如何从其他 JAR 文件加载资源

Question

我无法从其他运行的 jar 加载资源。这是我的设置

resource.jar  # contains resources I want to load
`-res/hwview/file1

engine.jar    # my application which need resources
`-res/hwview/file2

有趣的是，使用下面的代码我可以加载 file2（在我运行的 jar 中），但不能加载 file1。

String dir = "res/hwview";
Enumeration<URL> e = getClass().getClassLoader().getResources(dir);
while(e.hasMoreElements()) {
    // prints only file1 from engine.jar 
    // (actually it's in classes directory because I run it from my IDE)
    System.out.println(e.nextElement());
}

[OUTPUT]
/path/to/my/project/SiHwViewUiModel/classes/res/hwview

所以我想也许这个 jar 没有被 ClassLoader 拾取，所以我打印了加载的内容

ClassLoader cl = ClassLoader.getSystemClassLoader();
URL[] urls = ((URLClassLoader)cl).getURLs();
for(URL url: urls){
    System.out.println(url.getFile());
}

[OUTPUT]
/path/to/my/project/SiHwViewUiModel/classes/
/path/to/my/project/Resources/deploy/resources.jar
... and other not so important jars

有什么想法吗？ 感谢您的帮助！

Answer 1

我找到了解决方案。 getResources() 方法和类似方法的问题是不能给定目录，而只能给定一个特定的文件。这意味着如果我想在整个类路径中搜索特定结构，我需要在基目录中创建 marker 文件。

示例：我想进入my/path目录->创建marker.info（名称无关紧要）文件然后搜索。

resources.jar
`- my/path/
   |- my/directories
   `- marker.info

resources2.jar
`- my/path/
   |- my/other/directories
   `- marker.info

# search
Enumeration<URL> urls = getClass().getClassLoader().getResources("my/path/marker.info"); 

# print
print(urls);
/path/to/resources.jar!/my/path/marker.info
/path/to/resources2.jar!/my/path/marker.info

Answer 2

如果 JAR 文件位于类路径中，则无需执行任何特殊操作。将找到资源。

如果它们不在类路径中，您需要创建一个URLClassLoader 并使用它的getResource() 方法。

Answer 3

在Spring中，它可以从classpath中的所有jar文件中加载xml文件：

ApplicationContext context = new ClassPathXmlApplicationContext(
        "classpath*:**/applicationContext*.xml");

您可以查看 Spring 源代码以了解 Spring 是如何实现的。

Answer 4

public final class JarResource
{
private String jarFileName;
private Map<String, Long> hashSizes = new HashMap<String, Long>();
private Map<String, Object> hashJarContents = new HashMap<String, Object>();

public JarResource(String jarFileName) throws Exception
{
    this.jarFileName = jarFileName;
    ZipFile zipFile = new ZipFile(this.jarFileName);

    Enumeration<ZipEntry> e = (Enumeration<ZipEntry>) zipFile.entries();
    while (e.hasMoreElements())
    {
        ZipEntry zipEntry = e.nextElement();
        if(!zipEntry.isDirectory())
        {
            hashSizes.put(getSimpleName(zipEntry.getName()), zipEntry.getSize());
        }
    }
    zipFile.close();

    // extract resources and put them into the hashMap.
    FileInputStream fis = new FileInputStream(jarFileName);
    BufferedInputStream bis = new BufferedInputStream(fis);
    ZipInputStream zis = new ZipInputStream(bis);
    ZipEntry ze = null;

    while ((ze = zis.getNextEntry()) != null)
    {
        if (ze.isDirectory())
        {
            continue;
        }
        else
        {
            long size = (int) ze.getSize();
            // -1 means unknown size.
            if (size == -1)
            {
                size = hashSizes.get(ze.getName());
            }

            byte[] b = new byte[(int) size];
            int rb = 0;
            int chunk = 0;
            while (((int) size - rb) > 0)
            {
                chunk = zis.read(b, rb, (int) size - rb);
                if (chunk == -1)
                {
                    break;
                }
                rb += chunk;
            }

            hashJarContents.put(ze.getName(), b);
        }
    }
    zis.close();
}

public byte[] getResource(String name)
{
    return (byte[]) hashJarContents.get(name);
}

private String getSimpleName(String entryName)
{
    // Remove ".jar" extension
    int index = entryName.indexOf("/");
    String fileNameWithoutExt = entryName.substring(index, entryName.length());

    return fileNameWithoutExt;
}
}

然后使用这个类来加载你的资源：

public static void main(String[] args) throws Exception
{
    JarResource jr = new JarResource("/home/mjiang/Downloads/solr-4.8.0/dist/solr-cell-4.8.0-test.jar");
    byte[] resource = jr.getResource("/META-INF/NOTICE.txt");

    InputStream input = new ByteInputStream(resource, resource.length);

    BufferedReader dis = new BufferedReader(new InputStreamReader(input));

    String line = "";
    while((line = dis.readLine()) != null)
    {
        System.out.println(line);
    }

    dis.close();
}