{"id":898,"date":"2020-07-24T11:21:15","date_gmt":"2020-07-24T11:21:15","guid":{"rendered":"http:\/\/spiderwiz.org\/project\/?page_id=898"},"modified":"2025-04-09T06:15:58","modified_gmt":"2025-04-09T06:15:58","slug":"lesson-8","status":"publish","type":"page","link":"https:\/\/spiderwiz.org\/project\/tutorial\/lesson-8\/","title":{"rendered":"Lesson 8: Streaming Queries and Data Object Archiving"},"content":{"rendered":"\n

In the previous lesson<\/a> you were introduced to Query Objects and saw how to easily post a query to the service mesh and get a reply from one or more applications. This was a single reply in the case of a closed query, and possibly multiple replies from few applications in the case of an open query \u2013 in both cases each application replied with a single reply object.<\/p>\n\n\n\n

Streaming Queries are a bit different because they allow you to post a single query and get back a stream of objects as a response. We will use this mechanism to implement a \u201cshow my message history\u201d feature.<\/p>\n\n\n\n

Obviously to get message history one needs to keep message history. Normally this would be done with some sort of database or storage files, which has a price tag of development time and performance. We will show here how you can do it in three lines of code and no performance penalty with Data Object Archiving<\/em>.<\/p>\n\n\n\n

Again we will throw a new microservice into our service mesh. We call it Archiver<\/code> \u2013 an application that listens to all chat messages circulating in the network, archives them and restores them from the archive on user requests.<\/p>\n\n\n\n

We start with a new class and modifications in the objectLib<\/code> library. For history requests we use ChatHistoryQuery<\/code>:<\/p>\n\n\n\n

