Fix formatting dates at several places. Common mistakes:

- DateFormats are not thread safe
- new Date() is used for formatting which does not specify a locale

We now use a Utils.dateTimeFormat() helper for formatting to ISO 8601 (UTC).

core/src/main/java/org/bitcoinj/core/Block.java

@@ -1,5 +1,6 @@
 /**
  * Copyright 2011 Google Inc.
+ * Copyright 2014 Andreas Schildbach
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -588,7 +589,7 @@ public class Block extends Message {
         s.append("   time: [");
         s.append(time);
         s.append("] ");
-        s.append(new Date(time * 1000));
+        s.append(Utils.dateTimeFormat(time * 1000));
         s.append("\n");
         s.append("   difficulty target (nBits): ");
         s.append(difficultyTarget);

core/src/main/java/org/bitcoinj/core/DownloadListener.java

@@ -1,5 +1,6 @@
 /**
  * Copyright 2011 Google Inc.
+ * Copyright 2014 Andreas Schildbach
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,7 +20,6 @@ package org.bitcoinj.core;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.text.DateFormat;
 import java.util.Date;
 import java.util.concurrent.Semaphore;
 
@@ -80,8 +80,8 @@ public class DownloadListener extends AbstractPeerEventListener {
      * @param date the date of the last block downloaded
      */
     protected void progress(double pct, int blocksSoFar, Date date) {
-        log.info(String.format("Chain download %d%% done with %d blocks to go, block date %s", (int) pct,
+        log.info(String.format("Chain download %d%% done with %d blocks to go, block date %s", (int) pct, blocksSoFar,
-                blocksSoFar, DateFormat.getDateTimeInstance().format(date)));
+                Utils.dateTimeFormat(date)));
     }
 
     /**

core/src/main/java/org/bitcoinj/core/Transaction.java

@@ -32,8 +32,6 @@ import org.slf4j.LoggerFactory;
 
 import javax.annotation.Nullable;
 import java.io.*;
-import java.text.ParseException;
-import java.text.SimpleDateFormat;
 import java.util.*;
 
 import static org.bitcoinj.core.Utils.*;
@@ -1263,19 +1261,6 @@ public class Transaction extends ChildMessage implements Serializable {
         return false;
     }
 
-    /**
-     * Parses the string either as a whole number of blocks, or if it contains slashes as a YYYY/MM/DD format date
-     * and returns the lock time in wire format.
-     */
-    public static long parseLockTimeStr(String lockTimeStr) throws ParseException {
-        if (lockTimeStr.indexOf("/") != -1) {
-            SimpleDateFormat format = new SimpleDateFormat("yyyy/MM/dd", Locale.US);
-            Date date = format.parse(lockTimeStr);
-            return date.getTime() / 1000;
-        }
-        return Long.parseLong(lockTimeStr);
-    }
-
     /**
      * Returns either the lock time as a date, if it was specified in seconds, or an estimate based on the time in
      * the current head block if it was specified as a block time.

core/src/main/java/org/bitcoinj/core/Utils.java

@@ -35,6 +35,8 @@ import java.math.BigInteger;
 import java.net.URL;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
 import java.util.*;
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.BlockingQueue;
@@ -444,6 +446,28 @@ public class Utils {
         return currentTimeMillis() / 1000;
     }
 
+    private static final TimeZone UTC = TimeZone.getTimeZone("UTC");
+
+    /**
+     * Formats a given date+time value to an ISO 8601 string.
+     * @param dateTime value to format, as a Date
+     */
+    public static String dateTimeFormat(Date dateTime) {
+        DateFormat iso8601 = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.US);
+        iso8601.setTimeZone(UTC);
+        return iso8601.format(dateTime);
+    }
+
+    /**
+     * Formats a given date+time value to an ISO 8601 string.
+     * @param dateTime value to format, unix time (ms)
+     */
+    public static String dateTimeFormat(long dateTime) {
+        DateFormat iso8601 = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.US);
+        iso8601.setTimeZone(UTC);
+        return iso8601.format(dateTime);
+    }
+
     public static byte[] copyOf(byte[] in, int length) {
         byte[] out = new byte[length];
         System.arraycopy(in, 0, out, 0, Math.min(length, in.length));

core/src/main/java/org/bitcoinj/protocols/channels/PaymentChannelClient.java

@@ -1,5 +1,6 @@
 /*
  * Copyright 2013 Google Inc.
+ * Copyright 2014 Andreas Schildbach
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,7 +30,6 @@ import org.bitcoin.paymentchannel.Protos;
 import org.slf4j.LoggerFactory;
 
 import javax.annotation.Nullable;
-import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.concurrent.locks.ReentrantLock;
 
