/*
* Copyright 2002-2013 Drew Noakes
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* More information about this project is available at:
*
* http://drewnoakes.com/code/exif/
* http://code.google.com/p/metadata-extractor/
*/
package com.drew.metadata;
import com.drew.lang.Rational;
import com.drew.lang.annotations.NotNull;
import com.drew.lang.annotations.Nullable;
import com.drew.lang.annotations.SuppressWarnings;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Array;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;
/**
* Abstract base class for all directory implementations, having methods for getting and setting tag values of various
* data types.
*
* @author Drew Noakes http://drewnoakes.com
*/
public abstract class Directory
{
/** Map of values hashed by type identifiers. */
@NotNull
protected final Map<Integer, Object> _tagMap = new HashMap<Integer, Object>();
/**
* A convenient list holding tag values in the order in which they were stored.
* This is used for creation of an iterator, and for counting the number of
* defined tags.
*/
@NotNull
protected final Collection<Tag> _definedTagList = new ArrayList<Tag>();
@NotNull
private final Collection<String> _errorList = new ArrayList<String>(4);
/** The descriptor used to interpret tag values. */
protected TagDescriptor _descriptor;
// ABSTRACT METHODS
/**
* Provides the name of the directory, for display purposes. E.g. <code>Exif</code>
*
* @return the name of the directory
*/
@NotNull
public abstract String getName();
/**
* Provides the map of tag names, hashed by tag type identifier.
*
* @return the map of tag names
*/
@NotNull
protected abstract HashMap<Integer, String> getTagNameMap();
protected Directory()
{}
// VARIOUS METHODS
/**
* Indicates whether the specified tag type has been set.
*
* @param tagType the tag type to check for
* @return true if a value exists for the specified tag type, false if not
*/
@java.lang.SuppressWarnings({ "UnnecessaryBoxing" })
public boolean containsTag(int tagType)
{
return _tagMap.containsKey(Integer.valueOf(tagType));
}
/**
* Returns an Iterator of Tag instances that have been set in this Directory.
*
* @return an Iterator of Tag instances
*/
@NotNull
public Collection<Tag> getTags()
{
return _definedTagList;
}
/**
* Returns the number of tags set in this Directory.
*
* @return the number of tags set in this Directory
*/
public int getTagCount()
{
return _definedTagList.size();
}
/**
* Sets the descriptor used to interpret tag values.
*
* @param descriptor the descriptor used to interpret tag values
*/
@java.lang.SuppressWarnings({ "ConstantConditions" })
public void setDescriptor(@NotNull TagDescriptor descriptor)
{
if (descriptor == null)
throw new NullPointerException("cannot set a null descriptor");
_descriptor = descriptor;
}
/**
* Registers an error message with this directory.
*
* @param message an error message.
*/
public void addError(@NotNull String message)
{
_errorList.add(message);
}
/**
* Gets a value indicating whether this directory has any error messages.
*
* @return true if the directory contains errors, otherwise false
*/
public boolean hasErrors()
{
return _errorList.size() > 0;
}
/**
* Used to iterate over any error messages contained in this directory.
*
* @return an iterable collection of error message strings.
*/
@NotNull
public Iterable<String> getErrors()
{
return _errorList;
}
/** Returns the count of error messages in this directory. */
public int getErrorCount()
{
return _errorList.size();
}
// TAG SETTERS
/**
* Sets an <code>int</code> value for the specified tag.
*
* @param tagType the tag's value as an int
* @param value the value for the specified tag as an int
*/
public void setInt(int tagType, int value)
{
setObject(tagType, value);
}
/**
* Sets an <code>int[]</code> (array) for the specified tag.
*
* @param tagType the tag identifier
* @param ints the int array to store
*/
public void setIntArray(int tagType, @NotNull int[] ints)
{
setObjectArray(tagType, ints);
}
/**
* Sets a <code>float</code> value for the specified tag.
