Package org.apache.derby.iapi.types

Class XML

  • All Implemented Interfaces:
    java.io.Externalizable, java.io.Serializable, java.lang.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.
    See Also:
    Serialized Form

    • Field Detail

      • BASE_MEMORY_USAGE

        private static final int BASE_MEMORY_USAGE

      • xType

        private int xType

      • xmlStringValue

        private SQLChar xmlStringValue

      • xmlReqCheck

        private static java.lang.String xmlReqCheck

      • containsTopLevelAttr

        private boolean containsTopLevelAttr

    • Constructor Detail

      • 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 Detail

      • 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.
        See Also:
        DataValueDescriptor.cloneValue(boolean)

      • 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.
        See Also:
        DataValueDescriptor.typePrecedence()

      • 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
        See Also:
        DataValueDescriptor.getLength()

      • setValueFromResultSet

        public final void setValueFromResultSet​(java.sql.ResultSet resultSet,
                                        int colNumber,
                                        boolean isNullable)
                                 throws java.sql.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:
        java.sql.SQLException - Error accessing the result set
        See Also:
        DataValueDescriptor.setValueFromResultSet(java.sql.ResultSet, int, boolean)

      • 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
        See Also:
        DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)

      • 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.

      • 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.
        See Also:
        Storable.isNull()

      • readExternal

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

      • writeExternal

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

      • 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