GWT RPC延迟绑定失败

Question

我们正在共同开发一个GWT Web应用程序，该应用程序已经具有对其他模块的有效RPC调用。 我们构建了一个新的RPC模块（基于现有体系结构），该模块可以编译和运行，但是在以下行中抛出运行时异常失败：

this.dashboardService = GWT.create(DashboardService.class);

控制台中的最后一行是“未捕获的异常转义”，然后是堆栈跟踪到上面的GWT.create()行，其前面是控制台错误消息：

延迟的绑定失败，原因是...预期会导致后续失败[ERROR]

在这两行之前，列出了一系列红色错误，从下面开始：

[INFO] [（...）]-模块...已加载

[DEBUG] [（...）]-重新绑定（...）。DashboardService

[DEBUG] [（...）]-调用生成器com.google.gwt.user.rebind.rpc.ServiceInterfaceProxyGenerator

[DEBUG] [（...）]-为远程服务接口'（...）。DashboardService'生成客户端代理

[INFO] [（...）]-检查类型'java.util.Arrays.ArrayList'的类型参数0，因为该类型或其子类型之一暴露为最大维数为1的数组（通过（......）。DashboardChannelSummary）

。 。 。 （没有堆栈跟踪或行号的更多错误）

控制台询问“您是否忘记了继承模块？” 但是根据我的研究，这不是问题。 问题出在GWT延迟绑定过程中，在堆栈跟踪中不可见。 我怀疑上面的粗体字是问题，但是如果没有行号，我将无法理解该错误消息。 这是专有软件包/模块名称替换为（...）的代码：

web.xml中

<servlet>
    <servlet-name>(...) DashboardService
    </servlet-name>
    <servlet-class>(...).server.DashboardServiceImpl
    </servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>(...) DashboardService
    </servlet-name>
    <url-pattern>/(...)/DashboardService</url-pattern>
</servlet-mapping>

DashboardChannelSummary.java

/**
 * This class is an in memory representation of the results of a document search
 */
public class DashboardChannelSummary implements IsSerializable {
    /** Only searches for documents from the past in this amount (the past week) */
    private static final int DEFAULT_DASHBOARD_HISTORY_IN_DAYS = -7;
    /** array of channels */
    private List<Channel> channels;
    /** iterator */
    private Iterator<Channel> iterator;
    /** */
    private final static String IMAGE_PATH = "/images/channels/";
    /** */
    private final static String IMAGE_EXT = ".png";
    /** constant for the channel header name  */
    public final static String BUSINESS_LABEL = "business aviation";
    /** constant for the channel header name  */
    public final static String COMMERCIAL_LABEL = "commercial aviation";
    /** constant for the channel header name  */
    public final static String MRO_LABEL = "mro";
    /** constant for the channel header name  */
    public final static String DEFENSE_LABEL = "defense";
    /** 
     * 
     */
    public enum CHANNEL_NAME {
        BUSINESS   (BUSINESS_LABEL,   DocumentSummary.BA_ID), 
        COMMERCIAL (COMMERCIAL_LABEL, DocumentSummary.CA_ID), 
        MRO        (MRO_LABEL,        DocumentSummary.MRO_ID),
        DEFENSE    (DEFENSE_LABEL,    DocumentSummary.DEFENSE_ID);
        /** */
        public String label;
        /** */
        public int ID;
        /** */
        private CHANNEL_NAME(String label, int ID) {
            this.label = label.toUpperCase();
            this.ID = ID;
        }
    };

    /**
     * 
     */
    public static List<String> channelNames() {
        ArrayList<String> channels = new ArrayList<String>(CHANNEL_NAME.values().length);
        for(int i=0; i<channels.size(); i++) {
            channels.add(CHANNEL_NAME.values()[i].label);
        }
        return channels;
    }

    /**
     * 
     */
    public static int[] channelIDs() {
        int[] IDs = new int[CHANNEL_NAME.values().length];
        for(int i=0; i<IDs.length; i++) {
            IDs[i] = CHANNEL_NAME.values()[i].ID;
        }
        return IDs;
    }

    /**
     * 
     * @return
     */
    public static int channelCount() {
        return CHANNEL_NAME.values().length;
    }

    /**
     * 
     */
    public static Date cutoffDate() {
        Date date = new Date(0);
        CalendarUtil.addDaysToDate(date, DEFAULT_DASHBOARD_HISTORY_IN_DAYS);
        return date;
    }

