Spring MessageSource 是否支持多个类路径？

Question

I am designing a plugin system for our web based application using Spring framework. Plugins are jars on classpath. So I am able to get sources such as jsp, see below

ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
Resource[] pages = resolver.getResources("classpath*:jsp/*jsp");

So far so good. But I have a problem with the messageSource. It seems to me that ReloadableResourceBundleMessageSource#setBasename does NOT support multiple class path via the "classpath*:" If I use just "classpath:", I get the messageSource just only from one plugin.

Does anyone have an idea how to register messageSources from all plugins? Does exist such an implementation of MessageSource?

Answer 1

With the solution of @seralex-vi basenames /WEB-INF/messages did not function.

I overwrited the method refreshProperties on the class ReloadableResourceBundleMessageSource wich perform both type of basenames (classpath*: and /WEB-INF/)

public class SmReloadableResourceBundleMessageSource extends ReloadableResourceBundleMessageSource {

private static final String PROPERTIES_SUFFIX = ".properties";

private PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();

@Override
protected PropertiesHolder refreshProperties(String filename, PropertiesHolder propHolder) {
    if (filename.startsWith(PathMatchingResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX)) {
        return refreshClassPathProperties(filename, propHolder);
    } else {
        return super.refreshProperties(filename, propHolder);
    }
}

private PropertiesHolder refreshClassPathProperties(String filename, PropertiesHolder propHolder) {
    Properties properties = new Properties();
    long lastModified = -1;
    try {
      Resource[] resources = resolver.getResources(filename + PROPERTIES_SUFFIX);
      for (Resource resource : resources) {
        String sourcePath = resource.getURI().toString().replace(PROPERTIES_SUFFIX, "");
        PropertiesHolder holder = super.refreshProperties(sourcePath, propHolder);
        properties.putAll(holder.getProperties());
        if (lastModified < resource.lastModified())
          lastModified = resource.lastModified();
      }
    } catch (IOException ignored) { 
    }
    return new PropertiesHolder(properties, lastModified);
}

On the spring-context.xml you must have the classpath*: prefix

<bean id="messageSource" class="SmReloadableResourceBundleMessageSource">
    <property name="basenames">
        <list>
            <value>/WEB-INF/i18n/enums</value>
            <value>/WEB-INF/i18n/messages</value>
            <value>classpath*:/META-INF/messages-common</value>
            <value>classpath*:/META-INF/enums</value>
        </list>
    </property>
</bean>

Answer 2

The issue here is not with multiple classpaths or classloaders, but with how many resources the code will try and load for a given path.

The classpath* syntax is a Spring mechanism, one which allows code to load multiple resources for a given path. Very handy. However, ResourceBundleMessageSource uses the standard java.util.ResourceBundle to load the resources, and this is a much simpler, dumber mechanism, which will load the first resource for a given path, and ignore everything else.

I don't really have an easy fix for you. I think you're going to have to ditch ResourceBundleMessageSource and write a custom implementation of MessageSource (most likely by subclassing AbstractMessageSource ) which uses PathMatchingResourcePatternResolver to locate the various resources and expose them via the MessageSource interface. ResourceBundle isn't going to be much help.

Answer 3

You could do something similar to below - essentially specify each relevant basename explicitly.

 <bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource">
        <property name="basenames">
            <list>
                <value>classpath:com/your/package/source1</value>
                <value>classpath:com/your/second/package/source2</value>
                <value>classpath:com/your/third/package/source3/value>
                <value>classpath:com/your/fourth/package/source4</value>
            </list>
        </property>
    </bean>

Answer 4

As alternative, you could override refreshProperties method from ReloadableResourceBundleMessageSource class like below example:

public class MultipleMessageSource extends ReloadableResourceBundleMessageSource {
  private static final String PROPERTIES_SUFFIX = ".properties";
  private PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();