*
* @param tagType the tag's value as an int
* @param value the value for the specified tag as a float
*/
public void setFloat(int tagType, float value)
{
setObject(tagType, value);
}
/**
* Sets a <code>float[]</code> (array) for the specified tag.
*
* @param tagType the tag identifier
* @param floats the float array to store
*/
public void setFloatArray(int tagType, @NotNull float[] floats)
{
setObjectArray(tagType, floats);
}
/**
* Sets a <code>double</code> value for the specified tag.
*
* @param tagType the tag's value as an int
* @param value the value for the specified tag as a double
*/
public void setDouble(int tagType, double value)
{
setObject(tagType, value);
}
/**
* Sets a <code>double[]</code> (array) for the specified tag.
*
* @param tagType the tag identifier
* @param doubles the double array to store
*/
public void setDoubleArray(int tagType, @NotNull double[] doubles)
{
setObjectArray(tagType, doubles);
}
/**
* Sets a <code>String</code> value for the specified tag.
*
* @param tagType the tag's value as an int
* @param value the value for the specified tag as a String
*/
@java.lang.SuppressWarnings({ "ConstantConditions" })
public void setString(int tagType, @NotNull String value)
{
if (value == null)
throw new NullPointerException("cannot set a null String");
setObject(tagType, value);
}
/**
* Sets a <code>String[]</code> (array) for the specified tag.
*
* @param tagType the tag identifier
* @param strings the String array to store
*/
public void setStringArray(int tagType, @NotNull String[] strings)
{
setObjectArray(tagType, strings);
}
/**
* Sets a <code>boolean</code> value for the specified tag.
*
* @param tagType the tag's value as an int
* @param value the value for the specified tag as a boolean
*/
public void setBoolean(int tagType, boolean value)
{
setObject(tagType, value);
}
/**
* Sets a <code>long</code> value for the specified tag.
*
* @param tagType the tag's value as an int
* @param value the value for the specified tag as a long
*/
public void setLong(int tagType, long value)
{
setObject(tagType, value);
}
/**
* Sets a <code>java.util.Date</code> value for the specified tag.
*
* @param tagType the tag's value as an int
* @param value the value for the specified tag as a java.util.Date
*/
public void setDate(int tagType, @NotNull java.util.Date value)
{
setObject(tagType, value);
}
/**
* Sets a <code>Rational</code> value for the specified tag.
*
* @param tagType the tag's value as an int
* @param rational rational number
*/
public void setRational(int tagType, @NotNull Rational rational)
{
setObject(tagType, rational);
}
/**
* Sets a <code>Rational[]</code> (array) for the specified tag.
*
* @param tagType the tag identifier
* @param rationals the Rational array to store
*/
public void setRationalArray(int tagType, @NotNull Rational[] rationals)
{
setObjectArray(tagType, rationals);
}
/**
* Sets a <code>byte[]</code> (array) for the specified tag.
*
* @param tagType the tag identifier
* @param bytes the byte array to store
*/
public void setByteArray(int tagType, @NotNull byte[] bytes)
{
setObjectArray(tagType, bytes);
}
/**
* Sets a <code>Object</code> for the specified tag.
*
* @param tagType the tag's value as an int
* @param value the value for the specified tag
* @throws NullPointerException if value is <code>null</code>
*/
@java.lang.SuppressWarnings( { "ConstantConditions", "UnnecessaryBoxing" })
public void setObject(int tagType, @NotNull Object value)
{
if (value == null)
throw new NullPointerException("cannot set a null object");
if (!_tagMap.containsKey(Integer.valueOf(tagType))) {
_definedTagList.add(new Tag(tagType, this));
}
// else {
// final Object oldValue = _tagMap.get(tagType);
// if (!oldValue.equals(value))
// addError(String.format("Overwritten tag 0x%s (%s). Old=%s, New=%s", Integer.toHexString(tagType), getTagName(tagType), oldValue, value));
// }
_tagMap.put(tagType, value);
}
/**
* Sets an array <code>Object</code> for the specified tag.
