add convenient StringUtil isEmpty method (#3687)

* add StringUtil.isEmpty

Signed-off-by: olivier lamy <oliver.lamy@gmail.com>

jetty-client/src/test/java/org/eclipse/jetty/client/HttpClientTLSTest.java

@@ -45,6 +45,7 @@ import org.eclipse.jetty.io.ssl.SslHandshakeListener;
 import org.eclipse.jetty.server.Handler;
 import org.eclipse.jetty.server.Server;
 import org.eclipse.jetty.server.ServerConnector;
+import org.eclipse.jetty.util.StringUtil;
 import org.eclipse.jetty.util.ssl.SslContextFactory;
 import org.eclipse.jetty.util.thread.ExecutorThreadPool;
 import org.eclipse.jetty.util.thread.QueuedThreadPool;
@@ -501,7 +502,7 @@ public class HttpClientTLSTest
                 while (true)
                 {
                     String line = reader.readLine();
-                    if (line == null || line.isEmpty())
+                    if (StringUtil.isEmpty(line))
                         break;
                 }
 

jetty-client/src/test/java/org/eclipse/jetty/client/HttpClientURITest.java

@@ -44,6 +44,7 @@ import org.eclipse.jetty.http.HttpStatus;
 import org.eclipse.jetty.server.handler.AbstractHandler;
 import org.eclipse.jetty.toolchain.test.Net;
 import org.eclipse.jetty.util.Fields;
+import org.eclipse.jetty.util.StringUtil;
 import org.eclipse.jetty.util.URIUtil;
 import org.junit.jupiter.api.Assumptions;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -609,7 +610,7 @@ public class HttpClientURITest extends AbstractHttpClientServerTest
                         while (true)
                         {
                             String line = reader.readLine();
-                            if (line == null || line.isEmpty())
+                            if (StringUtil.isEmpty(line))
                                 break;
                         }
 

jetty-fcgi/fcgi-server/src/main/java/org/eclipse/jetty/fcgi/server/HttpChannelOverFCGI.java

@@ -35,6 +35,7 @@ import org.eclipse.jetty.server.Connector;
 import org.eclipse.jetty.server.HttpChannel;
 import org.eclipse.jetty.server.HttpConfiguration;
 import org.eclipse.jetty.server.HttpTransport;
+import org.eclipse.jetty.util.StringUtil;
 import org.eclipse.jetty.util.log.Log;
 import org.eclipse.jetty.util.log.Logger;
 
@@ -87,7 +88,7 @@ public class HttpChannelOverFCGI extends HttpChannel
     public void onRequest()
     {
         String uri = path;
-        if (query != null && !query.isEmpty())
+        if (!StringUtil.isEmpty(query))
             uri += "?" + query;
         // TODO https?
         onRequest(new MetaData.Request(method, HttpScheme.HTTP.asString(), hostPort, uri, HttpVersion.fromString(version), fields,Long.MIN_VALUE));

jetty-http/src/main/java/org/eclipse/jetty/http/HttpParser.java

@@ -28,6 +28,7 @@ import org.eclipse.jetty.http.HttpTokens.EndOfContent;
 import org.eclipse.jetty.util.ArrayTernaryTrie;
 import org.eclipse.jetty.util.ArrayTrie;
 import org.eclipse.jetty.util.BufferUtil;
+import org.eclipse.jetty.util.StringUtil;
 import org.eclipse.jetty.util.Trie;
 import org.eclipse.jetty.util.Utf8StringBuilder;
 import org.eclipse.jetty.util.log.Log;
@@ -1132,7 +1133,7 @@ public class HttpParser
                                 throw new BadMessageException(HttpStatus.BAD_REQUEST_400,"Header Folding");
 
                             // header value without name - continuation?
-                            if (_valueString==null || _valueString.isEmpty())
+                            if ( StringUtil.isEmpty(_valueString))
                             {
                                 _string.setLength(0);
                                 _length=0;

jetty-http2/http2-server/src/main/java/org/eclipse/jetty/http2/server/HTTP2ServerConnectionFactory.java

@@ -38,6 +38,7 @@ import org.eclipse.jetty.server.Connector;
 import org.eclipse.jetty.server.HttpConfiguration;
 import org.eclipse.jetty.server.NegotiatingServerConnection.CipherDiscriminator;
 import org.eclipse.jetty.util.Callback;
+import org.eclipse.jetty.util.StringUtil;
 import org.eclipse.jetty.util.annotation.Name;
 import org.eclipse.jetty.util.log.Log;
 import org.eclipse.jetty.util.log.Logger;
@@ -116,7 +117,7 @@ public class HTTP2ServerConnectionFactory extends AbstractHTTP2ServerConnectionF
         public void onClose(Session session, GoAwayFrame frame, Callback callback)
         {
             String reason = frame.tryConvertPayload();
-            if (reason != null && !reason.isEmpty())
+            if (!StringUtil.isEmpty(reason))
                 reason = " (" + reason + ")";
             getConnection().onSessionFailure(new EofException(String.format("Close %s/%s", ErrorCode.toString(frame.getError(), null), reason)), callback);
         }

