultSet.getObject(columnKey, field.getType());
    34.                 }catch (SQLException e){
    35.                     continue;
    36.                 }
    37.                 String setterName = "set" + field.getName().substring(0,1).toUpperCase() + field.getName().substring(1);
    38.                 repoClazz.getMethod(setterName,field.getType()).invoke(instance,fieldRes);  //相当于instance.setxxx(fieldRes);
    39.             }
    40.             result.add((T)instance);
    41.         }
    42.         return result;
    43.     }
    44.  
    45.     public int updateData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException {
    46.         String sql = genSQLProvider.genUpdateSQL2(obj);
    47.         Statement statement = connection.createStatement();
    48.         return statement.executeUpdate(sql);
    49.     }
    50.  
    51.     public int deleteData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException {
    52.         String sql = genSQLProvider.genDeleteSQL(obj);
    53.         Statement statement = connection.createStatement();
    54.         return statement.executeUpdate(sql);
    55.     }
    56. }
    1. /**
    2.  * 对OrderInfo对象生成sql语句
    3.  */
    4. public class GenSQLProvider {
    5.  
    6.     //select xxx,xxx from table where xxx = 'xxx' and xxx = 'xxx' order by xxx desc|asc
    7.     public String genQuerySQL(Object obj) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    8.         StringBuffer sql = new StringBuffer("select ");
    9.         StringBuffer paramSql = new StringBuffer();
    10.         StringBuffer whereSql = new StringBuffer(" where 1=1 ");
    11.  
    12.         Class clazz = obj.getClass();
    13.         Table table = clazz.getAnnotation(Table.class);
    14.         if (table == null) {
    15.             System.out.println("no table");
    16.         }
    17.         //拿到表名和排序字段和顺序
    18.         String tableName = table.tableName();
    19.         String order = table.order();
    20.         String orderBy = table.orderBy();
    21.  
    22.         Field[] fields = clazz.getDeclaredFields();
    23.         for (Field field : fields) {
    24.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    25.             if (tableColumn != null) {
    26.                 paramSql.append(tableColumn.dbColumn()).append(",");
    27.             }
    28.             String getterName = "get" + field.getName().substring(0, 1).toUpperCase() + field.getName().substring(1);
    29.             Object fieldValue = clazz.getMethod(getterName).invoke(obj);//相当于orderInfo.getOrderId();
    30.             if(null==fieldValue || StringUtils.isEmpty(field.toString())){
    31.                 continue;
    32.             }
    33.             fieldValue = getColumnType(field, fieldValue);
    34.             whereSql.append(" and ").append(tableColumn.dbColumn()).append(" = ").append(fieldValue);
    35.         }
    36.  
    37.         sql.append(paramSql.substring(0, paramSql.length() - 1)).append(" from ").append(tableName).append(whereSql);
    38.         if (!StringUtils.isEmpty(orderBy)) {
    39.             sql.append(" order by ").append(orderBy);
    40.             if (!StringUtils.isEmpty(order)) {
    41.                 sql.append(" " + order);
    42.             }
    43.         }
    44.         return sql.toString();
    45.     }
    46.     private Object getColumnType(Field field, Object fieldValue) {
    47.         //参数类型转换
    48.         if (field.getType() == String.class) {
    49.             fieldValue = "'" + fieldValue + "'";
    50.         } else if (field.getType() == int.class || field.getType() == Integer.class) {
    51.             //...各种类型转换
    52.         }
    53.         return fieldValue;
    54.     }
    55. }

