Class XML

All Implemented Interfaces:
Externalizable, Serializable, Comparable, Formatable, Storable, StreamStorable, TypedFormat, DataValueDescriptor, Orderable, XMLDataValue

public class XML extends DataType implements XMLDataValue, StreamStorable
This type implements the XMLDataValue interface and thus is the type on which all XML related operations are executed. The first and simplest XML store implementation is a UTF-8 based one--all XML data is stored on disk as a UTF-8 string, just like the other Derby string types. In order to make it possible for smarter XML implementations to exist in the future, this class always writes an "XML implementation id" to disk before writing the rest of its data. When reading the data, the impl id is read first and serves as an indicator of how the rest of the data should be read. So long as there's only one implementation (UTF-8) the impl id can be ignored; but when smarter implementations are written, the impl id will be the key to figuring out how an XML value should be read, written, and processed.
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  • Field Details

    • UTF8_IMPL_ID

      protected static final short UTF8_IMPL_ID
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    • BASE_MEMORY_USAGE

      private static final int BASE_MEMORY_USAGE
    • XQ_PASS_BY_REF

      public static final short XQ_PASS_BY_REF
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    • XQ_PASS_BY_VALUE

      public static final short XQ_PASS_BY_VALUE
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    • XQ_RETURN_SEQUENCE

      public static final short XQ_RETURN_SEQUENCE
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    • XQ_RETURN_CONTENT

      public static final short XQ_RETURN_CONTENT
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    • XQ_EMPTY_ON_EMPTY

      public static final short XQ_EMPTY_ON_EMPTY
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    • XQ_NULL_ON_EMPTY

      public static final short XQ_NULL_ON_EMPTY
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    • XML_DOC_ANY

      public static final int XML_DOC_ANY
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    • XML_SEQUENCE

      public static final int XML_SEQUENCE
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    • xType

      private int xType
    • xmlStringValue

      private SQLChar xmlStringValue
    • xmlReqCheck

      private static String xmlReqCheck
    • containsTopLevelAttr

      private boolean containsTopLevelAttr
    • tmpUtil

      private SqlXmlUtil tmpUtil
  • Constructor Details

    • XML

      public XML()
      Default constructor.
    • XML

      private XML(SQLChar val, int xmlType, boolean seqWithAttr, boolean materialize)
      Private constructor used for the cloneValue method. Returns a new instance of XML whose fields are clones of the values received.
      Parameters:
      val - A SQLChar instance to clone and use for this XML value.
      xmlType - Qualified XML type for "val"
      seqWithAttr - Whether or not "val" corresponds to sequence with one or more top-level attribute nodes.
      materialize - whether or not to force materialization of the underlying source data
  • Method Details

    • cloneValue

      public DataValueDescriptor cloneValue(boolean forceMaterialization)
      Description copied from interface: DataValueDescriptor
      Clone this DataValueDescriptor. Results in a new object that has the same value as this but can be modified independently.

      Even though the objects can be modified independently regardless of the value of forceMaterialization, both the clone and the original may be dependent on the store state if forceMaterialization is set to false. An example is if you need to access the value you just read using cloneValue after the current transaction has ended, or after the source result set has been closed.

      Specified by:
      cloneValue in interface DataValueDescriptor
      Parameters:
      forceMaterialization - any streams representing the data value will be materialized if true, the data value will be kept as a stream if possible if false
      Returns:
      A clone of the DataValueDescriptor with the same initial value as this.
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    • getNewNull

      public DataValueDescriptor getNewNull()
      Description copied from interface: DataValueDescriptor
      Get a new null value of the same type as this data value.
      Specified by:
      getNewNull in interface DataValueDescriptor
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    • getTypeName

      public String getTypeName()
      Description copied from interface: DataValueDescriptor
      Get the SQL name of the datatype
      Specified by:
      getTypeName in interface DataValueDescriptor
      Returns:
      The SQL name of the datatype
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    • typePrecedence

