GWT通讯机制初探

//提供getAddresses()服务的接口类
import java.util.List;

import com.google.gwt.user.client.rpc.RemoteService;
import com.google.gwt.user.client.rpc.RemoteServiceRelativePath;

@RemoteServiceRelativePath("address")
public interface AddressService extends RemoteService{
	public List<Address> getAddresses();
}

/*--------------------*/
//代理接口，提供异步调用服务
import java.util.List;
import com.google.gwt.user.client.rpc.AsyncCallback;

public interface AddressServiceAsync {
	public void getAddresses(AsyncCallback<List<Address>> callback);
}

public class AddressServiceImpl extends RemoteServiceServlet implements AddressService{
	
	private static final long serialVersionUID = 7819604306802209305L;

        //实现从数据库查询地理信息的数据集
	@Override
	public List<Address> getAddresses(){
		List<Address> addr_list = new ArrayList<Address>();
		DBConnectionPool pool = new DBConnectionPool("pool01", "com.mysql.jdbc.Driver", "jdbc:mysql://localhost:3306/db?autoReconnect=true&useUnicode=true&characterEncoding=UTF-8",
				"admin", "admin123", 5);
		System.out.println("[INFO] Connection Pool created!");
		ResultSet rs = null;
		String sqlStmt = "SELECT addr_id,state,city,address,zip,description FROM address";
		try {
			Connection conn = pool.getConnection();
			System.out.println("[INFO] Connection to DB established!");
			PreparedStatement ps = conn.prepareStatement(sqlStmt);
			rs = ps.executeQuery();
			if(rs == null){
				System.out.println("[ERROR] Failed to query data from database!");
				return null;	
			}
			System.out.println("[INFO] Execution of query for address list finished!");
			Address addr = null;
			int cnt = 0;
			while(rs.next()){
				addr = new Address();
				++cnt;
				System.out.println("[INFO] No. " + cnt + " of the result records.");
				addr.setId(rs.getLong("addr_id"));
				addr.setState(rs.getString("state") == null ? "N/A" : rs.getString("state"));
				addr.setCity(rs.getString("city"));
				addr.setAddress(rs.getString("address"));
				addr.setZip(rs.getString("zip"));
				addr.setDescription(rs.getString("description") == null ? "N/A" : rs.getString("description") );
				addr_list.add(addr);
			}
		} catch (SQLException e) {
			System.out.println("[ERROR] Failed to get field value from resultSet!");
			e.printStackTrace();
		}
		return addr_list;
	}

        @Override
	public void onBeforeRequestDeserialized(String serializedRequest){
		System.out.println("[INFO] Received Serialized Request Diagram: " + serializedRequest);
        }

        @Override
	public void onAfterResponseSerialized(String serializedResponse) {
		System.out.println("[INFO] Serialized Response Diagram to be sent: " + serializedResponse);
	}
}

 /**
   * Standard HttpServlet method: handle the POST.
   * 
   * This doPost method swallows ALL exceptions, logs them in the
   * ServletContext, and returns a GENERIC_FAILURE_MSG response with status code
   * 500.
   * 
   * @throws ServletException
   * @throws SerializationException
   */
  @Override
  public final void processPost(HttpServletRequest request,
      HttpServletResponse response) throws IOException, ServletException,
      SerializationException {
    // Read the request fully.
    String requestPayload = readContent(request);

    // Let subclasses see the serialized request.
    onBeforeRequestDeserialized(requestPayload);

    // Invoke the core dispatching logic, which returns the serialized
    // result.
    String responsePayload = processCall(requestPayload);

    // Let subclasses see the serialized response.
    onAfterResponseSerialized(responsePayload);

    // Write the response.
    writeResponse(request, response, responsePayload);
  }

