Xtext与Ace Web编辑器代码生成请求失败排查求助

基于Xtext Web编辑器的Ace支持，我在前端调用代码生成服务时遭遇404错误，具体情况如下：

前端触发代码 #

参考文档中的「调用服务」逻辑，通过按钮点击触发生成：

var editor = xtext.createEditor();
$("#save-button").click(function() {
    // editor.xtextServices.saveResource();
    editor.xtextServices.generate();
});

后端生成器实现 #

基于默认Greeting语法编写了代码生成器：

// filename: <MyLovaelyDslName>Generator.xtend

class Phase0Generator extends AbstractGenerator {

    override void doGenerate(
        Resource resource,
        IFileSystemAccess2 fsa,
        IGeneratorContext context
    ) {
        fsa.generateFile('greetings.txt', 'People to greet: ' + 
            resource.allContents
                .filter(Greeting)
                .map[name]
                .join(', '))
    }
}

错误表现 #

浏览器发起的10次GET请求全部返回404：

GET http://localhost:8080/xtext-service/generate?resource=67e22793.veri&requiredStateId=-7ffffff4 404 (Not Found)

随后弹出错误提示：

Xtext service 'generate' failed: Xtext service request failed after 10 attempts.
xtext-ace.js:1114 Xtext service 'generate' failed: Not Found

目前语法高亮和自定义验证功能均正常工作。

已做的配置 #

按照文档要求创建了XtextServlet子类，重写doGet方法拦截请求，能正常处理非generate请求，但不知道如何对接generate的处理逻辑：

@WebServlet(name = "XtextServices", urlPatterns = "/xtext-service/*")
public class Phase0Servlet extends XtextServlet {
    public void init() throws ServletException { /* ... */ }
    public void destroy() { /* ... */ }

    @Override
    protected void doGet(
        HttpServletRequest req,
        HttpServletResponse response
    ) throws ServletException, IOException
    {
        var service = getService(req);
        var serviceType = /* ... */.getParameter("serviceType");
        if (serviceType.equals("generate")) { /* ... */ }
        else                                { /* ... */ }
    }
}

问题出在你的Servlet没有正确实现generate请求的处理逻辑，需要对接Xtext的生成器服务，具体步骤如下：

1. 初始化生成器相关服务
   在Servlet的init方法中，通过Xtext的依赖注入容器获取生成器、生成上下文工厂：

   private IGenerator generator;
   private IGeneratorContext.Factory contextFactory;
   
   @Override
   public void init() throws ServletException {
       super.init();
       Injector injector = getInjector(); // 从父类获取Xtext注入器
       generator = injector.getInstance(IGenerator.class);
       contextFactory = injector.getInstance(IGeneratorContext.Factory.class);
   }
   

2. 实现generate请求处理逻辑
   在doGet的generate分支中，加载目标资源、执行生成并返回结果：

   private void handleGenerateRequest(HttpServletRequest req, HttpServletResponse response) throws IOException {
       String resourceId = req.getParameter("resource");
       // 这里需要实现资源加载逻辑，比如从内存缓存中获取编辑器对应的Resource实例
       Resource resource = loadResource(resourceId);
       
       if (resource == null) {
           response.sendError(HttpServletResponse.SC_NOT_FOUND, "资源不存在");
           return;
       }
   
       // 使用内存文件系统访问器捕获生成的文件内容
       MemoryFileSystemAccess fsa = new MemoryFileSystemAccess();
       IGeneratorContext context = contextFactory.createContext();
   
       try {
           generator.doGenerate(resource, fsa, context);
           // 将生成的文件列表转为JSON返回给前端
           response.setContentType("application/json");
           response.setCharacterEncoding("UTF-8");
           new ObjectMapper().writeValue(response.getWriter(), fsa.getFiles());
       } catch (Exception e) {
           response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, "生成失败：" + e.getMessage());
       }
   }
   
   private Resource loadResource(String resourceId) {
       // 替换为你的资源加载逻辑，比如从编辑器的内存缓存中获取
       return YourResourceStore.getResource(resourceId);
   }
   

3. 完整Servlet代码

   @WebServlet(name = "XtextServices", urlPatterns = "/xtext-service/*")
   public class Phase0Servlet extends XtextServlet {
       private IGenerator generator;
       private IGeneratorContext.Factory contextFactory;
   
       @Override
       public void init() throws ServletException {
           super.init();
           Injector injector = getInjector();
           generator = injector.getInstance(IGenerator.class);
           contextFactory = injector.getInstance(IGeneratorContext.Factory.class);
       }
   
       @Override
       protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
           String serviceType = req.getParameter("serviceType");
           if ("generate".equals(serviceType)) {
               handleGenerateRequest(req, response);
           } else {
               super.doGet(req, response);
           }
       }
   
       private void handleGenerateRequest(HttpServletRequest req, HttpServletResponse response) throws IOException {
           String resourceId = req.getParameter("resource");
           Resource resource = loadResource(resourceId);
           
           if (resource == null) {
               response.sendError(HttpServletResponse.SC_NOT_FOUND, "资源不存在");
               return;
           }
   
           MemoryFileSystemAccess fsa = new MemoryFileSystemAccess();
           IGeneratorContext context = contextFactory.createContext();
   
           try {
               generator.doGenerate(resource, fsa, context);
               response.setContentType("application/json");
               response.setCharacterEncoding("UTF-8");
               new ObjectMapper().writeValue(response.getWriter(), fsa.getFiles());
           } catch (Exception e) {
               response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, "生成失败：" + e.getMessage());
           }
       }
   
       private Resource loadResource(String resourceId) {
           // 替换为你的资源加载逻辑，比如从编辑器的内存缓存中获取
           return YourResourceStore.getResource(resourceId);
       }
   }
   

4. 注意事项

   • 确保你的Phase0Generator已被Xtext的依赖注入容器正确注册，否则injector.getInstance(IGenerator.class)会返回null
   • 资源加载逻辑必须和Xtext Web编辑器的资源管理一致，确保能获取到当前编辑器中的最新内容
   • 前端可以通过editor.xtextServices.generate().then(result => { ... })处理返回的生成结果

内容的提问来源于stack exchange，提问作者OrenIshShalom