q前言：
在工作中看到这个知识点，就顺便参考了百度的一些资料，整理一下，希望以后用的到。
一：理论部分
1.使用场景
写一个MVC框架，需要从包中扫描出组件并注册到容器中，而JDK没有提供现成的从方法，只能自己实现
2.需求
给定一个包名，编程得到该包(和其所有子包)下所有的类文件
3.思路
有的web server在部署运行时会解压jar包，因此class文件会在普通的文件目录下。
如果web server不解压jar包，则class文件会直接存在于Jar包中。
对于前者，只需定位到class文件所在目录，然后将class文件名读取出即可；
对于后者，则需先定位到jar包所在目录，然后使用JarInputStream读取Jar包，得到class类名。
二：程序实现
1.程序目录
2.ClasspathPackageScanner.java
package com.scan; import org.slf4j.Logger;
import org.slf4j.LoggerFactory; import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream; public class ClasspathPackageScanner implements PackageScanner{
private Logger logger = LoggerFactory.getLogger(ClasspathPackageScanner.class);
private String basePackage;
private ClassLoader cl; /**
* 初始化
* @param basePackage
*/
public ClasspathPackageScanner(String basePackage) {
this.basePackage = basePackage;
this.cl = getClass().getClassLoader();
}
public ClasspathPackageScanner(String basePackage, ClassLoader cl) {
this.basePackage = basePackage;
this.cl = cl;
}
/**
*获取指定包下的所有字节码文件的全类名
*/
public List<String> getFullyQualifiedClassNameList() throws IOException {
logger.info("开始扫描包{}下的所有类", basePackage);
return doScan(basePackage, new ArrayList<String>());
} /**
*doScan函数
* @param basePackage
* @param nameList
* @return
* @throws IOException
*/
private List<String> doScan(String basePackage, List<String> nameList) throws IOException {
String splashPath = StringUtil.dotToSplash(basePackage);
URL url = cl.getResource(splashPath); //file:/D:/WorkSpace/java/ScanTest/target/classes/com/scan
String filePath = StringUtil.getRootPath(url);
List<String> names = null; // contains the name of the class file. e.g., Apple.class will be stored as "Apple"
if (isJarFile(filePath)) {// 先判断是否是jar包，如果是jar包，通过JarInputStream产生的JarEntity去递归查询所有类
if (logger.isDebugEnabled()) {
logger.debug("{} 是一个JAR包", filePath);
}
names = readFromJarFile(filePath, splashPath);
} else {
if (logger.isDebugEnabled()) {
logger.debug("{} 是一个目录", filePath);
}
names = readFromDirectory(filePath);
}
for (String name : names) {
if (isClassFile(name)) {
nameList.add(toFullyQualifiedName(name, basePackage));
} else {
doScan(basePackage + "." + name, nameList);
}
}
if (logger.isDebugEnabled()) {
for (String n : nameList) {
logger.debug("找到{}", n);
}
}
return nameList;
} private String toFullyQualifiedName(String shortName, String basePackage) {
StringBuilder sb = new StringBuilder(basePackage);
sb.append('.');
sb.append(StringUtil.trimExtension(shortName));
//打印出结果
System.out.println(sb.toString());
return sb.toString();
} private List<String> readFromJarFile(String jarPath, String splashedPackageName) throws IOException {
if (logger.isDebugEnabled()) {
logger.debug("从JAR包中读取类: {}", jarPath);
}
JarInputStream jarIn = new JarInputStream(new FileInputStream(jarPath));
JarEntry entry = jarIn.getNextJarEntry();
List<String> nameList = new ArrayList<String>();
while (null != entry) {
String name = entry.getName();
if (name.startsWith(splashedPackageName) && isClassFile(name)) {
nameList.add(name);
} entry = jarIn.getNextJarEntry();
} return nameList;
} private List<String> readFromDirectory(String path) {
File file = new File(path);
String[] names = file.list(); if (null == names) {
return null;
} return Arrays.asList(names);
} private boolean isClassFile(String name) {
return name.endsWith(".class");
} private boolean isJarFile(String name) {
return name.endsWith(".jar");
} /**
* For test purpose.
*/
public static void main(String[] args) throws Exception {
PackageScanner scan = new ClasspathPackageScanner("com.scan");
scan.getFullyQualifiedClassNameList();
}
}
3.PackageScanner接口
package com.scan;
import java.io.IOException;
import java.util.List;
public interface PackageScanner {
public List<String> getFullyQualifiedClassNameList() throws IOException;
}
4.StringUtil.java
package com.scan;
import java.net.URL;
public class StringUtil {
private StringUtil() {
}
/**
* "file:/home/whf/cn/fh" -> "/home/whf/cn/fh"
* "jar:file:/home/whf/foo.jar!cn/fh" -> "/home/whf/foo.jar"
*/
public static String getRootPath(URL url) {
String fileUrl = url.getFile();
int pos = fileUrl.indexOf('!');
if (-1 == pos) {
return fileUrl;
}
return fileUrl.substring(5, pos);
}
/**
* "cn.fh.lightning" -> "cn/fh/lightning"
* @param name
* @return
*/
public static String dotToSplash(String name) {
return name.replaceAll("\\.", "/");
}
/**
* "Apple.class" -> "Apple"
*/
public static String trimExtension(String name) {
int pos = name.indexOf('.');
if (-1 != pos) {
return name.substring(0, pos);
}
return name;
}
/**
* /application/home -> /home
* @param uri
* @return
*/
public static String trimURI(String uri) {
String trimmed = uri.substring(1);
int splashIndex = trimmed.indexOf('/');
return trimmed.substring(splashIndex);
}
}5.结果