我有一个函数,该函数提供带有给定注释的类的映射
void <A extends Annotation> ImmutableMap<Class<?>, A> find(Class<A> annotation, String packageBase) {
final ClassLoader loader = Thread.currentThread().getContextClassLoader();
return ClassPath.from(loader).getTopLevelClassesRecursive(packageBase).stream()
.filter(x -> x.load().getAnnotation(annotation) != null)
.collect(Collectors.collectingAndThen(Collectors
.toMap(ClassPath.ClassInfo::load, x -> x.load().getAnnotation(annotation)), ImmutableMap::copyOf));
}
我想使通用提供程序具有缓存,如以下示例所示
@Singleton
public class AnnotatedClassProvider {
private final Map<Class<? extends Annotation>, ImmutableMap<Class<?>, Object>> cache;
private final String basePackage;
public AnnotatedClassProvider(String basePackage) {
this.basePackage = basePackage;
this.cache = Maps.newHashMap();
}
public <A extends Annotation> ImmutableMap<Class<?>, A> get(Class<A> annotation) {
ImmutableMap<Class<?>, A> cached = cache.get(annotation);
if (cached != null)
return cached;
final ClassLoader loader = Thread.currentThread().getContextClassLoader();
cached = ClassPath.from(loader).getTopLevelClassesRecursive(basePackage).stream()
.filter(x -> x.load().getAnnotation(annotation) != null)
.collect(Collectors.collectingAndThen(Collectors
.toMap(ClassPath.ClassInfo::load, x -> x.load().getAnnotation(annotation)), ImmutableMap::copyOf));
this.cache.put(annotation, cached);
return (cached);
}
}
我的问题:对于以下地图,我找不到像Object
函数中那样用通用A
替换get
的方法:
private final Map<Class<? extends Annotation>, ImmutableMap<Class<?>, Object>> cache;
编辑:
当我不指定映射泛型时,它将进行编译,但是我必须强制使用get方法。有办法避免这种情况吗?
private final Map<Class<? extends Annotation>, ImmutableMap> cache;
我认为应该看起来像这样
private final <A extends Annotation> Map<Class<A>, ImmutableMap<Class<?>, A>> cache;
参考方案
如果不进行强制转换,这似乎是不可能的,因此以下几行解决了我的问题:
private final Map<Class<? extends Annotation>, ImmutableMap> cache;
public <A extends Annotation> ImmutableMap<Class<?>, A> get(Class<A> annotation) {
@SuppressWarnings("unchecked")
ImmutableMap<Class<?>, A> cached = cache.get(annotation);
...
}
对于有兴趣的人,这就是我的提供者现在的样子
接口
public interface AnnotatedClassProvider {
<A extends Annotation> ImmutableMap<Class<?>, A> get(Class<A> annotation) throws IOException;
}
抽象类
public abstract class AbstractAnnotatedClassProvider implements AnnotatedClassProvider {
private final Map<Class<? extends Annotation>, ImmutableMap> cache;
public AbstractAnnotatedClassProvider() {
this.cache = Maps.newHashMap();
}
protected final <A extends Annotation> ImmutableMap<Class<?>, A> find(Class<A> annotation, @Nullable String basePackage) throws IOException {
@SuppressWarnings("unchecked")
ImmutableMap<Class<?>, A> cached = cache.get(annotation);
if (cached != null)
return cached;
ClassPath classPath = ClassPath.from(Thread.currentThread().getContextClassLoader());
ImmutableSet<ClassPath.ClassInfo> set = basePackage == null
? classPath.getAllClasses()
: classPath.getTopLevelClasses(basePackage);
cached = set.stream()
.filter(x -> x.load().getAnnotation(annotation) != null)
.collect(Collectors.collectingAndThen(Collectors
.toMap(ClassPath.ClassInfo::load, x -> x.load().getAnnotation(annotation)), ImmutableMap::copyOf));
this.cache.put(annotation, cached);
return (cached);
}
}
实作
public final class Providers {
public static AnnotatedClassProvider newBased(String basePackage) {
return new AbstractAnnotatedClassProvider() {
@Override
public <A extends Annotation> ImmutableMap<Class<?>, A> get(Class<A> annotation) throws IOException {
return super.find(annotation, basePackage);
}
};
}
public static AnnotatedClassProvider newSimple() {
return new AbstractAnnotatedClassProvider() {
@Override
public <A extends Annotation> ImmutableMap<Class<?>, A> get(Class<A> annotation) throws IOException {
return super.find(annotation, null);
}
};
}
}
例
@Retention(RUNTIME)
@Target(ElementType.TYPE)
public @interface Controller {
String value();
}
package com.test
@Controller("mainController")
public class Main {
public static void main(String[] args) {
AnnotatedClassProvider provider = Providers.newBased("com.test");
Map<Class<?>, Controller> classes = provider.get(Controller.class);
classes.forEach((x, y ) -> System.out.println(String.format("Class: %s annotated with %s with value %s",
x.getName(), y.getClass().getName(), y.value())));
}
}
输出:Class: Main.java annotated with Controller.class with value mainController
感谢所有评论。
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