在POJO外部容器中检索servlet上下文，会话和请求 [英] Retrieving servlet context, session and request in a POJO outside container

问题描述

有没有办法从POJO中检索会话？或者最终从POJO中检索一个bean。

Is there any way to retrieve a session from a POJO? Or ultimately to retrieve a bean from a POJO.

澄清：

基本上我正在创建一个bean一个servlet，我需要从Web容器外部（从POJO）访问该bean的属性。我无法将请求传递给pojo;并且需要请求来检索会话。

Basically I am creating a bean from a servlet and I need to access the properties of that bean from outside of the web container (from a POJO). I cannot pass the request to the pojo; and the request is needed to retrieve the session.

更具体地说，我有一个Web应用程序，它使用Cactus框架从Web界面运行JUnit测试。但是，调用JUnit测试运行器的servlet是在jar中编译的;我添加了额外的下拉菜单来更改JUnit测试将从中读取的设置以在不同环境（WLI集群）之间切换，因此，如果已经编译了运行器servlet，我无法修改它以处理来自多个环境的额外参数。我已经尝试了写入.dat文件的持久性方法，JUnit测试将通过Reader类读取该文件;我也尝试过最终无法通过JUnit测试访问的bean方法。

More specifically I have a web application that uses the Cactus framework to run JUnit tests from a web interface. However the servlet that invokes the JUnit test runner is compiled in a jar; I added extra drop down menus to change settings from which the JUnit test will read from to switch between different environments (WLI clusters), so given that the runner servlet is already compiled I cannot modify it to handle the extra parameters from the multiple environments. I have tried the persistence approach of writing to a .dat file fro which the JUnit test will read from by way of a Reader class; also I have have tried the bean approach which ultimately was not accessible from the JUnit test.

推荐答案

仅当你的POJO是在运行 HttpServletRequest 的相同线程中运行，然后您将能够在 ThreadLocal< T> 。

Only and only if your POJO is running in the same thread as the HttpServletRequest is running in, then you'll be able to achieve this with help of ThreadLocal<T>.

创建以下课程：

public final class YourContext implements AutoCloseable {

    private static ThreadLocal<YourContext> instance = new ThreadLocal<>();

    private HttpServletRequest request;
    private HttpServletResponse response;

    private YourContext(HttpServletRequest request, HttpServletResponse response) {
        this.request = request;
        this.response = response;
    }

    public static YourContext create(HttpServletRequest request, HttpServletResponse response) {
        YourContext context = new YourContext(request, response);
        instance.set(context);
        return context;
    }

    public static YourContext getCurrentInstance() {
        return instance.get();
    }

    @Override    
    public void close() {
        instance.remove();
    }

    public HttpServletRequest getRequest() {
        return request;
    }

    public HttpSession getSession() {
        return request.getSession();
    }

    public ServletContext getServletContext() {
        return request.getServletContext();
    }

    // ... (add if necessary more methods here which return/delegate the request/response).    
}

实施 javax.servlet.Filter 在<$中执行以下操作c $ c> doFilter（）方法并映射到感兴趣的 url-pattern ，例如 / * 或前控制器servlet的 servlet-name 。

Implement javax.servlet.Filter which does the following in doFilter() method and is mapped on an url-pattern of interest, e.g. /* or on the servlet-name of your front controller servlet.

@Override
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws ServletException, IOException {
    HttpServletRequest request = (HttpServletRequest) req;
    HttpServletResponse response = (HttpServletResponse) res;

    try (YourContext context = YourContext.create(request, response)) {
        chain.doFilter(request, response);
    }
}

请注意try-with-resources语句的重要性。它保证在过滤器完成其工作后将调用 YourContext #close（）并且 ThreadLocal 资源将被清除。否则，线程在为另一个HTTP请求回收时仍会包含它。

Note the importance of try-with-resources statement. It guarantees that the YourContext#close() will be called after the filter has done its job and the ThreadLocal resource will be cleared. Otherwise the thread will still contain it when recycled for another HTTP request.

以下是如何在POJO中使用它：

And here's how you could use it in the POJO:

YourContext context = YourContext.getCurrentInstance();
HttpSession session = context.getSession();

这一切基本上也是如何上下文平均MVC框架的对象，如JSF的 FacesContext 和Wicket中的那个。

This all is basically also how the Context objects of the average MVC framework works, like JSF's FacesContext and the one in Wicket.

说，你看过 CDI ？也许更容易制作CDI管理的工件，这样你就可以只相互 @Inject 。

Said that, have you looked at CDI? Perhaps it's easier to make the artifacts CDI-managed so you can just @Inject them in each other.

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