@@ -66,8 +66,6 @@ public class PaymentChannelClient implements IPaymentChannelClient {
     // The state object used to step through initialization and pay the server
     @GuardedBy("lock") private PaymentChannelClientState state;
 
-    public static final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ");
-
     // The step we are at in initialization, this is partially duplicated in the state object
     private enum InitStep {
         WAITING_FOR_CONNECTION_OPEN,
@@ -180,7 +178,7 @@ public class PaymentChannelClient implements IPaymentChannelClient {
         checkState( expireTime >= 0 && initiate.getMinAcceptedChannelSize() >= 0);
 
         if (! conn.acceptExpireTime(expireTime)) {
-            log.error("Server suggested expire time was out of our allowed bounds: {} ({} s)", dateFormat.format(new Date(expireTime * 1000)), expireTime);
+            log.error("Server suggested expire time was out of our allowed bounds: {} ({} s)", Utils.dateTimeFormat(expireTime * 1000), expireTime);
             errorBuilder.setCode(Protos.Error.ErrorCode.TIME_WINDOW_UNACCEPTABLE);
             return CloseReason.TIME_WINDOW_UNACCEPTABLE;
         }

core/src/main/java/org/bitcoinj/wallet/DeterministicKeyChain.java

@@ -1,5 +1,5 @@
 /**
- * Copyright 2013 The bitcoinj developers.
+ * Copyright 2014 The bitcoinj developers.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -1277,7 +1277,8 @@ public class DeterministicKeyChain implements EncryptableKeyChain {
                                 seed.toHexString())
                 );
             }
-            builder2.append(String.format("Seed birthday: %d  [%s]%n", seed.getCreationTimeSeconds(), new Date(seed.getCreationTimeSeconds() * 1000)));
+            builder2.append(String.format("Seed birthday: %d  [%s]%n", seed.getCreationTimeSeconds(),
+                    Utils.dateTimeFormat(seed.getCreationTimeSeconds() * 1000)));
         }
         final DeterministicKey watchingKey = getWatchingKey();
         // Don't show if it's been imported from a watching wallet already, because it'd result in a weird/

core/src/test/java/org/bitcoinj/core/UtilsTest.java

@@ -1,5 +1,6 @@
 /**
  * Copyright 2011 Thilo Planz
+ * Copyright 2014 Andreas Schildbach
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +18,8 @@
 package org.bitcoinj.core;
 
 import java.math.BigInteger;
+import java.util.Date;
+
 import org.junit.Test;
 
 import static org.junit.Assert.*;
@@ -52,4 +55,10 @@ public class UtilsTest {
         assertEquals(0x05123456L, Utils.encodeCompactBits(new BigInteger("1234560000", 16)));
         assertEquals(0x0600c0deL, Utils.encodeCompactBits(new BigInteger("c0de000000", 16)));
     }
+
+    @Test
+    public void dateTimeFormat() {
+        assertEquals("2014-11-16T10:54:33Z", Utils.dateTimeFormat(1416135273781L));
+        assertEquals("2014-11-16T10:54:33Z", Utils.dateTimeFormat(new Date(1416135273781L)));
+    }
 }

tools/src/main/java/org/bitcoinj/tools/WalletTool.java

@@ -64,8 +64,10 @@ import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.security.SecureRandom;
 import java.text.ParseException;
+import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.List;
+import java.util.Locale;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
@@ -561,7 +563,7 @@ public class WalletTool {
 
             try {
                 if (lockTimeStr != null) {
-                    t.setLockTime(Transaction.parseLockTimeStr(lockTimeStr));
+                    t.setLockTime(parseLockTimeStr(lockTimeStr));
                     // For lock times to take effect, at least one output must have a non-final sequence number.
                     t.getInputs().get(0).setSequenceNumber(0);
                     // And because we modified the transaction after it was completed, we must re-sign the inputs.
@@ -604,6 +606,19 @@ public class WalletTool {
         }
     }
 
+    /**
+     * Parses the string either as a whole number of blocks, or if it contains slashes as a YYYY/MM/DD format date
+     * and returns the lock time in wire format.
+     */
+    private static long parseLockTimeStr(String lockTimeStr) throws ParseException {
+        if (lockTimeStr.indexOf("/") != -1) {
+            SimpleDateFormat format = new SimpleDateFormat("yyyy/MM/dd", Locale.US);
+            Date date = format.parse(lockTimeStr);
+            return date.getTime() / 1000;
+        }
+        return Long.parseLong(lockTimeStr);
+    }
+
     private static void sendPaymentRequest(String location, boolean verifyPki) {
         if (location.startsWith("http") || location.startsWith("bitcoin")) {
             try {