1 files changed, 76 insertions, 0 deletions
diff --git a/server/src/com/vaadin/terminal/AbstractExtension.java b/server/src/com/vaadin/terminal/AbstractExtension.java
new file mode 100644
index 0000000000..33a60e39ef
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+++ b/server/src/com/vaadin/terminal/AbstractExtension.java
@@ -0,0 +1,76 @@
+/*
+@VaadinApache2LicenseForJavaFiles@
+ */
+
+package com.vaadin.terminal;
+
+import com.vaadin.terminal.gwt.server.ClientConnector;
+
+/**
+ * An extension is an entity that is attached to a Component or another
+ * Extension and independently communicates between client and server.
+ * <p>
+ * Extensions can use shared state and RPC in the same way as components.
+ * <p>
+ * AbstractExtension adds a mechanism for adding the extension to any Connector
+ * (extend). To let the Extension determine what kind target it can be added to,
+ * the extend method is declared as protected.
+ * 
+ * @author Vaadin Ltd
+ * @version @VERSION@
+ * @since 7.0.0
+ */
+public abstract class AbstractExtension extends AbstractClientConnector
+        implements Extension {
+    private boolean previouslyAttached = false;
+
+    /**
+     * Gets a type that the parent must be an instance of. Override this if the
+     * extension only support certain targets, e.g. if only TextFields can be
+     * extended.
+     * 
+     * @return a type that the parent must be an instance of
+     */
+    protected Class<? extends ClientConnector> getSupportedParentType() {
+        return ClientConnector.class;
+    }
+
+    /**
+     * Add this extension to the target connector. This method is protected to
+     * allow subclasses to require a more specific type of target.
+     * 
+     * @param target
+     *            the connector to attach this extension to
+     */
+    protected void extend(AbstractClientConnector target) {
+        target.addExtension(this);
+    }
+
+    /**
+     * Remove this extension from its target. After an extension has been
+     * removed, it can not be attached again.
+     */
+    public void removeFromTarget() {
+        getParent().removeExtension(this);
+    }
+
+    @Override
+    public void setParent(ClientConnector parent) {
+        if (previouslyAttached && parent != null) {
+            throw new IllegalStateException(
+                    "An extension can not be set to extend a new target after getting detached from the previous.");
+        }
+
+        Class<? extends ClientConnector> supportedParentType = getSupportedParentType();
+        if (parent == null || supportedParentType.isInstance(parent)) {
+            super.setParent(parent);
+            previouslyAttached = true;
+        } else {
+            throw new IllegalArgumentException(getClass().getName()
+                    + " can only be attached to targets of type "
+                    + supportedParentType.getName() + " but attach to "
+                    + parent.getClass().getName() + " was attempted.");
+        }
+    }
+
+}