利用Java反射机制读取注解

小咪咪 2022-05-14 14:39 265阅读 0赞

java代码：

package ORM;
    
    @SxtTable("tb_student")
    public class SxtStudent {
    	
    	@SxtField(columnName="id", type="int", length=10)
    	private int id;
    	@SxtField(columnName="sname", type="varchar", length=10)
    	private String studentName;
    	@SxtField(columnName="age", type = "int", length=3)
    	private int age;
    	
    	
    	public int getId() {
    		return id;
    	}
    	public void setId(int id) {
    		this.id = id;
    	}
    	public String getStudnet() {
    		return studentName;
    	}
    	public void setStudnet(String studnet) {
    		this.studentName = studnet;
    	}
    	public int getAge() {
    		return age;
    	}
    	public void setAge(int age) {
    		this.age = age;
    	}
    	
    	
    }

自定义注解：

package ORM;
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    import javax.lang.model.element.Element;
    
    @Target(value = ElementType.FIELD) //此注解能用于类 接口 枚举 Annotation类型之前
    @Retention(RetentionPolicy.RUNTIME) //表示此注解可以被反射机制读取
    public @interface SxtField {
    	String columnName();
    	String type();
    	int length();
    }

package ORM;
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    import javax.lang.model.element.Element;
    
    @Target(value = ElementType.TYPE) //此注解能用于类 接口 枚举 Annotation类型之前
    @Retention(RetentionPolicy.RUNTIME) //表示此注解可以被反射机制读取
    public @interface SxtTable {
    	String[] value();
    }

通过class获取注解信息：

package ORM;
    
    import java.lang.annotation.Annotation;
    import java.lang.reflect.Field;
    
    /**
     * 使用反射读取注解信息,模拟处理注解信息的流程
     * @author lenovo
     *
     */
    public class ORM {
    	public static void main(String[] args) {
    		try {
    			Class clazz = Class.forName("ORM.SxtStudent"); //返回一个反射对象
    			Annotation[] annotations = clazz.getAnnotations(); //获得类的全部注解即@SxtTable("tb_student")
    			for(Annotation a: annotations) {
    				System.out.println(a);
    			}
    			//获得类指定的注解
    			SxtTable st = (SxtTable) clazz.getAnnotation(SxtTable.class);
    			System.out.println(st.value());
    			
    			//获得类的属性注解
    			Field f = clazz.getDeclaredField("studentName");
    			SxtField sxtField = f.getAnnotation(SxtField.class);
    			System.out.println(sxtField.columnName() + "--" + sxtField.type() + "--" + sxtField.length());
    	
    			//根据获得的表名, 字段信息, 拼出DDL语句, 使用JDBC执行SQL语句, 在数据库中生成相关的表
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    }

结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdqaWFuNTMw_size_27_color_FFFFFF_t_70][]

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