    遗留问题：

    ①异常处理

    ②数据库链接参数配置项 --整合MyBatis，主要是集成参数类型转换功能。

    2.2整合MyBatis

    复写Service实现

    1. /**
    2.  * 传入的Bean对象
    3.  * 不创建对象而使用HasHMap传参是因为会有分页需求，获取版本号之类的
    4.  */
    5. @Component
    6. public class MBBaseServiceImpl implements BaseService {
    7.  
    8.     @Autowired
    9.     BaseMapper baseMapper;
    10.     //TODO:https://www.bilibili.com/video/BV1hd4y1d788?p=14&spm_id_from=pageDriver&vd_source=85a097599612a3ab01f6d380f0d6b0ef
    11.  
    12.     @Override
    13.     public List queryData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException, InstantiationException {
    14.         ArrayList result = new ArrayList<>();
    15.  
    16.         //拿到要操作Bean对象的类型，repoClazz代表T的具体类型（OrderInfo.class）
    17.         ParameterizedType type = (ParameterizedType) this.getClass().getGenericSuperclass();
    18.         Class repoClazz = (Class) type.getActualTypeArguments()[0];
    19.  
    20.         //具体参数的类型
    21.         Class objClazz = obj.getClass();
    22.  
    23.         Map paramMap = new HashMap<>();
    24.         Field[] fields = objClazz.getDeclaredFields();
    25.         for (Field field : fields) {
    26.             String getterName = "get" + field.getName().substring(0, 1).toUpperCase() + field.getName().substring(1);
    27.             Object fieldValue = obj.getClass().getMethod(getterName).invoke(obj);
    28.             if (null != fieldValue) {
    29.                 paramMap.put(field.getName(), fieldValue);
    30.             }
    31.         }
    32.         List> queryData = baseMapper.selectData(paramMap, repoClazz);
    33.         //通过反射来做封装，将Map封装成T实例
    34.         for (Map data : queryData) {
    35.             Object instance = repoClazz.newInstance();
    36.             Field[] fields2 = repoClazz.getDeclaredFields();
    37.             for (Field field2 : fields2) {
    38.                 TableColumn tableColumn = field2.getAnnotation(TableColumn.class);
    39.                 String columnKey;
    40.                 Object fieldsRes;
    41.                 if (null != tableColumn) {
    42.                     columnKey = tableColumn.dbColumn();
    43.                 } else {
    44.                     columnKey = field2.getName();
    45.                 }
    46.                 //TODO 要异常处理
    47.                 fieldsRes = data.get(columnKey);
    48.  
    49.                 String setterName = "set" + field2.getName().substring(0, 1) + field2.getName().substring(1);
    50.                 repoClazz.getMethod(setterName, field2.getType()).invoke(instance, (Integer)fieldsRes);
    51.             }
    52.             result.add((T) instance);
    53.         }
    54.         return result;
    55.     }
    56.  
    57.     @Override
    58.     public int updateData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException {
    59.         //拿到要操作Bean对象的类型，repoClazz代表T的具体类型（OrderInfo.class）
    60.         ParameterizedType type = (ParameterizedType) this.getClass().getGenericSuperclass();
    61.         Class repoClazz = (Class) type.getActualTypeArguments()[0];
    62.  
    63.         //具体参数的类型
    64.         Class objClazz = obj.getClass();
    65.  
    66.         Map param = new HashMap<>();
    67.         Field[] fields = objClazz.getDeclaredFields();
    68.         for (Field field : fields) {
    69.             Object fieldValue = ReflectUtil.getValue(obj, field);
    70.             if (null != fieldValue) {
    71.                 param.put(field.getName(), fieldValue);
    72.             }
    73.         }
    74.         return baseMapper.updateData(param, repoClazz);
    75.     }
    76.  
    77.     @Override
    78.     public int deleteData(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, SQLException {
    79.         ParameterizedType type = (ParameterizedType) this.getClass().getGenericSuperclass();
    80.         Class repoClazz = (Class) type.getActualTypeArguments()[0];
    81.  
    82.         Class objClazz = obj.getClass();
    83.  
    84.         Map param = new HashMap<>();
    85.         Field[] fields = objClazz.getDeclaredFields();
    86.         for (Field field : fields) {
    87.             Object fieldValue = ReflectUtil.getValue(obj, field);
    88.             if (null != fieldValue) {
    89.                 param.put(field.getName(), fieldValue);
    90.             }
    91.         }
    92.         int i = baseMapper.deleteData(param, repoClazz);
    93.         return i;
    94.     }
    95. }
    1. public interface BaseMapper {
    2.  
    3.     /**
    4.      * @UpdateProvider：动态生成sql，不用在xml中写。type：指定生成的类。method：指定那个方法生成的
    5.      * @param param：传入参数
    6.      * @param repo：操作对象
    7.      * @return
    8.      */
    9.     @UpdateProvider(type = MySqlProvider.class, method = "genUpdateSql")
    10.     public Integer updateData(@Param("requestData") Map param, @Param("repoClass") Class repo);
    11.  
    12.     @DeleteProvider(type = MySqlProvider.class, method = "genDeleteSql")
