前面我們已經(jīng)分析過(guò)了啟動(dòng)過(guò)程，現(xiàn)在server可以接受client端的request停巷，并進(jìn)行處理。
request由servlet進(jìn)行處理榕栏，并返回結(jié)果∨锨冢現(xiàn)在我們看一下，web.xml文件中的REST API是如何和servlet相對(duì)應(yīng)的扒磁。

web.xml

下面是web.xml文件中關(guān)于connector的servlet的配置信息庆揪。

<!-- 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>

從上面的配置信息我們可以看出關(guān)于URL中關(guān)于/v1/connectors/*的請(qǐng)求信息都被轉(zhuǎn)發(fā)給v1.ConnectorsServlet來(lái)進(jìn)行處理，也就是org.apache.sqoop.server.v1.ConnectorServlet類妨托。

SqoopProtocolServlet類

org.apache.sqoop.server.v1包中實(shí)現(xiàn)的所有servlet都繼承了SqoopProtocolServlet類缸榛。SqoopProtocolServlet類繼承了HttpServlet類±忌耍總體的繼承關(guān)系如下圖所示：

servlet類間關(guān)系圖.png

SqoopProtocolServlet繼承了HttpServlet類内颗，實(shí)現(xiàn)了doGet, doPut, doPost, doDelete四個(gè)方法。并實(shí)現(xiàn)了handleGetRequest敦腔，handlePostRequest均澳，handlePutRequest， handleDeleteRequest四個(gè)方法用于子類進(jìn)行繼承会烙。
默認(rèn)的方法實(shí)現(xiàn)為各自調(diào)用do##的實(shí)現(xiàn)负懦。
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類

ConnectorServlet類僅僅將其請(qǐng)求委托給connectorRequestHandler進(jìn)行處理筒捺。主要實(shí)現(xiàn)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類

ConnectorRequestHandler類實(shí)現(xiàn)RequestHandler接口柏腻。主要的功能在于對(duì)client端發(fā)送的request請(qǐng)求進(jìn)行處理。
其處理的主要步驟為：

• 判斷是否為GET （connector只支持HTTP GET方法）
• 判斷是根據(jù)id/name還是讀取所有的信息
• 將請(qǐng)求進(jìn)一步的委托給ConnectorManager讀取信息
• 返回結(jié)果
  源代碼如下：

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);
    }
  }
}