后端：增加 MyBatis JSONTypeHandler

后端：增加指定商品的促销价格计算
前端：商品详情页，增加促销价格计算

common/common-framework/src/main/java/cn/iocoder/common/framework/mybatis/JSONTypeHandler.java

@@ -0,0 +1,70 @@
+package cn.iocoder.common.framework.mybatis;
+
+import com.alibaba.fastjson.JSON;
+import org.apache.ibatis.type.BaseTypeHandler;
+import org.apache.ibatis.type.JdbcType;
+
+import java.sql.CallableStatement;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+
+/**
+ * TODO 芋艿
+ *
+ * 参考 https://www.cnblogs.com/waterystone/p/5547254.html
+ *
+ * 后续，补充下注释和测试类，以及文章。
+ *
+ * @param <T>
+ */
+public class JSONTypeHandler<T extends Object> extends BaseTypeHandler<T> {
+
+    private Class<T> clazz;
+
+    public JSONTypeHandler(Class<T> clazz) {
+        if (clazz == null) throw new IllegalArgumentException("Type argument cannot be null");
+        this.clazz = clazz;
+    }
+
+    @Override
+    public void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
+        ps.setString(i, this.toJson(parameter));
+    }
+
+    @Override
+    public T getNullableResult(ResultSet rs, String columnName) throws SQLException {
+        return this.toObject(rs.getString(columnName), clazz);
+    }
+
+    @Override
+    public T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
+        return this.toObject(rs.getString(columnIndex), clazz);
+    }
+
+    @Override
+    public T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
+        return this.toObject(cs.getString(columnIndex), clazz);
+    }
+
+    private String toJson(T object) {
+        try {
+            return JSON.toJSONString(object);
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private T toObject(String content, Class<?> clazz) {
+        if (content != null && !content.isEmpty()) {
+            try {
+                return (T) JSON.parseObject(content, clazz);
+            } catch (Exception e) {
+                throw new RuntimeException(e);
+            }
+        } else {
+            return null;
+        }
+    }
+
+}