    13.     public Integer deleteData(@Param("requestData") Map param, @Param("repoClass") Class repo);
    14.  
    15.     @SelectProvider(type = MySqlProvider.class, method = "genSelectSql")
    16.     public List> selectData(@Param("requestData") Map param, @Param("repoClass") Class repo);
    17. }
    1. public class MySqlProvider {
    2.  
    3.     public String genUpdateSql(Map param) {
    4.         Map paramMap = (Map) param.get("requestData");
    5.         Class repoClass = (Class) param.get("repoClass");
    6.  
    7.         Table table = repoClass.getAnnotation(Table.class);
    8.         String tableName = table.tableName();
    9.  
    10.         //update table set col1 = #{requestData.attr1},col2=#{requestData.attr2} where orderId = #{request.orderId}
    11.         SQL sql = new SQL();
    12.         Field[] fields = repoClass.getDeclaredFields();
    13.         for (Field field : fields) {
    14.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    15.             if (null == tableColumn) {
    16.                 continue;
    17.             }
    18.             if (paramMap.containsKey(field.getName()) && StringUtils.isEmpty(tableColumn.isPK())) {
    19.                 sql.SET(tableColumn.dbColumn() + "= #{requestData." + field.getName() + "}");
    20.             }
    21.             if (!StringUtils.isEmpty(tableColumn.isPK())) {
    22.                 sql.WHERE(tableColumn.dbColumn() + " = #{requestData." + field.getName() + "}");
    23.                 continue;
    24.             }
    25.         }
    26.         sql.UPDATE(tableName);
    27.         System.out.println(sql.toString());
    28.         return sql.toString();
    29.     }
    30.  
    31.     public String genDeleteSql(Map param) {
    32.         Map paramMap = (Map) param.get("requestData");
    33.         Class repoClass = (Class) param.get("repoClass");
    34.  
    35.         Table table = repoClass.getAnnotation(Table.class);
    36.         String tableName = table.tableName();
    37.  
    38.         //delete from order_info where orderId = #{requestData.orderId}
    39.         SQL sql = new SQL();
    40.         Field[] fields = repoClass.getDeclaredFields();
    41.         for (Field field : fields) {
    42.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    43.             if (null == tableColumn) {
    44.                 continue;
    45.             }
    46.             if (!StringUtils.isEmpty(tableColumn.isPK())) {
    47.                 sql.WHERE(tableColumn.dbColumn() + " = #{requestData." + field.getName() + "}");
    48.                 break;
    49.             }
    50.         }
    51.         sql.DELETE_FROM(tableName);
    52.         System.out.println(sql.toString());
    53.         return sql.toString();
    54.     }
    55.  
    56.     public String genSelectSql(Map param) {
    57.         Map paramMap = (Map) param.get("requestData");
    58.         Class repoClass = (Class) param.get("repoClass");
    59.  
    60.         Table table = repoClass.getAnnotation(Table.class);
    61.         String tableName = table.tableName();
    62.  
    63.  
    64.         //select ***,*** from order_info where xxx = #{xxx} and xxx = #{xxx} order by xxx desc|asc
    65.         SQL sql = new SQL();
    66.         Field[] fields = repoClass.getDeclaredFields();
    67.         for (Field field : fields) {
    68.             TableColumn tableColumn = field.getAnnotation(TableColumn.class);
    69.             if (null == tableColumn) {
    70.                 continue;
    71.             }
    72.             sql.SELECT(tableColumn.dbColumn());
    73.             if (paramMap.containsKey(field.getName())) {
    74.                 sql.WHERE(tableColumn.dbColumn() + " = #{requestData." + field.getName() + "}");
    75.             }
    76.         }
    77.         sql.FROM(tableName);
    78.         if (!StringUtils.isEmpty(table.orderBy())) {
    79.             sql.ORDER_BY(table.orderBy());
    80.             if (!StringUtils.isEmpty(table.order())) {
    81.                 //添加排序顺序
    82.             }
    83.         }
    84.         System.out.println(sql.toString());
    85.         return sql.toString();
    86.     }
    87. }
    1. @RunWith(SpringRunner.class)
    2. @SpringBootTest
    3. public class AnnoDemoTest {
    4.     @Autowired
    5.     OrderInfoService orderInfoService;
    6.  
    7.     @Test
    8.     public void queryData() throws Exception {
    9.         OrderInfo orderInfo = new OrderInfo();
    10.         orderInfo.setOrderId(10003);
    11.         orderInfo.setClientName("xuyu");
    12.  
    13. //        int i = orderInfoService.deleteData(orderInfo);
    14. //        System.out.println(i);
    15.  
    16. //        int j = orderInfoService.updateData(orderInfo);
    17. //        System.out.println(j);
    18.  
    19.         List orderInfos = orderInfoService.queryData(orderInfo);
    20.         for (OrderInfo info : orderInfos) {
    21.             System.out.println(info);
    22.         }
    23.     }
    24. }

