[英]Issue with loading class from jar file represented as byte array
我正在尝试从加载在字节数组上的jar文件创建类的实例。
我收到两个参数:
1. byte []代表具有所需类的jar文件
2.合格的班级名称
当我在本地对其进行测试时,它可以按预期工作,但是当我远程上载具有相同合格类名的完全相同的jar文件时(使用在Tomcat服务器中部署的Spring MVC实现的Web应用程序(用于后端)和AngularJS实现的前端)找不到所需的课程:
抛出java.lang.ClassNotFoundException
事实证明,当我进行调试时,该类加载器已正确调用,但没有从jar加载任何类。
如果有人能说出造成这种差异的原因是什么,或者我如何以其他方式实现此功能,我将不胜感激。
一种加载类并返回其实例的方法:
public static <T> T getInstanceOfLoadedClass(byte[] jarFileBytes, String qualifiedClassName) throws ClassFromJarInstantiationException {
LOGGER.info("Getting instance of class from loaded jar file. Class name: " + qualifiedClassName);
try {
return (T) Class.forName(qualifiedClassName, true, new ByteClassLoader(jarFileBytes)).newInstance();
} catch (InstantiationException | IllegalAccessException | IOException | ClassNotFoundException | NoSuchFieldException e) {
LOGGER.error("Exception was thrown while reading jar file for " + qualifiedClassName + "class.", e);
throw new ClassFromJarInstantiationException(e);
}
}
自定义ByteClassLoader:
public class ByteClassLoader extends ClassLoader {
private static final Logger LOGGER = Logger.getLogger(ByteClassLoader.class);
private final byte[] jarBytes;
private final Set<String> names;
public ByteClassLoader(byte[] jarBytes) throws IOException {
this.jarBytes = jarBytes;
this.names = loadNames(jarBytes);
}
private Set<String> loadNames(byte[] jarBytes) throws IOException {
Set<String> set = new HashSet<>();
try (ZipInputStream jis = new ZipInputStream(new ByteArrayInputStream(jarBytes))) {
ZipEntry entry;
while ((entry = jis.getNextEntry()) != null) {
set.add(entry.getName());
}
}
return Collections.unmodifiableSet(set);
}
@Override
public InputStream getResourceAsStream(String resourceName) {
if (!names.contains(resourceName)) {
return null;
}
boolean found = false;
ZipInputStream zipInputStream = null;
try {
zipInputStream = new ZipInputStream(new ByteArrayInputStream(jarBytes));
ZipEntry entry;
while ((entry = zipInputStream.getNextEntry()) != null) {
if (entry.getName().equals(resourceName)) {
found = true;
return zipInputStream;
}
}
} catch (IOException e) {
LOGGER.error("ByteClassLoader threw exception while reading jar byte stream for resource: "+resourceName, e);
e.printStackTrace();
} finally {
if (zipInputStream != null && !found) {
try {
zipInputStream.close();
} catch (IOException e) {
LOGGER.error("ByteClassLoader threw exception while closing jar byte stream for resource: "+resourceName, e);
e.printStackTrace();
}
}
}
return null;
} }
问题在于,在测试该类时,需要加载的类在一个类加载器中。
希望它可以帮助某人解决此问题,因为它很容易遗漏。
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