  @Override
  protected PropertiesHolder refreshProperties(String filename, PropertiesHolder propHolder) {
    Properties properties = new Properties();
    long lastModified = -1;
    try {
      Resource[] resources = resolver.getResources(filename + PROPERTIES_SUFFIX);
      for (Resource resource : resources) {
        String sourcePath = resource.getURI().toString().replace(PROPERTIES_SUFFIX, "");
        PropertiesHolder holder = super.refreshProperties(sourcePath, propHolder);
        properties.putAll(holder.getProperties());
        if (lastModified < resource.lastModified())
          lastModified = resource.lastModified();
      }
    } catch (IOException ignored) { }
    return new PropertiesHolder(properties, lastModified);
  }
}

and use it with spring context configuration like ReloadableResourceBundleMessageSource :

  <bean id="messageSource" class="common.utils.MultipleMessageSource">
    <property name="basenames">
      <list>
        <value>classpath:/messages/validation</value>
        <value>classpath:/messages/messages</value>
      </list>
    </property>
    <property name="fileEncodings" value="UTF-8"/>
    <property name="defaultEncoding" value="UTF-8"/>
  </bean>

I think this should do the trick.

Answer 5

overriding ReloadableResourceBundleMessageSource::calculateFilenamesForLocale may be better. Then, ReloadableResourceBundleMessageSource::getProperties can get PropertiesHolder from cachedProperties

Answer 6

You can take advantage of Java configuration and hierarchical message sources to build a quite simple plugin system. In each pluggable jar drop a class like this:

@Configuration
public class MyPluginConfig {
    @Bean
    @Qualifier("external")
    public HierarchicalMessageSource mypluginMessageSource() {
        ReloadableResourceBundleMessageSource messageSource = new ReloadableResourceBundleMessageSource();
        messageSource.setBasenames("classpath:my-plugin-messages");
        return messageSource;
    }
}

and the corresponding my-plugin-messages.properties files.

In the main application Java config class put something like this:

@Configuration
public class MainConfig {
    @Autowired(required = false)
    @Qualifier("external")
    private List<HierarchicalMessageSource> externalMessageSources = Collections.emptyList();

    @Bean
    public MessageSource messageSource() {
        ReloadableResourceBundleMessageSource rootMessageSource = new ReloadableResourceBundleMessageSource();
        rootMessageSource.setBasenames("classpath:messages");

        if (externalMessageSources.isEmpty()) {
            // No external message sources found, just main message source will be used
            return rootMessageSource;
        }
        else {
            // Wiring detected external message sources, putting main message source as "last resort"
            int count = externalMessageSources.size();

            for (int i = 0; i < count; i++) {
                HierarchicalMessageSource current = externalMessageSources.get(i);
                current.setParentMessageSource( i == count - 1 ? rootMessageSource : externalMessageSources.get(i + 1) );
            }
            return externalMessageSources.get(0);
        }
    }
}

If the order of plugins is relevant, just put @Order annotations in each pluggable message source bean.

Answer 7

As @Jia Feng said an alternative solution overriding ReloadableResourceBundleMessageSource::calculateFilenamesForLocale.

It works on spring 5.x

public class WildcardReloadableResourceBundleMessageSource extends ReloadableResourceBundleMessageSource {

    private static final String PROPERTIES_SUFFIX = ".properties";
    private PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();   
    
    @Override
    protected List<String> calculateFilenamesForLocale(String basename, Locale locale) {
        List<String> filenames = super.calculateFilenamesForLocale(basename, locale);
        List<String> add = new ArrayList<>();
        for (String filename : filenames) {
            try {
                Resource[] resources = resolver.getResources(filename + PROPERTIES_SUFFIX);
                for (Resource resource : resources) {
                    String sourcePath = resource.getURI().toString().replace(PROPERTIES_SUFFIX, "");
                    add.add(sourcePath);
                }
            } catch (IOException ignored) {
            }
        }
        filenames.addAll(add);
        return filenames;
    }
    
}