    /**
     * 
     */
    public class Channel {
        /** the name of this channel */
        private CHANNEL_NAME name;
        /** The list of documents */
        private List<DocumentSummary> docs;
        /** the iterator */
        private Iterator<DocumentSummary> iterator; 

        /**
         * 
         */
        public Channel(List<DocumentSummary> docs, CHANNEL_NAME name) {
            this.docs = docs;
            this.name = name;
            iterator = docs.iterator();
        }

        /**
         * 
         */
        public String getLabel() {
            return name.label;
        }

        /**
         * 
         */
        public List<DocumentSummary> getDocuments() {
            return docs;
        }

        /**
         * 
         */
        public boolean hasDocuments() {
            return iterator.hasNext();
        }

        /**
         * 
         * @return
         */
        public DocumentSummary nextDocument() {
            if(iterator.hasNext()) {
                return iterator.next();
            }
            else {
                return null;
            }
        }

        /**
         * 
         */
        public String nextImageURL() {
            return GWT.getHostPageBaseURL().concat(IMAGE_PATH + String.valueOf(Random.nextInt(channels.size()) - 1) + IMAGE_EXT);
        }
    }

    /**
     * Constructor
     */
    public DashboardChannelSummary() {
        channels = new ArrayList<Channel>(CHANNEL_NAME.values().length);
        iterator = channels.iterator();
    }

    /**
     * Constructor
     */
    public DashboardChannelSummary(List<List<DocumentSummary>> channelList) {
        channels = new ArrayList<Channel>(CHANNEL_NAME.values().length);
        iterator = channels.iterator();
        int count = 0;
        for(List<DocumentSummary> channelData : channelList)
        {
            channels.add(new Channel(channelData, CHANNEL_NAME.values()[count++]));
        }
    }

    /**
     * @return 
     */
    public List<Channel> getChannels() {
        return channels;
    }

    /**
     * @return 
     */
    public Channel getChannel(int channel) {
        return channels.get(channel);
    }

    /**
     * @return 
     */
    public Channel nextChannel() {
        if(iterator.hasNext()) {
            return iterator.next();
        }
        else {
            return null;
        }
    }

    /**
     * @return 
     */
    public List<DocumentSummary> getDocuments(int channel) {
        return this.getChannel(channel).getDocuments();
    }
}

DashboardPresenter.java：

private final DashboardServiceAsync dashboardService;

以及在构造函数中失败的延迟绑定：

this.dashboardService = GWT.create(DashboardService.class);

DashboardServiceAsync.java：

public interface DashboardServiceAsync {

    /**
     * 
     * @param channelIDs
     * @param startDate
     * @param async
     */
    void getChannelSummary(int[] channelIDs, Date startDate, AsyncCallback<DashboardChannelSummary> async);
}

DashboardService.java：

@RemoteServiceRelativePath("DashboardService") public interface DashboardService extends RemoteService {

    /**
     * 
     * @param channelIDs
     * @param startDate
     * @return
     */
    DashboardChannelSummary getChannelSummary(int[] channelIDs, Date startDate); 
}

在服务器上：

DashboardServiceImpl.java：

public class DashboardServiceImpl extends RemoteServiceServlet implements DashboardService {

    /**
     * 
     * @param channelIDs
     * @param startDate
     * @return
     */
    @Override
    public DashboardChannelSummary getChannelSummary(int[] channelIDs, Date startDate) {
        return new DashboardDaoImpl().getChannelSummary(channelIDs, startDate);
    }
}

我们已经根据文档和关于SO的建议对RPC代码进行了两次和三次检查，以确保准确性，例如确保方法签名在所有接口和实现中都是正确的。 有什么明显的错误跳出来吗？ 有没有一种方法可以更详细地调试此错误？

