[webnfc] Implement push method for Android nfc mojo service.

device/nfc/android/java/src/org/chromium/device/nfc/NfcTagHandler.java

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.device.nfc;
+
+import android.nfc.FormatException;
+import android.nfc.NdefMessage;
+import android.nfc.Tag;
+import android.nfc.TagLostException;
+import android.nfc.tech.Ndef;
+import android.nfc.tech.NdefFormatable;
+import android.nfc.tech.TagTechnology;
+
+import java.io.IOException;
+
+/**
+ * Utility class that provides I/O operations for NFC tags.
+ */
+public final class NfcTagHandler {
+    private final TagTechnology mTech;
+    private final TagTechnologyHandler mTechHandler;
+    private boolean mWasConnected;
+
+    /**
+     * Factory method that creates NfcTagHandler for a given NFC Tag.
+     *
+     * @param tag @see android.nfc.Tag
+     * @return NfcTagHandler or null when unsupported Tag is provided.
+     */
+    public static NfcTagHandler create(Tag tag) {
+        if (tag == null) return null;
+
+        Ndef ndef = Ndef.get(tag);
+        if (ndef != null) return new NfcTagHandler(ndef, new NdefHandler(ndef));
+
+        NdefFormatable formattable = NdefFormatable.get(tag);
+        if (formattable != null) {
+            return new NfcTagHandler(formattable, new NdefFormattableHandler(formattable));
+        }
+
+        return null;
+    }
+
+    /**
+     * NdefFormatable and Ndef interfaces have different signatures for operating with NFC tags.
+     * This interface provides generic methods.
+     */
+    private interface TagTechnologyHandler {
+        public void write(NdefMessage message)
+                throws IOException, TagLostException, FormatException;
+        // TODO(crbug.com/625589): add read method for nfc.watch.
+    }
+
+    /**
+     * Implementation of TagTechnologyHandler that uses Ndef tag technology.
+     * @see android.nfc.tech.Ndef
+     */
+    private static class NdefHandler implements TagTechnologyHandler {
+        private final Ndef mNdef;
+
+        NdefHandler(Ndef ndef) {
+            mNdef = ndef;
+        }
+
+        public void write(NdefMessage message)
+                throws IOException, TagLostException, FormatException {
+            mNdef.writeNdefMessage(message);
+        }
+    }
+
+    /**
+     * Implementation of TagTechnologyHandler that uses NdefFormatable tag technology.
+     * @see android.nfc.tech.NdefFormatable
+     */
+    private static class NdefFormattableHandler implements TagTechnologyHandler {
+        private final NdefFormatable mNdefFormattable;
+
+        NdefFormattableHandler(NdefFormatable ndefFormattable) {
+            mNdefFormattable = ndefFormattable;
+        }
+
+        public void write(NdefMessage message)
+                throws IOException, TagLostException, FormatException {
+            mNdefFormattable.format(message);
+        }
+    }
+
+    private NfcTagHandler(TagTechnology tech, TagTechnologyHandler handler) {
+        mTech = tech;
+        mTechHandler = handler;
+    }
+
+    /**
+     * Connects to NFC tag.
+     */
+    public void connect() throws IOException, TagLostException {
+        if (!mTech.isConnected()) {
+            mTech.connect();
+            mWasConnected = true;
+        }
+    }
+
+    /**
+     * Closes connection.
+     */
+    public void close() throws IOException {
+        mTech.close();
+    }
+
+    /**
+     * Writes NdefMessage to NFC tag.
+     */
+    public void write(NdefMessage message) throws IOException, TagLostException, FormatException {
+        mTechHandler.write(message);
+    }
+
+    /**
+     * If tag was previously connected and subsequent connection to the same tag fails, consider
+     * tag to be out of ragne.

[dcheng, 2016/08/16 20:50:08]

Nit: range

+     */
+    public boolean isTagOutOfRange() {
+        try {
+            connect();
+        } catch (IOException e) {
+            return mWasConnected;
+        }
+        return false;
+    }
+}