1.問題
開發過程中,有時需要找到所有classpath下,特定包下某個類的所有子類,如何做到?
2. 實現
比較常見的解決方案是自己遍歷目錄,查找所有.class文件。
下面這個方法使用spring工具類實現,簡化過程,不再需要自己遍歷目錄
/**
* 獲取在指定包下某個class的所有非抽象子類
*
* @param parentClass 父類
* @param packagePath 指定包,格式如"com/sinosun/tarvel"
* @return 該父類對應的所有子類列表
*/
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. 實例
掃描com.sinosun
包下所有CoreStart
類的子類,並採用反射的方式依次查看子類中是否啓用數據源。
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";
/**
* 根據環境判定是否啓用數據源
* 默認不啓用數據源;掃描CoreStart類的所有子類,若子類中有一個啓用數據源則啓用數據源
* @throws Exception 異常
*/
public static void scanIsEnableDataSource() throws Exception
{
List<Class<CoreStart>> coreStartClasses = getSubClasses(CoreStart.class, PARENT_PACKAGE);
logger.info("掃描到CoreStart類的子類有:{}", coreStartClasses);
for (Class<CoreStart> coreStartClass : coreStartClasses)
{
// 只掃描CoreStart的子類,只要一個啓用數據源就啓用數據源; 默認不啓用數據源
// 只檢測子類,父類排除
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("調用{}.{}方法的返回值爲{}", coreStartClass.getName(), coreStartClass.getName(), isEnableDataSource);
if (isEnableDataSource)
{
CoreStart.ENABLE_DATA_SOURCE = true;
logger.info("掃描到子類啓用數據源,加載數據源!");
return;
}
}
}
}
}
}
/**
* 獲取在指定包下某個class的所有非抽象子類
*
* @param parentClass 父類
* @param packagePath 指定包,格式如"com/sinosun/tarvel"
* @return 該父類對應的所有子類列表
*/
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"));
}
}
結果如下: