jdk反射+spring注解实现类似hibernate以类建表功能

Bertha 。 2023-02-16 05:51 117阅读 0赞

### 说明：连接数据库并运行sql步骤没做，此处只为通过类构建出sql语句！！！！主键注解没写 ###

1.定义自定义注解

@Documented
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @Component
    public @interface SxTable {
    
        /**
         *
         * @return 表名
         */
        String value();
    }

/**
     * 属性列名
     *
     * @author qiaofeng
     */
    @Documented
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.FIELD)
    public @interface SxField {
    
        /**
         * 列名
         */
        String columnName();
    
        /**
         * 类型
         */
        String type();
    
        /**
         * 长度
         */
        int length();
    }

@Component必须要加上，不然applicationContext.getBeansWithAnnotation(SxTable.class)会获取不到。

2.定义使用注解的类，下面是两个普普通通的entity，自己自行分开成两个类。

@Data
    @SxTable("sx_student")
    public class SxStudent {
    
        @SxField(columnName = "id", type = "varchar", length = 32)
        private String id;
    
        private String name;
    
        private int number;
    
        @SxField(columnName = "success", type = "tinyint", length = 1)
        private boolean success;
    }
    
    @Data
    @SxTable("sx_school")
    public class SxSchool {
    
        @SxField(columnName = "id", type = "varchar", length = 32)
        private String id;
    
        private String name;
    
        @SxField(columnName = "position", type = "varchar", length = 32)
        private String success;
    }

3.编写处理带有自定义注解的逻辑

/**
     * 获取SxTable注解的类，将其转为sql
     * @author qiaofeng
     */
    @Configuration
    public class MyApplicationContextAware implements ApplicationContextAware {
    
        
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            getAnnotationSxTableAll(applicationContext);
        }
    
    
        private void getAnnotationSxTableAll(ApplicationContext applicationContext){
            Map<String, Object> beansWithAnnotation = applicationContext.getBeansWithAnnotation(SxTable.class);
            for (Map.Entry<String, Object> entry : beansWithAnnotation.entrySet()){
                printSql(entry.getValue().getClass());
            }
        }
    
        private void printSql(Class<?> aClass){
            //获取所有注解
            Annotation[] annotations = aClass.getAnnotations();
            //获取类上的指定注解
            SxTable tableAnnotation = aClass.getAnnotation(SxTable.class);
    
            //获取类属性上的注解
            Field[] declaredFields = aClass.getDeclaredFields();
            if (declaredFields.length == 0){
                return;
            }
            StringBuffer stringBuffer = new StringBuffer("create table " + tableAnnotation.value());
            stringBuffer.append("(");
            for (Field field : declaredFields){
                SxField annotation = field.getAnnotation(SxField.class);
                if (annotation != null){
                    stringBuffer.append(annotation.columnName()).append(" ").append(annotation.type()).append("(").append(annotation.length()).append("),");
                }else {
                    stringBuffer.append(field.getName()).append(" ").append(field.getType()==String.class? "varchar" : "int").append("(").append(255).append("),");
                }
            }
            String sql = stringBuffer.substring(0, stringBuffer.lastIndexOf(",")) + ");";
            System.out.println("创建表的sql为：" + sql);
        }
    
    }

有两种，上面为其中一种，实现ApplicationContextAware接口，程序初始化时，会执行setApplicationContext方法，处理逻辑放在此方法中。

第二种，实现ApplicationListener<ApplicationReadyEvent>接口，处理方式类似，最终也是获取到applicationContext上下文进行操作。

4.效果

![20200608160824615.png][]

## 完毕！！！ ##

[20200608160824615.png]: https://img-blog.csdnimg.cn/20200608160824615.png