使用通配符从多个jar加载资源

Question

I have a Java application with multiple modules, each module has a jar file. each jar file follows same folder structure called META-INF/props Is there a way in java to load all the property files which are in `META-INF/props of multiple jars using a wild card?

Something like

ClassLoader.getSystemResourceAsStream("META-INF/props/*.properties");

I know that this method does not accept wild cards and does not return array of streams , but is it possible to do something like this?

Answer 1

No, there is no standard/reliable way to do this. Some libraries take advantage of common patterns of ClassLoader.getResources implementations (specifically, that they usually always return "file:" or "jar:file:" URLs) in order to support wildcards in resource lookups. For example, the Wildcards in application context constructor resource paths explains how Spring does this, and it lists several caveats ("Implications on portability", "Classpath*: portability", "notes relating to wildcards").

Answer 2

I wrote some code to get around this this limitation.

I read all entries from class path and determine if it is a folder or a JAR file and then look for the entries in "META_INF/props". If the entry is a property, I load it.

Below is the code, it is not refined but it gives general idea.

try{
    URL[] urls = ((URLClassLoader) LoaderTest.class.getClassLoader()).getURLs();
    HashMap<String, Properties> mapProperties = new HashMap<String, Properties>();

    for(URL url: urls){
        File file = new File(url.getFile());
        if(file.isDirectory()){
            System.out.println("Directory: " +file.getName());
            File propFolder = new File(file.getAbsolutePath() + "/META-INF/props");
            if (propFolder.exists() && propFolder.isDirectory()){
                for(File f: propFolder.listFiles()){
                    if(f.getName().endsWith("properties") || f.getName().endsWith("props")){
                        Properties props = new Properties();
                        props.load(new FileReader(f));
                        String appName = props.getProperty("load.global.props.appName");
                        if(appName != null){
                            if( mapProperties.get(appName) == null) {
                                mapProperties.put(appName, props);
                            } else {
                                mapProperties.get(appName).putAll(props);
                            }
                        }
                    }
                }
            }
        } else if (file.getName().endsWith("jar")){
            System.out.println("Jar File: " + file.getName());
            JarFile jarFile = null; 
            try{
                jarFile = new JarFile(file);
                Enumeration<JarEntry> entries = jarFile.entries();
                while ( entries.hasMoreElements() ){
                    JarEntry entry = entries.nextElement();
                    if ( entry.getName().startsWith("META-INF/props") && 
                            (entry.getName().endsWith("properties") ||
                            entry.getName().endsWith("props"))){
                        System.out.println("Prop File: " + entry.getName());
                        Properties props = new Properties();
                        props.load(jarFile.getInputStream(entry));
                        String appName = props.getProperty("load.global.props.appName");
                        if(appName != null){
                            if( mapProperties.get(appName) == null) {
                                mapProperties.put(appName, props);
                            } else {
                                mapProperties.get(appName).putAll(props);
                            }

                        }
                    }
                }
            } finally {
                if ( jarFile != null ) jarFile.close();
            }
        }
    }

} catch(Exception e){
    e.printStackTrace();
}