*
* @param tagType the tag's value as an int
* @param array the array of values for the specified tag
*/
public void setObjectArray(int tagType, @NotNull Object array)
{
// for now, we don't do anything special -- this method might be a candidate for removal once the dust settles
setObject(tagType, array);
}
// TAG GETTERS
/**
* Returns the specified tag's value as an int, if possible. Every attempt to represent the tag's value as an int
* is taken. Here is a list of the action taken depending upon the tag's original type:
* <ul>
* <li> int - Return unchanged.
* <li> Number - Return an int value (real numbers are truncated).
* <li> Rational - Truncate any fractional part and returns remaining int.
* <li> String - Attempt to parse string as an int. If this fails, convert the char[] to an int (using shifts and OR).
* <li> Rational[] - Return int value of first item in array.
* <li> byte[] - Return int value of first item in array.
* <li> int[] - Return int value of first item in array.
* </ul>
*
* @throws MetadataException if no value exists for tagType or if it cannot be converted to an int.
*/
public int getInt(int tagType) throws MetadataException
{
Integer integer = getInteger(tagType);
if (integer!=null)
return integer;
Object o = getObject(tagType);
if (o == null)
throw new MetadataException("Tag '" + getTagName(tagType) + "' has not been set -- check using containsTag() first");
throw new MetadataException("Tag '" + tagType + "' cannot be converted to int. It is of type '" + o.getClass() + "'.");
}
/**
* Returns the specified tag's value as an Integer, if possible. Every attempt to represent the tag's value as an
* Integer is taken. Here is a list of the action taken depending upon the tag's original type:
* <ul>
* <li> int - Return unchanged
* <li> Number - Return an int value (real numbers are truncated)
* <li> Rational - Truncate any fractional part and returns remaining int
* <li> String - Attempt to parse string as an int. If this fails, convert the char[] to an int (using shifts and OR)
* <li> Rational[] - Return int value of first item in array if length > 0
* <li> byte[] - Return int value of first item in array if length > 0
* <li> int[] - Return int value of first item in array if length > 0
* </ul>
*
* If the value is not found or cannot be converted to int, <code>null</code> is returned.
*/
@Nullable
public Integer getInteger(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof Number) {
return ((Number)o).intValue();
} else if (o instanceof String) {
try {
return Integer.parseInt((String)o);
} catch (NumberFormatException nfe) {
// convert the char array to an int
String s = (String)o;
byte[] bytes = s.getBytes();
long val = 0;
for (byte aByte : bytes) {
val = val << 8;
val += (aByte & 0xff);
}
return (int)val;
}
} else if (o instanceof Rational[]) {
Rational[] rationals = (Rational[])o;
if (rationals.length == 1)
return rationals[0].intValue();
} else if (o instanceof byte[]) {
byte[] bytes = (byte[])o;
if (bytes.length == 1)
return (int)bytes[0];
} else if (o instanceof int[]) {
int[] ints = (int[])o;
if (ints.length == 1)
return ints[0];
}
return null;
}
/**
* Gets the specified tag's value as a String array, if possible. Only supported
* where the tag is set as String[], String, int[], byte[] or Rational[].
*
* @param tagType the tag identifier
* @return the tag's value as an array of Strings. If the value is unset or cannot be converted, <code>null</code> is returned.
*/
@Nullable
public String[] getStringArray(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof String[])
return (String[])o;
if (o instanceof String)
return new String[] { (String)o };
if (o instanceof int[]) {
int[] ints = (int[])o;
String[] strings = new String[ints.length];
for (int i = 0; i < strings.length; i++)
strings[i] = Integer.toString(ints[i]);
return strings;
} else if (o instanceof byte[]) {
byte[] bytes = (byte[])o;
String[] strings = new String[bytes.length];
for (int i = 0; i < strings.length; i++)
strings[i] = Byte.toString(bytes[i]);
return strings;
} else if (o instanceof Rational[]) {
Rational[] rationals = (Rational[])o;
String[] strings = new String[rationals.length];
for (int i = 0; i < strings.length; i++)
strings[i] = rationals[i].toSimpleString(false);
return strings;
}
return null;
}
/**
* Gets the specified tag's value as an int array, if possible. Only supported
* where the tag is set as String, Integer, int[], byte[] or Rational[].
