从另一个jar文件访问资源 [英] Access resources from another jar file

问题描述

我有一个简单的结构:一个包含大量数据的数据jar文件，以及一个使用数据运行服务的服务jar文件.为了使数据易于替换，我将它们分开，并且service.jar的类路径包含data.jar所在的目录.

I have a simple structure: A data jar file which contains a batch of data, and a service jar file, which runs a service using the data. To make the data easy to replace, I have them separate, and service.jar's classpath contains the directory which data.jar is in.

在service.jar中，我使用getResource加载数据文件.如果数据文件直接位于文件夹中，则有效，但是当它们位于data.jar中时会失败；

Within service.jar, I use getResource to load the data files. This works if the data files are directly within the folder, but fails when they are inside data.jar;

此操作失败:

all
+ globalclasspath
| + data.jar
|   + mine.properties
+ daemons
  + service.jar

jsvc -cp globalclasspath:daemons/service.jar (...)

MyClass.class.getClassLoader( ).getResource( "mine.properties" ); // <-- null

但这可行:

all
+ globalclasspath
| + mine.properties
+ daemons
  + service.jar

jsvc -cp globalclasspath:daemons/service.jar (...)

MyClass.class.getClassLoader( ).getResource( "mine.properties" ); // <-- not null

我不想更改类路径(除非我可以将其更改为不依赖于数据jar文件名称的通用名称)，但是我可以更改getResource字符串(我已经尝试了/data/mine.properties和/data.jar/mine.properties都没有用).我可以做些更改，以便可以从jar中加载资源吗?

I don't want to change the classpath (unless I can change it to something generic which doesn't depend on the name of the data jar file), but I'm fine with changing the getResource string (I've tried /data/mine.properties and /data.jar/mine.properties to no avail). Is there a change I can make so that the resources can be loaded from within the jar?

推荐答案

解决方案1 ​​

使用类路径通配符.

jsvc -cp globalclasspath/*:daemons/service.jar (...)

请参阅"如何在类路径中使用通配符来添加多个jar?"

解决方案2

要在类路径上而不是JAR中读取数据，请使用

To read data in JARs not on the classpath, use URLClassLoader. The general algorithm is this:

1. 在globalclasspath目录中找到JAR列表.
2. 从此JAR列表中创建URLClassLoader.
3. 从URLClassLoader实例中查找所需的资源.

1. Find the list of JARs in the globalclasspath directory.
2. Create a URLClassLoader from this list of JARs.
3. Look up the resource you want from the URLClassLoader instance.

要在类路径上找到JAR，我使用了StackOverflow文章"

To find JARs on the classpath, I used ResourceList from the StackOverflow article "Get a list of resources from classpath directory."

public class MyClass {
    /**
     * Creates a {@code URLClassLoader} from JAR files found in the
     * globalclasspath directory, assuming that globalclasspath is in
     * {@code System.getProperty("java.class.path")}.
     */
    private static URLClassLoader createURLClassLoader() {
        Collection<String> resources = ResourceList.getResources(Pattern.compile(".*\\.jar"));
        Collection<URL> urls = new ArrayList<URL>();
        for (String resource : resources) {
            File file = new File(resource);
            // Ensure that the JAR exists
            // and is in the globalclasspath directory.
            if (file.isFile() && "globalclasspath".equals(file.getParentFile().getName())) {
                try {
                    urls.add(file.toURI().toURL());
                } catch (MalformedURLException e) {
                    // This should never happen.
                    e.printStackTrace();
                }
            }
        }
        return new URLClassLoader(urls.toArray(new URL[urls.size()]));
    }

    public static void main(String[] args) {
        URLClassLoader classLoader = createURLClassLoader();
        System.out.println(classLoader.getResource("mine.properties"));
    }
}

我运行了以下命令:

java -cp globalclasspath:daemons/service.jar MyClass

终端输出:

jar:file:/workspace/all/globalclasspath/data.jar!/mine.properties

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