      public int typePrecedence()
      Description copied from class: DataType
      Each built-in type in JSQL has a precedence. This precedence determines how to do type promotion when using binary operators. For example, float has a higher precedence than int, so when adding an int to a float, the result type is float. The precedence for some types is arbitrary. For example, it doesn't matter what the precedence of the boolean type is, since it can't be mixed with other types. But the precedence for the number types is critical. The SQL standard requires that exact numeric types be promoted to approximate numeric when one operator uses both. Also, the precedence is arranged so that one will not lose precision when promoting a type.
      Specified by:
      typePrecedence in interface DataValueDescriptor
      Overrides:
      typePrecedence in class DataType
      Returns:
      The precedence of this type.
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    • getString

      public String getString() throws StandardException
      Description copied from interface: DataValueDescriptor
      Gets the value in the data value descriptor as a String. Throws an exception if the data value is not a string.
      Specified by:
      getString in interface DataValueDescriptor
      Returns:
      The data value as a String.
      Throws:
      StandardException - Thrown on error
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    • getLength

      public int getLength() throws StandardException
      Description copied from interface: DataValueDescriptor
      Gets the length of the data value. The meaning of this is implementation-dependent. For string types, it is the number of characters in the string. For numeric types, it is the number of bytes used to store the number. This is the actual length of this value, not the length of the type it was defined as. For example, a VARCHAR value may be shorter than the declared VARCHAR (maximum) length.
      Specified by:
      getLength in interface DataValueDescriptor
      Returns:
      The length of the data value
      Throws:
      StandardException - On error
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    • estimateMemoryUsage

      public int estimateMemoryUsage()
      Description copied from interface: DataValueDescriptor
      Estimate the memory usage in bytes of the data value and the overhead of the class.
      Specified by:
      estimateMemoryUsage in interface DataValueDescriptor
      Returns:
      the estimated memory usage
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    • readExternalFromArray

      public void readExternalFromArray(ArrayInputStream in) throws IOException
      Description copied from class: DataType
      Read the DataValueDescriptor from the stream. The default implementation calls readExternal(), which accesses the ArrayInputStream as a generic stream. If sub-classes can implement it more efficiently by accessing the array, they should override this method.
      Specified by:
      readExternalFromArray in interface DataValueDescriptor
      Overrides:
      readExternalFromArray in class DataType
      Parameters:
      in - The array stream positioned at the beginning of the byte stream to read from.
      Throws:
      IOException - Usual error is if you try to read past limit on the stream.
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    • setFrom

      protected void setFrom(DataValueDescriptor theValue) throws StandardException
      Description copied from class: DataType
      Set the value of this DataValueDescriptor based on the value of the specified DataValueDescriptor.
      Overrides:
      setFrom in class DataType
      Parameters:
      theValue - The DataValueDescriptor that holds the value to which we want to set this DataValueDescriptor's value.
      Throws:
      StandardException
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    • setValueFromResultSet

      public final void setValueFromResultSet(ResultSet resultSet, int colNumber, boolean isNullable) throws SQLException
      Description copied from interface: DataValueDescriptor
      Set the value based on the value for the specified DataValueDescriptor from the specified ResultSet.
      Specified by:
      setValueFromResultSet in interface DataValueDescriptor
      Parameters:
      resultSet - The specified ResultSet.
      colNumber - The 1-based column # into the resultSet.
      isNullable - Whether or not the column is nullable (No need to call wasNull() if not)
      Throws:
      SQLException - Error accessing the result set
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    • compare