UPDATE

重新设计了DashboardChannelSummary.java，以最大程度提高将数据从服务器传输到客户端的效率，现在所有属性都可以“可序列化”：

/**
 * This class is an in memory representation of the results of a document search.
 */
public class DashboardChannelSummary implements IsSerializable {
    /** Only searches for documents from the past in this amount (the past week) */
    private static final int DEFAULT_DASHBOARD_HISTORY_IN_DAYS = -7;
    /** array of channels */
    private ArrayList<ArrayList<DocumentSummary>> channels;
    /** */
    private int channel = 0;
    /** */
    private int image = 0;
    /** */
    private int index = 0;
    /** */
    private int last = 0;
    /** */
    private final static String IMAGE_PATH = "images/channels/";
    /** */
    private final static String IMAGE_EXT = ".jpg";
    /** constant for the channel header name  */
    public final static String BUSINESS_LABEL = "business";
    /** constant for the channel header name  */
    public final static String COMMERCIAL_LABEL = "commercial";
    /** constant for the channel header name  */
    public final static String MRO_LABEL = "mro";
    /** constant for the channel header name  */
    public final static String DEFENSE_LABEL = "defense";
    /** 
     * 
     */
    public enum CHANNEL_NAME {
        BUSINESS   (BUSINESS_LABEL,   DocumentSummary.BA_ID,      "bus"), 
        COMMERCIAL (COMMERCIAL_LABEL, DocumentSummary.CA_ID,     "_com"), 
        MRO        (MRO_LABEL,        DocumentSummary.MRO_ID,     "mro"),
        DEFENSE    (DEFENSE_LABEL,    DocumentSummary.DEFENSE_ID, "mil");
        /** */
        public String label;
        /** */
        public int ID;
        /** */
        public String prefix;
        /** */
        private CHANNEL_NAME(String label, int ID, String prefix) {
            this.label = label.toUpperCase();
            this.ID = ID;
            this.prefix = prefix;
        }
    };

    /**
     * 
     */
    private String nextRandomImage() {
        while(index == last) {
            index = Random.nextInt(channels.size()) + 1;
        }
        last = index;
        return String.valueOf(index);
    }

    /**
     * 
     */
    public static List<String> channelNames() {
        ArrayList<String> channels = new ArrayList<String>(CHANNEL_NAME.values().length);
        for(int i=0; i<channels.size(); i++) {
            channels.add(CHANNEL_NAME.values()[i].label);
        }
        return channels;
    }

    /**
     * 
     */
    public static int[] channelIDs() {
        int[] IDs = new int[CHANNEL_NAME.values().length];
        for(int i=0; i<IDs.length; i++) {
            IDs[i] = CHANNEL_NAME.values()[i].ID;
        }
        return IDs;
    }

    /**
     * 
     * @return
     */
    public static int channelCount() {
        return CHANNEL_NAME.values().length;
    }

    /**
     * 
     */
    public static Date cutoffDate() {
        Date date = new Date();
        CalendarUtil.addDaysToDate(date, DEFAULT_DASHBOARD_HISTORY_IN_DAYS);
        return date;
    }


    /**
     * Constructor
     */
    public DashboardChannelSummary() {
    }

    /**
     * Constructor
     */
    public DashboardChannelSummary(ArrayList<ArrayList<DocumentSummary>> channels) {
        this.channels = channels;
    }

    /**
     * 
     */
    public String nextImageURL() {
        if(++image > channels.get(channel - 1).size()) {
            image = 0;
        }
        return GWT.getHostPageBaseURL() +
               IMAGE_PATH + 
               CHANNEL_NAME.values()[channel - 1].prefix + 
               nextRandomImage() + 
               IMAGE_EXT;
    }

    /**
     * 
     */
    public ArrayList<DocumentSummary> nextChannel() {
        return channels.get(channel++);
    }

    /**
     * 
     */
    public String toString() {
        return this.getClass().toString() + " current channel : " + channel;
    }
}

Answer 1

罪魁祸首很可能是DashboardChannelSummary 。 可以肯定的是，将getChannelSummary的返回类型更改为“安全”，例如String或Void 。 如果错误仍然存​​在，则说明服务的配置存在问题（尽管我怀疑它会在GWT的编译阶段出现）。 如果该服务有效，那么您可以确定这是因为DashboardChannelSummary无法序列化。

尽管类本身具有无参数构造函数并实现IsSerializable ，但并非所有字段都可序列化。 您应该仔细查看Channel类（也许也是DocumentSummary ，但问题中没有提供代码）和Iterator字段（ ArrayList返回一个Itr实例，该实例似乎不可序列化）。

如果错误仍然存​​在，请尝试简化DashboardChannelSummary直到获得可用的版本，然后以“向上”的方式工作，直到找到导致错误的部分为止。