Fix #12578 pretty print getParameterMap

jetty-core/jetty-util/src/main/java/org/eclipse/jetty/util/Fields.java

@@ -14,6 +14,7 @@
 package org.eclipse.jetty.util;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
@@ -329,7 +330,31 @@ public Iterator<Field> iterator()
      */
     public Map<String, String[]> toStringArrayMap()
     {
-        Map<String, String[]> result = new LinkedHashMap<>();
+        Map<String, String[]> result = new LinkedHashMap<>()
+        {
+            @Override
+            public String toString()
+            {
+                if (fields.isEmpty())
+                    return "{}";
+
+                StringBuilder sb = new StringBuilder();
+                sb.append('{');
+                for (Iterator<Map.Entry<String, String[]>> i = entrySet().iterator(); i.hasNext();)
+                {
+                    Map.Entry<String, String[]> e = i.next();
+                    String key = e.getKey();
+                    String[] value = e.getValue();
+                    sb.append(key);
+                    sb.append('=');
+                    sb.append(Arrays.asList(value));
+                    if (i.hasNext())
+                        sb.append(',');
+                }
+                sb.append('}');
+                return sb.toString();
+            }
+        };
         fields.forEach((k, f) -> result.put(f.getName(), f.getValues().toArray(new String[0])));
         return result;
     }

jetty-ee10/jetty-ee10-servlet/src/test/java/org/eclipse/jetty/ee10/servlet/RequestTest.java

@@ -16,6 +16,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.io.PrintWriter;
 import java.io.UnsupportedEncodingException;
 import java.net.InetAddress;
 import java.net.Socket;
@@ -626,4 +627,49 @@ protected void service(HttpServletRequest request, HttpServletResponse resp) thr
             assertThat(date, containsString(":"));
         }
     }
+
+    @Test
+    public void testParameters() throws Exception
+    {
+        final AtomicReference<String> parameterMap = new AtomicReference<>();
+
+        startServer(new HttpServlet()
+        {
+            @Override
+            protected void service(HttpServletRequest request, HttpServletResponse resp) throws IOException
+            {
+                parameterMap.set(request.getParameterMap().toString());
+                PrintWriter out = resp.getWriter();
+                out.println(request.getParameter("a"));
+                out.println(request.getParameterValues("a")[1]);
+                out.println(request.getParameterValues("a")[2]);
+                out.println(Arrays.asList(request.getParameterValues("b")));
+                out.println(Arrays.asList(request.getParameterValues("c")));
+                out.println(Arrays.asList(request.getParameterValues("d")));
+
+            }
+        });
+
+        String rawResponse = _connector.getResponse(
+            """
+                POST /test/parameters?a=1&a=2&b=one&c= HTTP/1.1\r
+                Host: localhost\r
+                Connection: close\r
+                Content-Type: application/x-www-form-urlencoded\r
+                Content-Length: 23\r
+                \r
+                a=3&b=two&b=three&d=xyz\r
+                """);
+        HttpTester.Response response = HttpTester.parseResponse(rawResponse);
+        assertThat(response.getStatus(), is(HttpStatus.OK_200));
+        assertThat(parameterMap.get(), is("{a=[1, 2, 3],b=[one, two, three],c=[],d=[xyz]}"));
+        assertThat(response.getContent().replaceAll("\r\n", "\n"), is("""
+            1
+            2
+            3
+            [one, two, three]
+            []
+            [xyz]
+            """));
+    }
 }