*
* @param tagType the tag identifier
* @return the tag's value as an int array
*/
@Nullable
public int[] getIntArray(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof int[])
return (int[])o;
if (o instanceof Rational[]) {
Rational[] rationals = (Rational[])o;
int[] ints = new int[rationals.length];
for (int i = 0; i < ints.length; i++) {
ints[i] = rationals[i].intValue();
}
return ints;
}
if (o instanceof short[]) {
short[] shorts = (short[])o;
int[] ints = new int[shorts.length];
for (int i = 0; i < shorts.length; i++) {
ints[i] = shorts[i];
}
return ints;
}
if (o instanceof byte[]) {
byte[] bytes = (byte[])o;
int[] ints = new int[bytes.length];
for (int i = 0; i < bytes.length; i++) {
ints[i] = bytes[i];
}
return ints;
}
if (o instanceof CharSequence) {
CharSequence str = (CharSequence)o;
int[] ints = new int[str.length()];
for (int i = 0; i < str.length(); i++) {
ints[i] = str.charAt(i);
}
return ints;
}
if (o instanceof Integer)
return new int[] { (Integer)o };
return null;
}
/**
* Gets the specified tag's value as an byte array, if possible. Only supported
* where the tag is set as String, Integer, int[], byte[] or Rational[].
*
* @param tagType the tag identifier
* @return the tag's value as a byte array
*/
@Nullable
public byte[] getByteArray(int tagType)
{
Object o = getObject(tagType);
if (o == null) {
return null;
} else if (o instanceof Rational[]) {
Rational[] rationals = (Rational[])o;
byte[] bytes = new byte[rationals.length];
for (int i = 0; i < bytes.length; i++) {
bytes[i] = rationals[i].byteValue();
}
return bytes;
} else if (o instanceof byte[]) {
return (byte[])o;
} else if (o instanceof int[]) {
int[] ints = (int[])o;
byte[] bytes = new byte[ints.length];
for (int i = 0; i < ints.length; i++) {
bytes[i] = (byte)ints[i];
}
return bytes;
} else if (o instanceof short[]) {
short[] shorts = (short[])o;
byte[] bytes = new byte[shorts.length];
for (int i = 0; i < shorts.length; i++) {
bytes[i] = (byte)shorts[i];
}
return bytes;
} else if (o instanceof CharSequence) {
CharSequence str = (CharSequence)o;
byte[] bytes = new byte[str.length()];
for (int i = 0; i < str.length(); i++) {
bytes[i] = (byte)str.charAt(i);
}
return bytes;
}
if (o instanceof Integer)
return new byte[] { ((Integer)o).byteValue() };
return null;
}
/** Returns the specified tag's value as a double, if possible. */
public double getDouble(int tagType) throws MetadataException
{
Double value = getDoubleObject(tagType);
if (value!=null)
return value;
Object o = getObject(tagType);
if (o == null)
throw new MetadataException("Tag '" + getTagName(tagType) + "' has not been set -- check using containsTag() first");
throw new MetadataException("Tag '" + tagType + "' cannot be converted to a double. It is of type '" + o.getClass() + "'.");
}
/** Returns the specified tag's value as a Double. If the tag is not set or cannot be converted, <code>null</code> is returned. */
@Nullable
public Double getDoubleObject(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof String) {
try {
return Double.parseDouble((String)o);
} catch (NumberFormatException nfe) {
return null;
}
}
if (o instanceof Number)
return ((Number)o).doubleValue();
return null;
}
/** Returns the specified tag's value as a float, if possible. */
public float getFloat(int tagType) throws MetadataException
{
Float value = getFloatObject(tagType);
if (value!=null)
return value;
Object o = getObject(tagType);
if (o == null)
