{"id":1012,"date":"2020-08-13T20:28:48","date_gmt":"2020-08-13T20:28:48","guid":{"rendered":"http:\/\/spiderwiz.org\/project\/?page_id=1012"},"modified":"2025-04-09T06:15:59","modified_gmt":"2025-04-09T06:15:59","slug":"lesson-17","status":"publish","type":"page","link":"https:\/\/spiderwiz.org\/project\/tutorial\/lesson-17\/","title":{"rendered":"Lesson 17: Writing an Import Handler Plugin"},"content":{"rendered":"\n

The Import\/Export concept that can be used as a mechanism to\nbridge between Spiderwiz-based and legacy applications was introduced in Lesson 11<\/a>.\nThe exercise we did there assumed that the interface with the foreign system\nwas based on serialized data, which the default ImportHandler<\/a> was capable of processing.<\/p>\n\n\n\n

There are situations in which this assumption cannot be\nheld. The solution in these cases is to extend ImportHandler<\/code>. In this lesson we will show how to do that.<\/p>\n\n\n\n

The test case that will be demonstrated is the example built\nin Baeldung\u2019s\nGuide to the Java API for WebSocket<\/a>. It is a simple chat application\nin which clients use a web browser to communicate with a server over\nWebSockets. They send chat messages and the server distributes them to all\nclients. We are going to bridge it with the chat system that has been escorting\nus throughout this tutorial, so that every message typed in Baeldung\u2019s\napplication (\u201cthe imported system\u201d from now on) shows also on our system and\nvice versa.<\/p>\n\n\n\n

We will achieve our goal by hooking into Baeldung\u2019s code\n(that you can get here<\/a>) and turning it into a Spiderwiz application\nthat traps chat messages and imports them into the Spiderwiz network, as well\nas exports chat messages received over our network to the imported system.\nSince our system requires that chat messages are exchanged inside Chat Rooms\nand the imported system does not have this notion, we will configure a room\nname to it and users of our system will need to join that room in order to\nexchange messages with the imported system.<\/p>\n\n\n\n

Baeldung\u2019s project is called java-websocket<\/code>. We will stay with this project and update it. The\nfirst step is to add the spiderwiz-core<\/code>\ndependency to its POM:<\/p>\n\n\n\n

<dependency>\n    <groupId>org.spiderwiz<\/groupId>\n    <artifactId>spiderwiz-core<\/artifactId>\n    <version>4.0<\/version>\n<\/dependency><\/pre><\/div>\n\n\n\n
Note that spiderwiz-websocket-server<\/code>\nshall not be included because it would conflict with the mechanism already\nprovided by Baeldung.<\/p>\n\n\n\n
We will place all our stuff in a new package – org.spiderwiz.tutorial.lesson17<\/code>. We\nstart as usual with WebsocketBridgeMain<\/code>:<\/p>\n\n\n\n
package org.spiderwiz.tutorial.lesson17;\n\nimport com.baeldung.model.Message;\nimport java.util.List;\nimport org.spiderwiz.core.DataObject;\nimport org.spiderwiz.core.ImportHandler;\nimport org.spiderwiz.core.Main;\nimport org.spiderwiz.tutorial.objectLib.ChatApp;\nimport org.spiderwiz.tutorial.objectLib.ChatMessage;\nimport org.spiderwiz.tutorial.objectLib.ChatRoom;\nimport org.spiderwiz.tutorial.objectLib.Chatter;\n\n\/**\n * Main class for the Websocket Bridge.\n *\/\npublic class WebsocketBridgeMain extends Main{\n    private static final String ROOT_DIRECTORY = "\/tests\/WebsocketBridge";\n    private static final String CONFIG_FILE_NAME = "ws-bridge.conf";\n    private static final String APP_NAME = "Websocket Chat Bridge";\n    private static final String APP_VERSION = "Z17.01";  \/\/ Version Z17.01: First working version\n    \n    private WebsocketImportHandler importHandler = null;\n\n    public WebsocketBridgeMain() {\n        super(ROOT_DIRECTORY, CONFIG_FILE_NAME, APP_NAME, APP_VERSION);\n    }\n\n    \/**\n     * @return the class instance as WebsocketBridgeMain type.\n     *\/\n    public static WebsocketBridgeMain getInstance() {\n        return (WebsocketBridgeMain)Main.getInstance();\n    }\n\n    \/**\n     * @return the produced objects\n     *\/\n    @Override\n    protected String[] getProducedObjects() {\n        return new String[]{\n            ChatRoom.ObjectCode,\n            Chatter.ObjectCode,\n            ChatMessage.ObjectCode\n        };\n    }\n\n    \/**\n     * @return the consumed objects\n     *\/\n    @Override\n    protected String[] getConsumedObjects() {\n        return new String[]{\n            Chatter.ObjectCode,\n            ChatMessage.ObjectCode\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(ChatRoom.class);\n        factoryList.add(ChatApp.class);\n        factoryList.add(ChatterBridge.class);\n        factoryList.add(ChatMessageBridge.class);\n    }\n\n    \/**\n     * @return the custom import handler instead of the default one.\n     *\/\n    @Override\n    protected ImportHandler createImportHandler() {\n        return new WebsocketImportHandler();\n    }\n\n    public synchronized WebsocketImportHandler getImportHandler() {\n        return importHandler;\n    }\n\n    public synchronized void setImportHandler(WebsocketImportHandler importHandler) {\n        this.importHandler = importHandler;\n    }\n \n    \/**\n     * Pass an imported message to the current import handler, if exists.\n     * @param message\n     *\/\n    public void processImportedMessage(Message message) {\n        WebsocketImportHandler handler = getImportHandler();\n        if (handler != null)\n            handler.processMessage(message);\n    }\n}<\/pre><\/div>\n\n\n\n
The produced object types (line 39) are:<\/p>\n\n\n\n