Java之路（十二）：模拟Hibernate

Hibernate

//模拟Hibernate
public class HibernateMock {

    //模拟保存操作
    public static void save(Object obj) {
        try {
            StringBuilder sql = new StringBuilder();
            //sql.append("INSERT INTO student (name,age) VALUES (?,?)");
            sql.append("INSERT INTO student (");

            StringBuilder columnSql = new StringBuilder();//拼接列的SQL
            StringBuilder placeHolderSql = new StringBuilder();//拼接占位符的SQL
            BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass(),Object.class);
            PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
            for (PropertyDescriptor pd : pds) {
                String propertyName = pd.getName();
                columnSql.append(propertyName).append(",");
                placeHolderSql.append("?").append(",");
            }
            //删除最后一个,
            columnSql.deleteCharAt(columnSql.length()-1);
            placeHolderSql.deleteCharAt(placeHolderSql.length()-1);

            sql.append(columnSql);
            sql.append(") VALUES (");
            sql.append(placeHolderSql);
            sql.append(")");

            System.out.println(columnSql);
            Object[] params = {};
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        HibernateMock.save(new Student());
    }

}

若表名和类名不一致，使用文件映射：

    映射文件：处理表名和类名不同的情况，属性名和列名不同的情况
    <class name = "......Student" table = "t_student">
        <property name = "id" column = "sid"/>
        <property name = "name" column = "sname"/>
        <property name = "age" column = "sage"/>
    </class>

或者使用注解来实现：

    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Table {
        String value();
    }

然后获取对象上的注解和注解里的值：

    String tableName = obj.getClass().getSimpleName();
    Table table = obj.getClass().getAnnotation(Table.class);
    if (table != null) {
        tableName = table.value();
    }