      public int compare(DataValueDescriptor other) throws StandardException
      Compare two XML DataValueDescriptors. NOTE: This method should only be used by the database store for the purpose of index positioning--comparisons of XML type are not allowed from the language side of things. That said, all store wants to do is order the NULLs, so we don't actually have to do a full comparison. Just return an order value based on whether or not this XML value and the other XML value are null. As mentioned in the "compare" method of DataValueDescriptor, nulls are considered equal to other nulls and less than all other values. An example of when this method might be used is if the user executed a query like: select i from x_table where x_col is not null
      Specified by:
      compare in interface DataValueDescriptor
      Parameters:
      other - The Orderable to compare this one to.
      Returns:
      <0 - this Orderable is less than other. 0 - this Orderable equals other. >0 - this Orderable is greater than other. The code should not explicitly look for -1, or 1.
      Throws:
      StandardException - Thrown on error
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    • normalize

      public void normalize(DataTypeDescriptor desiredType, DataValueDescriptor source) throws StandardException
      Normalization method - this method will always be called when storing an XML value into an XML column, for example, when inserting/updating. We always force normalization in this case because we need to make sure the qualified type of the value we're trying to store is XML_DOC_ANY--we don't allow anything else.
      Specified by:
      normalize in interface DataValueDescriptor
      Overrides:
      normalize in class DataType
      Parameters:
      desiredType - The type to normalize the source column to
      source - The value to normalize
      Throws:
      StandardException - Thrown if source is not XML_DOC_ANY.
    • getTypeFormatId

      public int getTypeFormatId()
      Description copied from interface: TypedFormat
      Get a universally unique identifier for the type of this object.
      Specified by:
      getTypeFormatId in interface TypedFormat
      Returns:
      The identifier. (A UUID stuffed in an array of 16 bytes).
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    • isNull

      public boolean isNull()
      Description copied from interface: Storable
      Return whether the value is null or not.
      Specified by:
      isNull in interface Storable
      Returns:
      true if the value is null and false otherwise.
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    • restoreToNull

      public void restoreToNull()
      Description copied from interface: Storable
      Restore this object to its (SQL)null value.
      Specified by:
      restoreToNull in interface Storable
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    • readExternal

      public void readExternal(ObjectInput in) throws IOException
      Read an XML value from an input stream.
      Specified by:
      readExternal in interface Externalizable
      Parameters:
      in - The stream from which we're reading.
      Throws:
      IOException
    • writeExternal

      public void writeExternal(ObjectOutput out) throws IOException
      Write an XML value.
      Specified by:
      writeExternal in interface Externalizable
      Parameters:
      out - The stream to which we're writing.
      Throws:
      IOException
    • returnStream

      public InputStream returnStream()
      Description copied from interface: StreamStorable
      Return the on-disk stream state of the object.
      Specified by:
      returnStream in interface StreamStorable
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    • setStream

      public void setStream(InputStream newStream)
      Description copied from interface: StreamStorable
      sets the on-disk stream state for the object.
      Specified by:
      setStream in interface StreamStorable
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    • loadStream

      public void loadStream() throws StandardException
      Description copied from interface: StreamStorable
      Set the value by reading the stream and converting it to an object form.
      Specified by:
      loadStream in interface StreamStorable
      Throws:
      StandardException - on error
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    • XMLParse

      public XMLDataValue XMLParse(StringDataValue stringValue, boolean preserveWS, SqlXmlUtil sqlxUtil) throws StandardException
      Method to parse an XML string and, if it's valid, store the _serialized_ version locally and then return this XMLDataValue.
      Specified by:
      XMLParse in interface XMLDataValue
      Parameters:
      stringValue - The string value to check.
      preserveWS - Whether or not to preserve ignorable whitespace.
      sqlxUtil - Contains SQL/XML objects and util methods that facilitate execution of XML-related operations
      Returns:
      If 'text' constitutes a valid XML document, it has been stored in this XML value and this XML value is returned; otherwise, an exception is thrown.
      Throws:
      StandardException - Thrown on error.
    • XMLSerialize

