1.问题
开发过程中,有时需要找到所有classpath下,特定包下某个类的所有子类,如何做到?
2. 实现
比较常见的解决方案是自己遍历目录,查找所有.class文件。
下面这个方法使用spring工具类实现,简化过程,不再需要自己遍历目录
/**
* 获取在指定包下某个class的所有非抽象子类
*
* @param parentClass 父类
* @param packagePath 指定包,格式如"com/sinosun/tarvel"
* @return 该父类对应的所有子类列表
*/
private static <E> List<Class<E>> getSubClasses(final Class<E> parentClass, final String packagePath) throws ClassNotFoundException
{
final ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(false);
provider.addIncludeFilter(new AssignableTypeFilter(parentClass));
final Set<BeanDefinition> components = provider.findCandidateComponents(packagePath);
final List<Class<E>> subClasses = new ArrayList<>();
for (final BeanDefinition component : components)
{
@SuppressWarnings("unchecked") final Class<E> cls = (Class<E>) Class.forName(component.getBeanClassName());
if (Modifier.isAbstract(cls.getModifiers()))
{
continue;
}
subClasses.add(cls);
}
return subClasses;
}
3. 实例
扫描com.sinosun
包下所有CoreStart
类的子类,并采用反射的方式依次查看子类中是否启用数据源。
package com.sinosun.travel.core.main;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
import org.springframework.core.type.filter.AssignableTypeFilter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
/**
* @author caogu
* @date 2019/5/31 13:36
*/
public class DataSourceHandler
{
private static final Logger logger = LoggerFactory.getLogger(DataSourceHandler.class);
private static final String PARENT_PACKAGE= "com.sinosun";
private static final String CORE_START_CLASS_NAME = "com.sinosun.travel.core.main.CoreStart";
private static final String IS_ENABLE_DATA_SOURCE_METHOD_NAME = "isEnableDataSource";
/**
* 根据环境判定是否启用数据源
* 默认不启用数据源;扫描CoreStart类的所有子类,若子类中有一个启用数据源则启用数据源
* @throws Exception 异常
*/
public static void scanIsEnableDataSource() throws Exception
{
List<Class<CoreStart>> coreStartClasses = getSubClasses(CoreStart.class, PARENT_PACKAGE);
logger.info("扫描到CoreStart类的子类有:{}", coreStartClasses);
for (Class<CoreStart> coreStartClass : coreStartClasses)
{
// 只扫描CoreStart的子类,只要一个启用数据源就启用数据源; 默认不启用数据源
// 只检测子类,父类排除
if (!CORE_START_CLASS_NAME.equals(coreStartClass.getName()))
{
Constructor constructor = coreStartClass.getConstructor();
Object obj = constructor.newInstance();
Method[] methods = coreStartClass.getDeclaredMethods();
for (Method method : methods)
{
if (IS_ENABLE_DATA_SOURCE_METHOD_NAME.equals(method.getName()))
{
boolean isEnableDataSource = (boolean) method.invoke(obj);
logger.info("调用{}.{}方法的返回值为{}", coreStartClass.getName(), coreStartClass.getName(), isEnableDataSource);
if (isEnableDataSource)
{
CoreStart.ENABLE_DATA_SOURCE = true;
logger.info("扫描到子类启用数据源,加载数据源!");
return;
}
}
}
}
}
}
/**
* 获取在指定包下某个class的所有非抽象子类
*
* @param parentClass 父类
* @param packagePath 指定包,格式如"com/sinosun/tarvel"
* @return 该父类对应的所有子类列表
*/
private static <E> List<Class<E>> getSubClasses(final Class<E> parentClass, final String packagePath) throws ClassNotFoundException
{
final ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(false);
provider.addIncludeFilter(new AssignableTypeFilter(parentClass));
final Set<BeanDefinition> components = provider.findCandidateComponents(packagePath);
final List<Class<E>> subClasses = new ArrayList<>();
for (final BeanDefinition component : components)
{
@SuppressWarnings("unchecked") final Class<E> cls = (Class<E>) Class.forName(component.getBeanClassName());
if (Modifier.isAbstract(cls.getModifiers()))
{
continue;
}
subClasses.add(cls);
}
return subClasses;
}
public static void main(String[] args)
{
System.out.println(System.getProperty("java.class.path"));
System.out.println(System.getProperty("user.dir"));
}
}
结果如下: