[英]JAVA How can i get a method to accept a parent class and all of it's extended classes?
[英]How to get all extended classes without libraries
在我的項目中,我有一個類City
和其他擴展它的類( London
, Paris
...)。 我想在不使用任何外部庫的情況下實例化所有擴展City
的類(City 的所有子類)。
我想避免使用這樣的構造函數手動實例化類:
List<City> cities = new ArrayList<City>();
cities.add( new London() );
cities.add( new California() );
cities.add( new Chicago() );
課程:
public abstract Class City{
public abstract String getName();
}
public Class London{
public String getName(){
return "London";
}
}
public Class Paris{
public String getName(){
return "Paris";
}
}
這是一個解決方案,它可以工作,但您可以添加一些增強功能(使其與間接超類一起工作..),想法是:找到項目目錄中的所有類,迭代這些類並查找擴展給定類的所有類(按名字)。 之后實例化所有這些類:
package x;
import java.util.*;
import java.io.File;
import java.io.IOException;
import java.lang.reflect.*;
import java.net.URL;
public class MyClass {
/**
* Scans all classes accessible from the context class loader which belong to
* the given package and subpackages.
*
* @param packageName The base package
* @return The classes
* @throws ClassNotFoundException
* @throws IOException
*/
private static Class[] getClasses(String packageName) throws ClassNotFoundException, IOException {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
assert classLoader != null;
String path = packageName.replace('.', '/');
Enumeration<URL> resources = classLoader.getResources(path);
List<File> dirs = new ArrayList<File>();
while (resources.hasMoreElements()) {
URL resource = resources.nextElement();
dirs.add(new File(resource.getFile()));
}
ArrayList<Class> classes = new ArrayList<Class>();
for (File directory : dirs) {
classes.addAll(findClasses(directory, packageName));
}
return classes.toArray(new Class[classes.size()]);
}
/**
* Recursive method used to find all classes in a given directory and subdirs.
*
* @param directory The base directory
* @param packageName The package name for classes found inside the base
* directory
* @return The classes
* @throws ClassNotFoundException
*/
private static List<Class> findClasses(File directory, String packageName) throws ClassNotFoundException {
List<Class> classes = new ArrayList<Class>();
if (!directory.exists()) {
return classes;
}
File[] files = directory.listFiles();
for (File file : files) {
if (file.isDirectory()) {
assert !file.getName().contains(".");
classes.addAll(findClasses(file, packageName + "." + file.getName()));
} else if (file.getName().endsWith(".class")) {
// System.out.println(packageName + '.' + file.getName().substring(0, file.getName().length() - 6));
classes.add(
Class.forName(packageName + '.' + file.getName().substring(0, file.getName().length() - 6)));
}
}
return classes;
}
public static void main(String[] args) throws ClassNotFoundException {
List<City> cities = new ArrayList<City>();
List<Class> classes = findClasses(new File("C:\\Users\\za.oussama\\Desktop\\Dossiers\\ws\\xx\\bin\\x"), "x");
// print all class names within the project directory
classes.forEach(System.out::println);
// instanciate the classes who extends the class City :
// you can make it dynamic adding the class name to the method parameter
classes.stream().filter(clas -> clas.getSuperclass().getSimpleName().equals("City")).forEach(cl -> {
try {
City city = (City) cl.getDeclaredConstructor().newInstance();
cities.add(city);
} catch (InstantiationException | IllegalAccessException | IllegalArgumentException
| InvocationTargetException | NoSuchMethodException | SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
});
System.out.println();
cities.forEach(c -> System.out.println(" Instance created from class : " + c.getName()));
}
}
輸出
class x.City
class x.London
class x.MyClass
class x.Paris
Instance created from class : London
Instance created from class : Paris
一些代碼是從另一個堆棧答案和此處復制的: https ://dzone.com/articles/get-all-classes-within-package。
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