      public StringDataValue XMLSerialize(StringDataValue result, int targetType, int targetWidth, int targetCollationType) throws StandardException
      The SQL/XML XMLSerialize operator. Serializes this XML value into a string with a user-specified character type, and returns that string via the received StringDataValue (if the received StringDataValue is non-null and of the correct type; else, a new StringDataValue is returned).
      Specified by:
      XMLSerialize in interface XMLDataValue
      Parameters:
      result - The result of a previous call to this method, null if not called yet.
      targetType - The string type to which we want to serialize.
      targetWidth - The width of the target type.
      targetCollationType - The collation type of the target type.
      Returns:
      A serialized (to string) version of this XML object, in the form of a StringDataValue object.
      Throws:
      StandardException - Thrown on error
    • XMLExists

      public BooleanDataValue XMLExists(SqlXmlUtil sqlxUtil) throws StandardException
      The SQL/XML XMLExists operator. Checks to see if evaluation of the query expression contained within the received util object against this XML value returns at least one item. NOTE: For now, the query expression must be XPath only (XQuery not supported) because that's what Xalan supports.
      Specified by:
      XMLExists in interface XMLDataValue
      Parameters:
      sqlxUtil - Contains SQL/XML objects and util methods that facilitate execution of XML-related operations
      Returns:
      True if evaluation of the query expression stored in sqlxUtil returns at least one node for this XML value; unknown if the xml value is NULL; false otherwise.
      Throws:
      StandardException - Thrown on error
    • XMLQuery

      public XMLDataValue XMLQuery(SqlXmlUtil sqlxUtil, XMLDataValue result) throws StandardException
      Evaluate the XML query expression contained within the received util object against this XML value and store the results into the received XMLDataValue "result" param (assuming "result" is non-null; else create a new XMLDataValue).
      Specified by:
      XMLQuery in interface XMLDataValue
      Parameters:
      sqlxUtil - Contains SQL/XML objects and util methods that facilitate execution of XML-related operations
      result - The result of a previous call to this method; null if not called yet.
      Returns:
      An XMLDataValue whose content corresponds to the serialized version of the results from evaluation of the query expression. Note: this XMLDataValue may not be storable into Derby XML columns.
      Throws:
      StandardException - thrown on error
    • setXType

      public void setXType(int xtype)
      Set this XML value's qualified type.
      Specified by:
      setXType in interface XMLDataValue
    • getXType

      public int getXType()
      Retrieve this XML value's qualified type.
      Specified by:
      getXType in interface XMLDataValue
    • markAsHavingTopLevelAttr

      public void markAsHavingTopLevelAttr()
      Take note of the fact this XML value represents an XML sequence that has one or more top-level attribute nodes.
      Specified by:
      markAsHavingTopLevelAttr in interface XMLDataValue
    • hasTopLevelAttr

      public boolean hasTopLevelAttr()
      Return whether or not this XML value represents a sequence that has one or more top-level attribute nodes.
      Specified by:
      hasTopLevelAttr in interface XMLDataValue
    • checkXMLRequirements

      public static void checkXMLRequirements() throws StandardException
      See if the required JAXP and Xalan classes are in the user's classpath. Assumption is that we will always call this method before instantiating an instance of SqlXmlUtil, and thus we will never get a ClassNotFound exception caused by missing JAXP/Xalan classes. Instead, if either is missing we should throw an informative error indicating what the problem is. NOTE: This method only does the checks necessary to allow successful instantiation of the SqlXmlUtil class. Further checks (esp. the presence of a JAXP _implementation_ in addition to the JAXP _interfaces_) are performed in the SqlXmlUtil constructor.
      Throws:
      StandardException - thrown if the required classes cannot be located in the classpath.
    • checkJAXPRequirement

      private static boolean checkJAXPRequirement()
      Check if we have a JAXP implementation installed.
      Returns:
      true if JAXP is installed, or false otherwise
    • checkXPathRequirement

      private static boolean checkXPathRequirement()
      Check if XPath is supported on this platform.
      Returns:
      true if XPath is supported, or false otherwise