jetty-jmh/src/main/java/org/eclipse/jetty/util/StringIsEmptyBenchmark.java

@@ -0,0 +1,66 @@
+//
+//  ========================================================================
+//  Copyright (c) 1995-2019 Mort Bay Consulting Pty. Ltd.
+//  ------------------------------------------------------------------------
+//  All rights reserved. This program and the accompanying materials
+//  are made available under the terms of the Eclipse Public License v1.0
+//  and Apache License v2.0 which accompanies this distribution.
+//
+//      The Eclipse Public License is available at
+//      http://www.eclipse.org/legal/epl-v10.html
+//
+//      The Apache License v2.0 is available at
+//      http://www.opensource.org/licenses/apache2.0.php
+//
+//  You may elect to redistribute this code under either of these licenses.
+//  ========================================================================
+//
+
+package org.eclipse.jetty.util;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.concurrent.TimeUnit;
+
+@State( Scope.Benchmark)
+@Threads(4)
+@Warmup(iterations = 7, time = 500, timeUnit = TimeUnit.MILLISECONDS)
+@Measurement(iterations = 9, time = 800, timeUnit = TimeUnit.MILLISECONDS)
+public class StringIsEmptyBenchmark
+{
+
+    private static final String SHORT = "beer.com/foo";
+
+    private static final String MEDIUM = "beer.com/foobarbeeerbe/bebbebbebebbe/bebbeghdegde/foobarbeeerbe/bebbebbebebbe/bebbeghdegde";
+
+    private static final String LONG = "beer.com/foobarbeeerbe/bebbebbebebbe/bebbeghdegde/foobarbeeerbe/bebbebbebebbe/bebbeghdegde/foobarbeeerbe/bebbebbebebbe/bebbeghdegde/foobarbeeerbe/bebbebbebebbe/bebbeghdegde/foobarbeeerbe/bebbebbebebbe/bebbeghdegde/foobarbeeerbe/bebbebbebebbe/bebbeghdegde/foobarbeeerbe/bebbebbebebbe/bebbeghdegde";
+
+
+    @Benchmark
+    @BenchmarkMode( Mode.Throughput)
+    public void shortIsEmpty()
+    {
+        StringUtil.isEmpty(SHORT);
+    }
+
+    @Benchmark
+    @BenchmarkMode( Mode.Throughput)
+    public void mediumIsEmpty()
+    {
+        StringUtil.isEmpty(MEDIUM);
+    }
+
+    @Benchmark
+    @BenchmarkMode( Mode.Throughput)
+    public void longIsEmpty()
+    {
+        StringUtil.isEmpty(LONG);
+    }
+}

jetty-server/src/main/java/org/eclipse/jetty/server/session/SessionHandler.java

@@ -725,7 +725,7 @@ public class SessionHandler extends ScopedHandler
         if (isUsingCookies())
         {
             String sessionPath = (_cookieConfig.getPath()==null) ? contextPath : _cookieConfig.getPath();
-            sessionPath = (sessionPath==null||sessionPath.isEmpty()) ? "/" : sessionPath;
+            sessionPath = (StringUtil.isEmpty(sessionPath)) ? "/" : sessionPath;
             String id = getExtendedId(session);
             HttpCookie cookie = null;
             if (_sessionComment == null)

jetty-util/src/main/java/org/eclipse/jetty/util/StringUtil.java

@@ -471,6 +471,29 @@ public class StringUtil
         return true;
     }
 
+    /**
+     * <p>Checks if a String is empty ("") or null.</p>
+     *
+     * <pre>
+     *   isEmpty(null)   == true
+     *   isEmpty("")     == true
+     *   isEmpty("\r\n") == false
+     *   isEmpty("\t")   == false
+     *   isEmpty("   ")  == false
+     *   isEmpty("a")    == false
+     *   isEmpty(".")    == false
+     *   isEmpty(";\n")  == false
+     * </pre>
+     *
+     * @param str
+     *            the string to test.
+     * @return true if string is null or empty.
+     */
+    public static boolean isEmpty(String str)
+    {
+        return str == null || str.isEmpty();
+    }
+
     /* ------------------------------------------------------------ */
     /**
      * Test if a string is not null and contains at least 1 non-whitespace characters in it.

jetty-util/src/test/java/org/eclipse/jetty/util/StringUtilTest.java

@@ -262,6 +262,22 @@ public class StringUtilTest
         assertTrue(StringUtil.isNotBlank(";\n"));
     }
 
+    @Test
+    public void testIsEmpty()
+    {
+        assertTrue(StringUtil.isEmpty(null));
+        assertTrue(StringUtil.isEmpty(""));
+        assertFalse(StringUtil.isEmpty("\r\n"));
+        assertFalse(StringUtil.isEmpty("\t"));
+        assertFalse(StringUtil.isEmpty("   "));
+
+        assertFalse(StringUtil.isEmpty("a"));
+        assertFalse(StringUtil.isEmpty("  a"));
+        assertFalse(StringUtil.isEmpty("a  "));
+        assertFalse(StringUtil.isEmpty("."));
+        assertFalse(StringUtil.isEmpty(";\n"));
+    }
+    
     @Test
     public void testSanitizeHTML()
     {