    3.自动生成

    POJO属性类型有要求，必须与JDBC的返回结果一致。实现将采用自动生成的方式来生成POJO对象。

    1.怎么拿到数据库的表结构？（通过JDBC连接获取）

    1. /**
    2.  * 通过JDBC连接获取数据库表结构
    3.  */
    4. public class JDBCTest {
    5.     public static void main(String[] args) throws ClassNotFoundException, SQLException {
    6.         Class.forName("com.mysql.cj.jdbc.Driver");
    7.         Properties properties = new Properties();
    8.         properties.put("user", "root");
    9.         properties.put("password", "root");
    10.         properties.put("userInformationSchema", "true"); //加上这个参数就可以从jdbc连接中获取我们想要的结果
    11.         Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test?characterEncoding=utf8&serverTimezone=Asia/Shanghai",
    12.                 properties);
    13.         DatabaseMetaData meta = connection.getMetaData();
    14.         System.out.println("==================映射表结构============");
    15.         ResultSet tables = meta.getTables("test", "%", "order_info", new String[]{"TABLE"});  //拿到对应的表;参数：库名，全匹配，表名
    16.         while (tables.next()) {
    17.             ResultSetMetaData metaData = tables.getMetaData();
    18.             String table_name = tables.getString("TABLE_NAME");  //拿到表名
    19.             String remarks = tables.getString("REMARKS");  //拿到备注
    20.             System.out.println("Number for Column:" + metaData.getColumnCount());  //拿到对应列
    21.             for (int i = 1; i < metaData.getColumnCount(); i++) {
    22.                 int metaType = metaData.getColumnType(i);
    23.                 String metaName = metaData.getColumnName(i);
    24.             }
    25.         }
    26.         System.out.println("==================映射列结构============");
    27.         ResultSet columns = meta.getColumns("test", "%", "order_info", "%");//拿到对应列，参数，同上 + 列的全匹配
    28.         while (columns.next()) {
    29.             String column_name = columns.getString("COLUMN_NAME");//列名
    30.             String type_name = columns.getString("TYPE_NAME");//类型
    31.             int column_size = columns.getInt("COLUMN_SIZE");//列大小
    32.             int decimal_digits = columns.getInt("DECIMAL_DIGITS");//小数点后位数
    33.             int nullable = columns.getInt("NULLABLE");//是否为空
    34.             String remarks = columns.getString("REMARKS");//注解
    35.             System.out.println(column_name + " " + type_name + " " + column_size + " " + decimal_digits + " " + nullable + " " + remarks);
    36.         }
    37.         System.out.println("==================映射主键信息============");
    38.         ResultSet primaryKeys = meta.getPrimaryKeys("test", "%", "order_info");
    39.         while (primaryKeys.next()){
    40.             ResultSetMetaData metaData = primaryKeys.getMetaData();
    41.             int columnCount = metaData.getColumnCount();
    42.             for (int i = 1; i < columnCount; i++) {
    43.                 System.out.println(metaData.getColumnName(i) + " " + primaryKeys.getString(metaData.getColumnName(i)));
    44.             }
    45.         }
    46.     }
    47. }

    2.怎么生成POJO？（①使用StringBuffer拼凑完成的java代码通过流方式实现-MyBatis实现，②freemarker模板引擎）

    https://gitee.com/xuyu294636185/AnnoDemo.git

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  • 原文地址：https://blog.csdn.net/xy294636185/article/details/126813661