throw new MetadataException("Tag '" + getTagName(tagType) + "' has not been set -- check using containsTag() first");
throw new MetadataException("Tag '" + tagType + "' cannot be converted to a float. It is of type '" + o.getClass() + "'.");
}
/** Returns the specified tag's value as a float. If the tag is not set or cannot be converted, <code>null</code> is returned. */
@Nullable
public Float getFloatObject(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof String) {
try {
return Float.parseFloat((String)o);
} catch (NumberFormatException nfe) {
return null;
}
}
if (o instanceof Number)
return ((Number)o).floatValue();
return null;
}
/** Returns the specified tag's value as a long, if possible. */
public long getLong(int tagType) throws MetadataException
{
Long value = getLongObject(tagType);
if (value!=null)
return value;
Object o = getObject(tagType);
if (o == null)
throw new MetadataException("Tag '" + getTagName(tagType) + "' has not been set -- check using containsTag() first");
throw new MetadataException("Tag '" + tagType + "' cannot be converted to a long. It is of type '" + o.getClass() + "'.");
}
/** Returns the specified tag's value as a long. If the tag is not set or cannot be converted, <code>null</code> is returned. */
@Nullable
public Long getLongObject(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof String) {
try {
return Long.parseLong((String)o);
} catch (NumberFormatException nfe) {
return null;
}
}
if (o instanceof Number)
return ((Number)o).longValue();
return null;
}
/** Returns the specified tag's value as a boolean, if possible. */
public boolean getBoolean(int tagType) throws MetadataException
{
Boolean value = getBooleanObject(tagType);
if (value!=null)
return value;
Object o = getObject(tagType);
if (o == null)
throw new MetadataException("Tag '" + getTagName(tagType) + "' has not been set -- check using containsTag() first");
throw new MetadataException("Tag '" + tagType + "' cannot be converted to a boolean. It is of type '" + o.getClass() + "'.");
}
/** Returns the specified tag's value as a boolean. If the tag is not set or cannot be converted, <code>null</code> is returned. */
@Nullable
@SuppressWarnings(value = "NP_BOOLEAN_RETURN_NULL", justification = "keep API interface consistent")
public Boolean getBooleanObject(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof Boolean)
return (Boolean)o;
if (o instanceof String) {
try {
return Boolean.getBoolean((String)o);
} catch (NumberFormatException nfe) {
return null;
}
}
if (o instanceof Number)
return (((Number)o).doubleValue() != 0);
return null;
}
/**
* Returns the specified tag's value as a java.util.Date. If the value is unset or cannot be converted, <code>null</code> is returned.
* <p/>
* If the underlying value is a {@link String}, then attempts will be made to parse the string as though it is in
* the current {@link TimeZone}. If the {@link TimeZone} is known, call the overload that accepts one as an argument.
*/
@Nullable
public java.util.Date getDate(int tagType)
{
return getDate(tagType, null);
}
/**
* Returns the specified tag's value as a java.util.Date. If the value is unset or cannot be converted, <code>null</code> is returned.
* <p/>
* If the underlying value is a {@link String}, then attempts will be made to parse the string as though it is in
* the {@link TimeZone} represented by the {@code timeZone} parameter (if it is non-null). Note that this parameter
* is only considered if the underlying value is a string and parsing occurs, otherwise it has no effect.
