Fix #86

Author: Katsute

src/main/java/com/kttdevelopment/simplehttpserver/SimpleHttpServerImpl.java

@@ -7,6 +7,7 @@
 import java.net.InetSocketAddress;
 import java.util.*;
 import java.util.concurrent.Executor;
+import java.util.function.BiConsumer;
 
 /**
  * Implementation for {@link SimpleHttpServer}. Applications do not use this class.
@@ -147,15 +148,21 @@ public synchronized final HttpContext createContext(final String context, final
 
     @Override
     public synchronized final HttpContext createContext(final String context, final HttpHandler handler, final Authenticator authenticator){
-        if(!ContextUtil.getContext(context,true,false).equals("/") && handler instanceof RootHandler)
+        final String ct = ContextUtil.getContext(context,true,false);
+        if(!ct.equals("/") && handler instanceof RootHandler)
             throw new IllegalArgumentException("RootHandler can only be used at the root '/' context");
 
         final HttpHandler wrapper = exchange -> {
             handle(exchange);
             handler.handle(exchange);
         };
 
-        final HttpContext hc = server.createContext(ContextUtil.getContext(context,true,false),wrapper);
+
+        for(final HttpContext httpContext : contexts.keySet())
+            if(httpContext.getPath().equals(ct))
+                throw new IllegalArgumentException("The context '" + ct + "' is already occupied");
+
+        final HttpContext hc = server.createContext(ct,wrapper);
         contexts.put(hc,handler);
 
         if(authenticator != null)

src/test/java/simplehttpserver/SimpleHttpServerContextTests.java

@@ -3,6 +3,7 @@
 import com.kttdevelopment.simplehttpserver.*;
 import com.kttdevelopment.simplehttpserver.handler.RootHandler;
 import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpServer;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -133,4 +134,14 @@ public final void createSlashedContext() throws IOException{
             Assert.assertEquals("Context [" + root + "] should correct to \"/\"","/",server.createContext(root).getPath());
     }
 
+
+    @Test(expected = IllegalArgumentException.class)
+    public final void createDuplicateContext() throws IOException{
+        final SimpleHttpServer server = SimpleHttpServer.create();
+        final String context = server.getRandomContext();
+
+        server.createContext(context);
+        server.createContext(context,HttpExchange::close);
+    }
+
 }