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Servlet源码分析

Servlet源码分析

作者: zjlearn | 来源:发表于2016-07-19 16:46 被阅读97次

    前面我们已经分析过了启动过程,现在server可以接受client端的request,并进行处理。
    request由servlet进行处理,并返回结果。现在我们看一下,web.xml文件中的REST API是如何和servlet相对应的。

    web.xml

    下面是web.xml文件中关于connector的servlet的配置信息。

    <!-- Connectors servlet -->
      <servlet>
        <servlet-name>v1.ConnectorsServlet</servlet-name>
        <servlet-class>org.apache.sqoop.server.v1.ConnectorServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
      </servlet>
    
      <servlet-mapping>
        <servlet-name>v1.ConnectorsServlet</servlet-name>
        <url-pattern>/v1/connectors/*</url-pattern>
      </servlet-mapping>
    

    从上面的配置信息我们可以看出关于URL中关于/v1/connectors/*的请求信息都被转发给v1.ConnectorsServlet来进行处理,也就是org.apache.sqoop.server.v1.ConnectorServlet类。

    SqoopProtocolServlet类

    org.apache.sqoop.server.v1包中实现的所有servlet都继承了SqoopProtocolServlet类。SqoopProtocolServlet类继承了HttpServlet类。总体的继承关系如下图所示:

    servlet类间关系图.png

    SqoopProtocolServlet继承了HttpServlet类,实现了doGet, doPut, doPost, doDelete四个方法。并实现了handleGetRequest,handlePostRequest,handlePutRequest, handleDeleteRequest四个方法用于子类进行继承。
    默认的方法实现为各自调用do##的实现。
    如下所示:

    @Override
      protected final void doGet(HttpServletRequest req, HttpServletResponse resp)
          throws ServletException, IOException {
        RequestContext rctx = new RequestContext(req, resp);
    
        try {
          JsonBean bean = handleGetRequest(rctx);
          if (bean != null) {
            sendSuccessResponse(rctx, bean);
          }
        } catch (Exception ex) {
          LOG.error("Exception in GET " + rctx.getPath(), ex);
          sendErrorResponse(rctx, ex);
        }
      }
    ====================
    protected JsonBean handleGetRequest(RequestContext ctx) throws Exception {
        super.doGet(ctx.getRequest(), ctx.getResponse());
    
        return null;
      }
    

    ConnectorServlet类

    ConnectorServlet类仅仅将其请求委托给connectorRequestHandler进行处理。主要实现如下:

    @SuppressWarnings("serial")
    public class ConnectorServlet extends SqoopProtocolServlet {
    
      private RequestHandler connectorRequestHandler;
    
      public ConnectorServlet() {
        connectorRequestHandler = new ConnectorRequestHandler();
      }
    
      @Override
      protected JsonBean handleGetRequest(RequestContext ctx) throws Exception {
        return connectorRequestHandler.handleEvent(ctx);
      }
    }
    

    ConnectorRequestHandler类

    ConnectorRequestHandler类实现RequestHandler接口。主要的功能在于对client端发送的request请求进行处理。
    其处理的主要步骤为:

    • 判断是否为GET (connector只支持HTTP GET方法)
    • 判断是根据id/name还是读取所有的信息
    • 将请求进一步的委托给ConnectorManager读取信息
    • 返回结果
      源代码如下:
    public class ConnectorRequestHandler implements RequestHandler {
    
      private static final Logger LOG = Logger.getLogger(ConnectorRequestHandler.class);
    
      private static final String CONNECTORS_PATH = "connectors";
    
      public ConnectorRequestHandler() {
        LOG.info("ConnectorRequestHandler initialized");
      }
    
      @Override
      public JsonBean handleEvent(RequestContext ctx) {
        // connector only support GET requests
        if (ctx.getMethod() != Method.GET) {
          throw new SqoopException(ServerError.SERVER_0002, "Unsupported HTTP method for connector:"
              + ctx.getMethod());
        }
    
        List<MConnector> connectors;
        Map<Long, ResourceBundle> configParamBundles;
        Locale locale = ctx.getAcceptLanguageHeader();
        String cIdentifier = ctx.getLastURLElement();
    
        LOG.info("ConnectorRequestHandler handles cid: " + cIdentifier);
    
        if (ctx.getPath().contains(CONNECTORS_PATH) || cIdentifier.equals("all")) {
          connectors = ConnectorManager.getInstance().getConnectorConfigurables();
          configParamBundles = ConnectorManager.getInstance().getResourceBundles(locale);
          AuditLoggerManager.getInstance().logAuditEvent(ctx.getUserName(),
              ctx.getRequest().getRemoteAddr(), "get", "connectors", "all");
    
          // Authorization check
          connectors = AuthorizationEngine.filterResource(MResource.TYPE.CONNECTOR, connectors);
    
          return new ConnectorsBean(connectors, configParamBundles);
    
        } else {
          // NOTE: we now support using unique name as well as the connector id
          // NOTE: connectorId is a fallback for older sqoop clients if any, since we want to primarily use unique conenctorNames
          long cId = HandlerUtils.getConnectorIdFromIdentifier(cIdentifier);
    
          configParamBundles = new HashMap<Long, ResourceBundle>();
    
          MConnector connector = ConnectorManager.getInstance().getConnectorConfigurable(cId);
          configParamBundles.put(cId, ConnectorManager.getInstance().getResourceBundle(cId, locale));
    
          AuditLoggerManager.getInstance().logAuditEvent(ctx.getUserName(),
              ctx.getRequest().getRemoteAddr(), "get", "connector", String.valueOf(cIdentifier));
    
          // Authorization check
          AuthorizationEngine.readConnector(String.valueOf(connector.getPersistenceId()));
    
          return new ConnectorBean(Arrays.asList(connector), configParamBundles);
        }
      }
    }
    

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