正如您所注意到的,set()
切入点无法拦截反射场的变化。但是,如果您控制(即可以将方面编织到)调用Field.set*(..)
方法的代码,您也可以通过使用反射来解决该问题。这是一个完整的、可编译的代码示例,说明了该解决方案:
示例注释:
package de.scrum_master.app;
import java.lang.annotation.*;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Serviced {}
带有 main 方法的示例实体类:
package de.scrum_master.app;
public class Person {
@Serviced private int id;
@Serviced private String name;
private String country;
public int getId() { return id; }
public void setId(int id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public String getCountry() { return country; }
public void setCountry(String country) { this.country = country; }
public void setIdReflective(int id) throws Exception {
Person.class.getDeclaredField("id").setInt(this, id);
}
public void setNameReflective(String name) throws Exception {
Person.class.getDeclaredField("name").set(this, name);
}
public void setCountryReflective(String country) throws Exception {
Person.class.getDeclaredField("country").set(this, country);
}
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", country=" + country + "]";
}
public static void main(String[] args) throws Exception {
Person person = new Person();
person.setId(11);
person.setName("Tin Man");
person.setCountry("Oz");
System.out.println("Before reflective setters: " + person);
person.setIdReflective(22);
person.setNameReflective("Cowardly Lion");
person.setCountryReflective("The Land of Oz");
System.out.println("After reflective setters: " + person);
}
}
如您所见,只有三分之二的私有字段具有@Serviced
注释。对所有三个字段调用 Setter 两次:一次正常,一次通过反射。
截取正常和反射场变化的方面:
package de.scrum_master.aspect;
import de.scrum_master.app.Serviced;
import java.lang.reflect.Field;
public aspect ServicedFieldChangeInterceptor {
before(Object newValue):
set(@Serviced private * *) && args(newValue)
{
System.out.println(thisJoinPointStaticPart + " -> " + newValue);
}
before(Object newValue, Field field):
call(public void Field.set*(Object, *)) && args(*, newValue) && target(field)
{
if (field.getAnnotation(Serviced.class) == null)
return;
System.out.println(thisJoinPointStaticPart + " -> " + field + ", " + newValue);
}
}
运行时的示例输出Person.main
:
set(int de.scrum_master.app.Person.id) -> 11
set(String de.scrum_master.app.Person.name) -> Tin Man
Before reflective setters: Person [id=11, name=Tin Man, country=Oz]
call(void java.lang.reflect.Field.setInt(Object, int)) -> private int de.scrum_master.app.Person.id, 22
call(void java.lang.reflect.Field.set(Object, Object)) -> private java.lang.String de.scrum_master.app.Person.name, Cowardly Lion
After reflective setters: Person [id=22, name=Cowardly Lion, country=The Land of Oz]
输出清楚地表明,这两个建议都只对带有注释的字段“做某事”(在这种情况下将信息打印到标准输出)@Serviced
,而跳过其他字段。虽然set()
切入点是静态应用的,但反射式切入点需要动态确定目标字段是否具有匹配的注释。