package org.spiderwiz.tutorial.objectLib;\n\nimport org.spiderwiz.annotation.WizField;\nimport org.spiderwiz.core.QueryObject;\nimport org.spiderwiz.zutils.ZDate;\n\n\/**\n * A Query Object used for requesting chat message history. Used as a Streaming Query.\n *\/\npublic class ChatHistoryQuery extends QueryObject{\n    \/**\n     * Mandatory public static field for all data objects.\n     *\/\n        public final static String ObjectCode = "HSTRQWR";\n\n        @WizField private String username;          \/\/ the name of the user requesting the history (query field)\n        @WizField private ZDate since;              \/\/ the starting date of the requested history (query field)\n        @WizField private String room;              \/\/ the name of the room the message is sent in (reply field)\n        @WizField private ZDate messageDate;        \/\/ date and time of the message (reply field)\n        @WizField private String message;           \/\/ message content (reply field)\n\n    public String getUsername() {\n        return username;\n    }\n\n    public void setUsername(String username) {\n        this.username = username;\n    }\n\n    public ZDate getSince() {\n        return since;\n    }\n\n    public void setSince(ZDate since) {\n        this.since = since;\n    }\n\n    public String getRoom() {\n        return room;\n    }\n\n    public void setRoom(String room) {\n        this.room = room;\n    }\n\n    public ZDate getMessageDate() {\n        return messageDate;\n    }\n\n    public void setMessageDate(ZDate messageDate) {\n        this.messageDate = messageDate;\n    }\n\n    public String getMessage() {\n        return message;\n    }\n\n    public void setMessage(String message) {\n        this.message = message;\n    }\n}<\/pre><\/div>\n\n\n\n
The query properties are username<\/code> for identifying the inquiring user and since<\/code> for specifying since when history is requested. The other properties \u2013 room<\/code>, messageDate<\/code> and message<\/code> are response properties that contain information about one history item. As we are talking about streaming queries, responses will be generated repeatedly until the query is fully replied.<\/p>\n\n\n\n
The Chatter<\/code> class, known from the previous lessons, has a new boolean stealth<\/code> property. The Archiver<\/code> acts as a chat user, as it needs to trap all chat messages for archiving. However, we do not want other chatters to be notified when it joins or leaves a room as with regular chatters. Setting stealth<\/code> to true<\/code> prevents these notifications as we will see below. Here is the updated Chatter<\/code> class:<\/p>\n\n\n\n
package org.spiderwiz.tutorial.objectLib;\n\nimport org.spiderwiz.annotation.WizField;\nimport org.spiderwiz.core.DataObject;\nimport org.spiderwiz.zutils.ZDate;\n\n\/**\n * A data object that representing a chat user in a specific chat room\n *\/\npublic class Chatter extends DataObject {\n    \/**\n     * Mandatory public static field for all data objects.\n     *\/\n    public final static String ObjectCode = "CHTTR";\n    \n    @WizField private String name;              \/\/ Contains the name of the chatter\n    @WizField private ZDate birthday;           \/\/ Contains the chatter birth date\n    @WizField private boolean stealth = false;  \/\/ True if chatters shall not be notified when this user joins or leave a room\n\n    public String getName() {\n        return name;\n    }\n\n    public void setName(String name) {\n        this.name = name;\n    }\n\n    public ZDate getBirthday() {\n        return birthday;\n    }\n\n    public void setBirthday(ZDate birthday) {\n        this.birthday = birthday;\n    }\n\n    public boolean isStealth() {\n        return stealth;\n    }\n\n    public void setStealth(boolean stealth) {\n        this.stealth = stealth;\n    }\n\n    \/**\n     * @return ChatRoom object code\n     *\/\n    @Override\n    protected String getParentCode() {\n        return ChatRoom.ObjectCode;\n    }\n\n    \/**\n     * @return false because objects of this class are persistent\n     *\/\n    @Override\n    protected boolean isDisposable() {\n        return false;\n    }\n}<\/pre><\/div>\n\n\n\n
Back to the Archiver, let\u2019s see ArchiverMain<\/code>:<\/p>\n\n\n\n
package org.spiderwiz.tutorial.lesson8.archiver;\n\nimport java.util.List;\nimport org.spiderwiz.core.DataObject;\nimport org.spiderwiz.tutorial.objectLib.ChatHistoryQuery;\nimport org.spiderwiz.tutorial.objectLib.ChatMessage;\nimport org.spiderwiz.tutorial.objectLib.ChatRoom;\nimport org.spiderwiz.tutorial.objectLib.Chatter;\nimport org.spiderwiz.tutorial.objectLib.ConsoleMain;\n\n\/**\n * Provides the entry point of the application. Initializes and executes the Spiderwiz framework.\n *\/\npublic class ArchiverMain extends ConsoleMain {\n    private static final String ROOT_DIRECTORY = "";\n    private static final String CONF_FILENAME = "archiver.conf";\n    private static final String APP_NAME = "Chat Archiver";\n    private static final String APP_VERSION = "Z1.01";  \/\/ Version Z1.01: Initial version\n    static final String MY_USERNAME = "_chat_message_archiver";  \/\/ Use this as the "chatter" name when joining a room\n\n    \/**\n     * Class constructor with constant parameters. Call super constructor and create the user map.\n     *\/\n    public ArchiverMain() {\n        super(ROOT_DIRECTORY, CONF_FILENAME, APP_NAME, APP_VERSION);\n    }\n    \n    \/**\n     * @return the class instance as ArchiverMain type.\n     *\/\n    public static ArchiverMain getInstance() {\n        return (ArchiverMain)ConsoleMain.getInstance();\n    }\n\n    \/**\n     * Application entry point. Instantiate the class and initialize the instance.\n     * \n     * @param args the command line arguments. Not used in this application.\n     *\/\n    public static void main(String[] args) {\n        new ArchiverMain().init();\n    }\n\n    \/**\n     * @return the list of produced objects\n     *\/\n    @Override\n    protected String[] getProducedObjects() {\n        return new String[]{\n            Chatter.ObjectCode              \/\/ To notify when we join a room (we will join every room)\n        };\n    }\n\n    \/**\n     * @return the list of consumed objects\n     *\/\n    @Override\n    protected String[] getConsumedObjects() {\n        return new String[]{\n            ChatRoom.ObjectCode,            \/\/ Needs to know about every new room\n            Chatter.ObjectCode,             \/\/ Needs to know the name of every chatter\n            ChatMessage.ObjectCode,         \/\/ Listens to every message for archiving.\n            ChatHistoryQuery.ObjectCode     \/\/ Replier of this query.\n        };\n    }\n\n    \/**\n     * Add implementation classes to the object factory list of this application.\n     * @param factoryList\n     *\/\n    @Override\n    protected void populateObjectFactory(List<Class<? extends DataObject>> factoryList) {\n        super.populateObjectFactory(factoryList);\n        factoryList.add(ChatRoomArchiver.class);\n        factoryList.add(Chatter.class);\n        factoryList.add(ChatMessageArchiver.class);\n        factoryList.add(ChatHistoryQueryReply.class);\n        factoryList.add(ArchivedUser.class);\n        factoryList.add(ArchivedChatItem.class);\n    }\n    \n    \/**\n     * Process an input line - nothing to process in our case.\n     * @param line      The input line\n     * @return true\n     *\/\n    @Override\n    protected boolean processConsoleLine(String line) {\n        return true;\n    }\n}<\/pre><\/div>\n\n\n\n
Archiver<\/code> consumes (line 58) the following object types:<\/p>\n\n\n\n