自定义注解实现orm框架

曾经终败给现在 2023-06-15 11:02 14阅读 0赞

### 一、首先自定义两个注解，分别是表名映射注解和字段名映射注解 ###

import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    //表明映射注解
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @interface TableName{
    	String value();
    }
    
    //属性映射注解
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    @interface FieldName{
    	String name();
    	int length() default 0;
    	
    }

### 二、定义表对应的实体类 ###

@TableName("student_info")
    public class Student {
    	
    	@FieldName(name="id",length=10)
    	private String id;
    	
    	@FieldName(name="user_name")
    	private String userName;
    	
    	@FieldName(name="user_age")
    	private String userAge;
    	
    }

### 三、使用实体类注解拼成查询sql ###

import java.lang.reflect.Field;
    
    public class Main1 {
    	public static String createSql() throws ClassNotFoundException{
    		StringBuffer sqlBuffer = new StringBuffer();
    		sqlBuffer.append("select ");
    		Class<?> clas= Class.forName("spring.Student");
    		
    		/*
    		 * 获取属性注解值即字段名
    		 */
    		Field[] declaredFields = clas.getDeclaredFields();
    		String[] field = new String[declaredFields.length];
    		for(int i = 0;i<declaredFields.length;i++){
    			FieldName annotation2 = declaredFields[i].getAnnotation(FieldName.class);
    			field[i]=annotation2.name();
    			sqlBuffer.append(annotation2.name());
    			if(i<declaredFields.length-1){
    				sqlBuffer.append(",");
    			}
    		}
    		/*
    		 * 获取类注解值表名
    		 */
    		TableName annotation = clas.getAnnotation(TableName.class);
    		String tableName = "";//表名
    		if(null != annotation){
    			tableName = annotation.value();
    		}
    		sqlBuffer.append(" from "+tableName);
    		return sqlBuffer.toString();
    	}
    	
    	public static void main(String[] args) throws ClassNotFoundException {
    		System.out.println(createSql());
    	}
    }