求泛型的Class

项目开发中为了减少重复代码，常常会使用到Java泛型。有时候就需要求泛型的类型。

GenericFoo.java是基类

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
* Created by li on 2015/10/31.
*/
public abstract class GenericFoo<T> {
protected Logger logger = LoggerFactory.getLogger(this.getClass());

private Class<T> beanClass;

public Class<T> getBeanClass(){
logger.debug("this: " + this.getClass() + "\t Super: " + getClass().getGenericSuperclass());
Type type =getClass().getGenericSuperclass();
//        if (!ParameterizedType.class.isAssignableFrom(type.getClass())) {
//            return null;
//        }
ParameterizedType paraType = (ParameterizedType)getClass().getGenericSuperclass();
logger.debug(type.toString());
beanClass = (Class<T>) paraType.getActualTypeArguments()[0];
logger.debug("beanClass: " + beanClass);
return this.beanClass;
}
}

GenericFooChild.java是子类

public class GenericFooChild<T> extends GenericFoo {

}

编写Junit测试类

import com.cqs.models.user.model.User;
import org.junit.Test;

/**
* Created by li on 2015/10/31.
*/
public class GenericFooChildTest {

private GenericFooChild child = new GenericFooChild();

@Test
public void testGetBeanClass() throws Exception {
child.getBeanClass();
}
}

运行结果



查了一些帖子：子类(GenericFooChild)在集成父类(GenericFoo)时不能还写抽象类，需要传入具体的类别

所以：

需要将GenericFooChild修改为：

import com.cqs.models.user.model.User;

/**
* Created by li on 2015/10/31.
*/
public class GenericFooChild extends GenericFoo<User> {

}

运行结果



还有一个一种办法可以求泛型的类型：

在构造器中，传入具体的泛型类型：

父类修改为【添加含参构造函数，getBeanClass()可以直接返回beanClass】：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
* Created by li on 2015/10/31.
*/
public abstract class GenericFoo<T> {
protected Logger logger = LoggerFactory.getLogger(this.getClass());

private Class<T> beanClass;

public GenericFoo(Class<T> beanClass) {
this.beanClass = beanClass;
}

public Class<T> getBeanClass(){
logger.debug("beanClass: " + beanClass);
return this.beanClass;
}
}

子类和JUnit测试类，也要相应的修改

import com.cqs.models.user.model.User;

/**
* Created by li on 2015/10/31.
*/
public class GenericFooChild extends GenericFoo<User> {

public GenericFooChild(Class<User> beanClass) {
super(beanClass);
}
}

import com.cqs.models.user.model.User;
import org.junit.Test;

/**
* Created by li on 2015/10/31.
*/
public class GenericFooChildTest {

private GenericFooChild child = new GenericFooChild(User.class);

@Test
public void testGetBeanClass() throws Exception {
child.getBeanClass();
}
}

运行结果：



参考：(翻译)反射处理java泛型