在寫框架時 經常需要掃描classpath指定包路徑下帶有某個Annotation的類，自己整理了一下 封裝成一個工具類了，供大家參考。

原始碼
ClassPathResourceScanner.java 如下：

package com.bytebeats.jupiter.ioc;

import com.bytebeats.jupiter.util.ClassHelper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.io.IOException;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLDecoder;
import java.util.*;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import java.util.regex.Pattern;

/**
* ${DESCRIPTION}
*
* @author Ricky Fung
* @create 2016-12-11 16:02
*/
public class ClassPathCandidateComponentScanner {
private final Logger logger = LoggerFactory.getLogger(getClass());

public static final String CLASS_SUFFIX = ".class";

private static final Pattern INNER_PATTERN = java.util.regex.Pattern.compile("\\$(\\d+).", java.util.regex.Pattern.CASE_INSENSITIVE);

public Set<Class<?>> findCandidateComponents(String packageName) throws IOException {
if (packageName.endsWith(".")) {
packageName = packageName.substring(0, packageName.length()-1);
}
Map<String, String> classMap = new HashMap<>(32);
String path = packageName.replace(".", "/");
Enumeration<URL> urls = findAllClassPathResources(path);
while (urls!=null && urls.hasMoreElements()) {
URL url = urls.nextElement();
String protocol = url.getProtocol();
if ("file".equals(protocol)) {
String file = URLDecoder.decode(url.getFile(), "UTF-8");
File dir = new File(file);
if(dir.isDirectory()){
parseClassFile(dir, packageName, classMap);
}else {
throw new IllegalArgumentException("file must be directory");
}
} else if ("jar".equals(protocol)) {
parseJarFile(url, classMap);
}
}

Set<Class<?>> set = new HashSet<>(classMap.size());
for(String key : classMap.keySet()){
String className = classMap.get(key);
try {
set.add(ClassHelper.forName(className));
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
return set;
}

protected void parseClassFile(File dir, String packageName, Map<String, String> classMap){
if(dir.isDirectory()){
File[] files = dir.listFiles();
for (File file : files) {
parseClassFile(file, packageName, classMap);
}
} else if(dir.getName().endsWith(CLASS_SUFFIX)) {
String name = dir.getPath();
name = name.substring(name.indexOf("classes")+8).replace("\\", ".");
System.out.println("file:"+dir+"\t class:"+name);
addToClassMap(name, classMap);
}
}

protected void parseJarFile(URL url, Map<String, String> classMap) throws IOException {
JarFile jar = ((JarURLConnection) url.openConnection()).getJarFile();
Enumeration<JarEntry> entries = jar.entries();
while (entries.hasMoreElements()) {
JarEntry entry = entries.nextElement();
if (entry.isDirectory()) {
continue;
}
String name = entry.getName();
if(name.endsWith(CLASS_SUFFIX)){
addToClassMap(name.replace("/", "."), classMap);
}
}
}

private boolean addToClassMap(String name, Map<String, String> classMap){

if(INNER_PATTERN.matcher(name).find()){ //過濾掉匿名內部類
System.out.println("anonymous inner class:"+name);
return false;
}
System.out.println("class:"+name);
if(name.indexOf("$")>0){ //內部類
System.out.println("inner class:"+name);
}
if(!classMap.containsKey(name)){
classMap.put(name, name.substring(0, name.length()-6)); //去掉.class
}
return true;
}

protected Enumeration<URL> findAllClassPathResources(String path) throws IOException {
if(path.startsWith("/")){
path = path.substring(1);
}
Enumeration<URL> urls = ClassHelper.getClassLoader().getResources(path);

return urls;
}

}
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使用方法
ClassPathCandidateComponentScanner scanner = new ClassPathCandidateComponentScanner();
//要掃描的包名
String packageName = "com.bytebeats";
//獲取該包下所有的類名稱
Set<Class<?>> set = scanner.findCandidateComponents(packageName);
System.out.println(set.size());
for (Class<?> cls : set){
System.out.println(cls.getName());
}
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這方面已經有一些不錯的開源專案，例如：
reflections：https://github.com/ronmamo/reflections
Scannotation：http://scannotation.sourceforge.net/
---------------------
作者：Ricky_Fung
來源：CSDN
原文：https://blog.csdn.net/top_code/article/details/53574523
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