[Java] Improve error messages when parsing a non-SBE schema XML file.

Author: mjpt777

sbe-tool/src/main/java/uk/co/real_logic/sbe/xml/XmlSchemaParser.java

@@ -61,7 +61,7 @@ public class XmlSchemaParser
         "/*[local-name() = 'messageSchema']";
 
     static final String MESSAGE_XPATH_EXPR =
-        "//*[local-name() = 'message']";
+        "/*[local-name() = 'messageSchema']/*[local-name() = 'message']";
 
     /**
      * Validate the document against a given schema. Errors will be written to {@link java.lang.System#err}.
@@ -141,6 +141,11 @@ public static MessageSchema parse(final InputSource is, final ParserOptions opti
         errorHandler.checkIfShouldExit();
 
         final Node schemaNode = (Node)xPath.compile(MESSAGE_SCHEMA_XPATH_EXPR).evaluate(document, XPathConstants.NODE);
+        if (null == schemaNode)
+        {
+            throw new IllegalStateException("messageSchema element not found in document, schema is not valid for SBE");
+        }
+
         final MessageSchema messageSchema = new MessageSchema(schemaNode, typeByNameMap, messageByIdMap);
         errorHandler.checkIfShouldExit();
 
@@ -167,9 +172,9 @@ public static MessageSchema parse(final InputStream in, final ParserOptions opti
     /**
      * Scan XML for all types (encodedDataType, compositeType, enumType, and setType) and save in map.
      *
-     * @param document for the XML parsing
-     * @param xPath    for XPath expression reuse
-     * @return {@link java.util.Map} of name {@link java.lang.String} to Type
+     * @param document for the XML parsing.
+     * @param xPath    for XPath expression reuse.
+     * @return {@link java.util.Map} of name {@link java.lang.String} to {@link Type}.
      * @throws Exception on parsing error.
      */
     public static Map<String, Type> findTypes(final Document document, final XPath xPath) throws Exception
@@ -206,10 +211,10 @@ public static Map<String, Type> findTypes(final Document document, final XPath x
     /**
      * Scan XML for all message definitions and save in map.
      *
-     * @param document      for the XML parsing
-     * @param xPath         for XPath expression reuse
-     * @param typeByNameMap to use for Type objects
-     * @return {@link java.util.Map} of schemaId to Message
+     * @param document      for the XML parsing.
+     * @param xPath         for XPath expression reuse.
+     * @param typeByNameMap to use for Type objects.
+     * @return {@link java.util.Map} of schemaId to {@link Message}.
      * @throws Exception on parsing error.
      */
     public static Map<Long, Message> findMessages(
@@ -221,6 +226,11 @@ public static Map<Long, Message> findMessages(
         forEach((NodeList)xPath.compile(MESSAGE_XPATH_EXPR).evaluate(document, XPathConstants.NODESET),
             (node) -> addMessageWithIdCheck(distinctNames, messageByIdMap, new Message(node, typeByNameMap), node));
 
+        if (messageByIdMap.isEmpty())
+        {
+            handleWarning(document.getDocumentElement(), "no messages found in document");
+        }
+
         return messageByIdMap;
     }
 
@@ -233,8 +243,7 @@ public static Map<Long, Message> findMessages(
     public static void handleError(final Node node, final String msg)
     {
         final ErrorHandler handler = (ErrorHandler)node.getOwnerDocument().getUserData(ERROR_HANDLER_KEY);
-
-        if (handler == null)
+        if (null == handler)
         {
             throw new IllegalStateException("ERROR: " + formatLocationInfo(node) + msg);
         }
@@ -253,8 +262,7 @@ public static void handleError(final Node node, final String msg)
     public static void handleWarning(final Node node, final String msg)
     {
         final ErrorHandler handler = (ErrorHandler)node.getOwnerDocument().getUserData(ERROR_HANDLER_KEY);
-
-        if (handler == null)
+        if (null == handler)
         {
             throw new IllegalStateException("WARNING: " + formatLocationInfo(node) + msg);
         }
@@ -267,13 +275,19 @@ public static void handleWarning(final Node node, final String msg)
     /**
      * Helper function that throws an exception when the attribute is not set.
      *
-     * @param elementNode that should have the attribute
-     * @param attrName    that is to be looked up
-     * @return value of the attribute
-     * @throws IllegalArgumentException if the attribute is not present
+     * @param elementNode that should have the attribute.
+     * @param attrName    that is to be looked up.
+     * @return value of the attribute.
+     * @throws IllegalStateException if the attribute is not present.
      */
     public static String getAttributeValue(final Node elementNode, final String attrName)
     {
+        if (null == elementNode)
+        {
+            throw new IllegalStateException(
+                "element node is null when looking for attribute: " + attrName);
+        }
+
         final NamedNodeMap attributes = elementNode.getAttributes();
         if (null == attributes)
         {
@@ -282,7 +296,7 @@ public static String getAttributeValue(final Node elementNode, final String attr
         }
 
         final Node attrNode = attributes.getNamedItemNS(null, attrName);
-        if (attrNode == null || "".equals(attrNode.getNodeValue()))
+        if (null == attrNode || "".equals(attrNode.getNodeValue()))
         {
             throw new IllegalStateException(
                 "element '" + elementNode.getNodeName() + "' has empty or missing attribute: " + attrName);
@@ -294,22 +308,27 @@ public static String getAttributeValue(final Node elementNode, final String attr
     /**
      * Helper function that uses a default value when value not set.
      *
-     * @param elementNode that should have the attribute
-     * @param attrName    that is to be looked up
-     * @param defValue    String to return if not set
-     * @return value of the attribute or defValue
+     * @param elementNode that should have the attribute.
+     * @param attrName    that is to be looked up.
+     * @param defValue    value to return if not set.
+     * @return value of the attribute or defValue.
      */
     public static String getAttributeValue(final Node elementNode, final String attrName, final String defValue)
     {
+        if (null == elementNode)
+        {
+            throw new IllegalStateException(
+                "element node is null when looking for attribute: " + attrName);
+        }
+
         final NamedNodeMap attributes = elementNode.getAttributes();
-        if (attributes == null)
+        if (null == attributes)
         {
             return defValue;
         }
 
         final Node attrNode = attributes.getNamedItemNS(null, attrName);
-
-        if (attrNode == null)
+        if (null == attrNode)
         {
             return defValue;
         }
@@ -320,9 +339,9 @@ public static String getAttributeValue(final Node elementNode, final String attr
     /**
      * Helper function that hides the null return from {@link org.w3c.dom.NamedNodeMap#getNamedItem(String)}.
      *
-     * @param elementNode that could be null
-     * @param attrName    that is to be looked up
-     * @return null or value of the attribute
+     * @param elementNode that could be null.
+     * @param attrName    that is to be looked up.
+     * @return null or value of the attribute.
      */
     public static String getAttributeValueOrNull(final Node elementNode, final String attrName)
     {
@@ -343,8 +362,8 @@ public static String getAttributeValueOrNull(final Node elementNode, final Strin
     /**
      * Helper function to convert a schema byteOrderName into a {@link ByteOrder}.
      *
-     * @param byteOrderName specified as a FIX SBE string
-     * @return ByteOrder representation
+     * @param byteOrderName specified as a FIX SBE string.
+     * @return ByteOrder representation.
      */
     public static ByteOrder getByteOrder(final String byteOrderName)
     {