java 自定义annotation

最新推荐文章于 2025-08-18 22:47:43 发布

liuyifan789789987987

最新推荐文章于 2025-08-18 22:47:43 发布

阅读量126

点赞数

CC 4.0 BY-SA版权

文章标签： java runtime

本文链接：https://blog.youkuaiyun.com/liuyifan789789987987/article/details/84807299

本文介绍如何使用Java注解来实现动态SQL查询语句的生成，包括@Table和@Column注解的应用，以及反射机制的具体实现方式。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


@Inherited
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Column {
  String value() default "";
}

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


@Inherited  //继承
@Target({ElementType.TYPE})  //TYPE 类 METHOD : 方法
@Retention(RetentionPolicy.RUNTIME) //运行时
@Documented
public @interface Table {
	String value() default "";
}

@Table("tb_test")
public class TestDao {

	@Deprecated
	private String tt;

	@Column("_id")
	private String id;

	@Column("_name")
	private String name;

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

}

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Test {

	/**
	 * 通过注解组装查询条件，生成查询语句
	 */
	public static String assembleSqlFromObj(Object obj) {
		 Table table = obj.getClass().getAnnotation(Table.class);  
	        StringBuffer sbSql = new StringBuffer();  
	        String tableName = table.value();  
	        sbSql.append("select * from " + tableName + " where 1=1 ");  
	        Field[] fileds = obj.getClass().getDeclaredFields();  
	        for (Field f : fileds) {  
	            String fieldName = f.getName();  
	            String methodName = "get" + fieldName.substring(0, 1).toUpperCase()  
	                    + fieldName.substring(1);  
	            try {  
	                Column column = f.getAnnotation(Column.class);  
	                if (column != null) {  
	                    Method method = obj.getClass().getMethod(methodName);  
	                    String value = (String) method.invoke(obj);  
	                    if (value != null && !value.equals("")) {  
	                        if (!isnum(column.value()) && !isnum(value)) {  
	                            // 判断参数是不是 in 类型参数 1,2,3  
	                            if (value.contains(",")) {  
	                                sbSql.append(" and " + column.value() + " in (" + value + ") ");  
	                            } else {  
	                                sbSql.append(" and " + column.value() + " like '%" + value + "%' ");  
	                            }  
	                        } else {  
	                            sbSql.append(" and " + column.value() + "=" + value + " ");  
	                        }  
	                    }  
	                }  
	            } catch (Exception e) {  
	                e.printStackTrace();  
	            }  
	        }  
	        return sbSql.toString();  

	}
	
	public static boolean isnum(String target){
		if(target.toUpperCase().contains("id")){
		  return true;	
		}
		if(target.matches("\\d+")){
			return true;
		}
		return false;
		
	}
	
	

}