从POJO访问EJB

Question

是否可以从POJO访问EJB？ 我试过了

@EJB MyClass obj

但这不起作用。

Answer 1

如果您使用可以将任何内容转换为托管组件的JSR-199（Java C ontexts和D ependency I njection），则可以进行注入。 因此，如果您的POJO是CDI托管bean，您可以：

@Inject MyEjb service

没有CDI，您将不得不进行查找。

也可以看看

• Java EE平台的上下文和依赖注入
• Java EE 6中的依赖注入提供了统一的EJB和JSF编程模型
• Java EE 6中的CDI，JSF和依赖注入

Answer 2

可以从POJO访问EJB。 你必须为此进行JNDI查找。

通常，依赖注入，就像您现在尝试的那样，仅适用于托管环境 - 在Servlet和EJB中。

Answer 3

您正在使用的注释要求您的基础结构知道使用该注释进入该字段。 您可能需要使用包装类或手动执行，这实际上取决于您的设置。

Answer 4

我将查看@Inject，因为这听起来像我正在寻找的解决方案但是当我尝试它时它不起作用。 我确信我错过了一些东西，但我试了一会儿却没有得到任何结果。 一个紧迫的截止日期导致我实施下面的帮助程序类，我认为如果他们有类似的问题我会发布给任何人使用。

谢谢你的回复。

public class InjectionHelper {

    private static final String DEPENDENCY_SEPERATOR = "/";

    private static Logger logger = Logger.getLogger(InjectionHelper.class);

    private static Map<Class<?>, Object> dependencies = null;

    private static List<Object> dependenciesList = null;

    private static Context baseContext = null;

    /**
     * Search for the dependency of the specified class.
     */
    public static final <T> T injectDependency(Class<T> dependencyClass){

        //initialise the dependencies
        if(dependenciesList == null){
            dependenciesList = new ArrayList<Object>();
            dependencies = new HashMap<Class<?>, Object>();
            try{
                baseContext = new InitialContext();
                populateDependencies(baseContext, new Stack<String>());
            }
            catch(Exception e){
                logger.error("Error populating dependencies", e);
            }
        }

        //We have seen this dependency before and can get it from the map
        if(dependencies.containsKey(dependencyClass)){
            return (T)dependencies.get(dependencyClass);
        }

        //Not seen the dependency so we must try and find it in the list 
        for(Object o: dependenciesList){
            if(dependencyClass.isInstance(o)){
                dependencies.put(dependencyClass, o);
                return (T)o;
            }
        }

        //We don't have the dependency
        return null;
    }

    /**
     * Traverse the InitialContext and extract all dependencies and store them in the map keyed by their class.
     *  
     * @param lookupNameStack
     */
    private static final void populateDependencies(Context ctx, Stack<String> lookupNameStack) {
        try {
            NamingEnumeration<Binding> list = ctx.listBindings("");

            while (list.hasMore()) {
               Binding item = list.next();

               //Get the name and object for the binding
               String lookupName = item.getName();
               Object objectBinding = item.getObject();

               //If a JavaGlobalJndiNamingObjectProxy this is a dependency we want to store
               if(objectBinding instanceof JavaGlobalJndiNamingObjectProxy){

                   //Based on our current position in the tree get the string representation
                   Iterator<String> lookupNameIterator = lookupNameStack.iterator();
                   String lookupPrefix = "";
                   while(lookupNameIterator.hasNext()){
                       lookupPrefix += lookupNameIterator.next();
                   }

                   //lookup the object and store in the map
                   try{
                       Object obj = baseContext.lookup(lookupPrefix+lookupName);
                       dependenciesList.add(obj);
                       logger.info("Found [" + obj.getClass() + "] Lookup [" + lookupPrefix + lookupName +"]");
                   }
                   catch(Exception e){
                       logger.info("Failed to find Lookup [" + lookupPrefix+lookupName + "]", e);
                   }
               }
               lookupNameStack.push(lookupName+DEPENDENCY_SEPERATOR);

               //If we find a context we can explore that branch
               if (objectBinding instanceof Context) {
                   populateDependencies((Context) objectBinding, lookupNameStack);
               }
               //Now we have traversed the branch we need to remove the last leaf
               lookupNameStack.pop();
           }

        } catch (NamingException ex) {
           logger.info("JNDI failure: ", ex);
        }
    }
}