  //本方法处理反序列化后的请求数据
  public String processCall(String payload) throws SerializationException {
    try {
      RPCRequest rpcRequest = RPC.decodeRequest(payload, this.getClass(), this);
      onAfterRequestDeserialized(rpcRequest);
      return RPC.invokeAndEncodeResponse(this, rpcRequest.getMethod(),
          rpcRequest.getParameters(), rpcRequest.getSerializationPolicy(),
          rpcRequest.getFlags());
    } catch (IncompatibleRemoteServiceException ex) {
      log(
          "An IncompatibleRemoteServiceException was thrown while processing this call.",
          ex);
      return RPC.encodeResponseForFailure(null, ex);
    }
  }

/*---------------------- RPC.java -------------------------*/
//RPC类中定义的方法invokeAndEncodeResponse，采用反射机制来调用具体的服务方法。
  public static String invokeAndEncodeResponse(Object target,
      Method serviceMethod, Object[] args,
      SerializationPolicy serializationPolicy, int flags)
      throws SerializationException {
    if (serviceMethod == null) {
      throw new NullPointerException("serviceMethod");
    }

    if (serializationPolicy == null) {
      throw new NullPointerException("serializationPolicy");
    }

    String responsePayload;
    try {
      Object result = serviceMethod.invoke(target, args);

      responsePayload = encodeResponseForSuccess(serviceMethod, result,
          serializationPolicy, flags);
    } catch (IllegalAccessException e) {
      SecurityException securityException = new SecurityException(
          formatIllegalAccessErrorMessage(target, serviceMethod));
      securityException.initCause(e);
      throw securityException;
    } catch (IllegalArgumentException e) {
      SecurityException securityException = new SecurityException(
          formatIllegalArgumentErrorMessage(target, serviceMethod, args));
      securityException.initCause(e);
      throw securityException;
    } catch (InvocationTargetException e) {
      // Try to encode the caught exception
      //
      Throwable cause = e.getCause();

      responsePayload = encodeResponseForFailure(serviceMethod, cause,
          serializationPolicy, flags);
    }

    return responsePayload;
  }

//final ArrayList<Address> addressList = new ArrayList<Address>();
//final ListBox addresses = new ListBox();

AddressServiceAsync as = (AddressServiceAsync) GWT
				.create(AddressService.class);
as.getAddresses(new AsyncCallback<List<Address>>() {
	@Override
	public void onSuccess(List<Address> result) {
		Window.alert("[INFO] Succeed to retrieve data from db!");
		Iterator<Address> it = result.iterator();
		Address address = null;
		while(it.hasNext()){
			address = new Address();
			address = it.next();
			System.out.println("[INFO] Address: " + address.getAddress());
			addresses.addItem(address.getAddress());
			addressList.add(address);
		}
		System.out.println("[INFO] Data in addresses ListBox:");
		addresses.setVisibleItemCount(result.size());
		addressGrid.setAddress(addressList.get(0));
		System.out.println("[INFO] [GMap.getAddresse()] Retrieved addresses already be populated into the ListBox!");
	}

	@Override
	public void onFailure(Throwable caught) {
	        String msg = "[ERROR] Failed to retrieve data from database!";
            	Window.alert(msg);
        	System.out.println(msg);
	        GWT.log(msg, caught);
        }
});

if (!plugin) {
    // try searching for a v1 plugin for backwards compatibility
    var found = false;
    for (var i = 0; i < pluginFinders.length; ++i) {
      try {
        plugin = pluginFinders[i]();
        if (plugin != null && plugin.connect($hosted, $moduleName, window)) {
          return;
        }
      } catch (e) {
      }
    }
    loadIframe("http://gwt.google.com/missing-plugin");
  } else {
    if (plugin.connect(url, topWin.__gwt_SessionID, $hosted, $moduleName,
        $hostedHtmlVersion)) {
      window.onUnload = function() {
        try {
          // wrap in try/catch since plugins are not required to supply this
          plugin.disconnect();
        } catch (e) {
        }
      };
    } else {
      if (errFn) {
        errFn(modName);
      } else {
        alert("Plugin failed to connect to hosted mode server at " + $hosted);
        loadIframe("http://code.google.com/p/google-web-toolkit/wiki/TroubleshootingOOPHM");
      }
    }
  }