*/
@Nullable
public java.util.Date getDate(int tagType, @Nullable TimeZone timeZone)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof java.util.Date)
return (java.util.Date)o;
if (o instanceof String) {
// This seems to cover all known Exif date strings
// Note that " : : : : " is a valid date string according to the Exif spec (which means 'unknown date'): http://www.awaresystems.be/imaging/tiff/tifftags/privateifd/exif/datetimeoriginal.html
String datePatterns[] = {
"yyyy:MM:dd HH:mm:ss",
"yyyy:MM:dd HH:mm",
"yyyy-MM-dd HH:mm:ss",
"yyyy-MM-dd HH:mm",
"yyyy.MM.dd HH:mm:ss",
"yyyy.MM.dd HH:mm" };
String dateString = (String)o;
for (String datePattern : datePatterns) {
try {
DateFormat parser = new SimpleDateFormat(datePattern);
if (timeZone != null)
parser.setTimeZone(timeZone);
return parser.parse(dateString);
} catch (ParseException ex) {
// simply try the next pattern
}
}
}
return null;
}
/** Returns the specified tag's value as a Rational. If the value is unset or cannot be converted, <code>null</code> is returned. */
@Nullable
public Rational getRational(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof Rational)
return (Rational)o;
if (o instanceof Integer)
return new Rational((Integer)o, 1);
if (o instanceof Long)
return new Rational((Long)o, 1);
// NOTE not doing conversions for real number types
return null;
}
/** Returns the specified tag's value as an array of Rational. If the value is unset or cannot be converted, <code>null</code> is returned. */
@Nullable
public Rational[] getRationalArray(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof Rational[])
return (Rational[])o;
return null;
}
/**
* Returns the specified tag's value as a String. This value is the 'raw' value. A more presentable decoding
* of this value may be obtained from the corresponding Descriptor.
*
* @return the String representation of the tag's value, or
* <code>null</code> if the tag hasn't been defined.
*/
@Nullable
public String getString(int tagType)
{
Object o = getObject(tagType);
if (o == null)
return null;
if (o instanceof Rational)
return ((Rational)o).toSimpleString(true);
if (o.getClass().isArray()) {
// handle arrays of objects and primitives
int arrayLength = Array.getLength(o);
final Class<?> componentType = o.getClass().getComponentType();
boolean isObjectArray = Object.class.isAssignableFrom(componentType);
boolean isFloatArray = componentType.getName().equals("float");
boolean isDoubleArray = componentType.getName().equals("double");
boolean isIntArray = componentType.getName().equals("int");
boolean isLongArray = componentType.getName().equals("long");
boolean isByteArray = componentType.getName().equals("byte");
boolean isShortArray = componentType.getName().equals("short");
StringBuilder string = new StringBuilder();
for (int i = 0; i < arrayLength; i++) {
if (i != 0)
string.append(' ');
if (isObjectArray)
string.append(Array.get(o, i).toString());
else if (isIntArray)
string.append(Array.getInt(o, i));
else if (isShortArray)
string.append(Array.getShort(o, i));
else if (isLongArray)
string.append(Array.getLong(o, i));
else if (isFloatArray)
string.append(Array.getFloat(o, i));
else if (isDoubleArray)
string.append(Array.getDouble(o, i));
else if (isByteArray)
string.append(Array.getByte(o, i));
else
addError("Unexpected array component type: " + componentType.getName());
}
return string.toString();
}
// Note that several cameras leave trailing spaces (Olympus, Nikon) but this library is intended to show
// the actual data within the file. It is not inconceivable that whitespace may be significant here, so we
// do not trim. Also, if support is added for writing data back to files, this may cause issues.
// We leave trimming to the presentation layer.
return o.toString();
}
@Nullable
public String getString(int tagType, String charset)
{
byte[] bytes = getByteArray(tagType);
if (bytes==null)
return null;
try {
return new String(bytes, charset);
} catch (UnsupportedEncodingException e) {
return null;
}
}
/**
* Returns the object hashed for the particular tag type specified, if available.
*
* @param tagType the tag type identifier
* @return the tag's value as an Object if available, else <code>null</code>
*/
@java.lang.SuppressWarnings({ "UnnecessaryBoxing" })
@Nullable
public Object getObject(int tagType)
{
return _tagMap.get(Integer.valueOf(tagType));
}
// OTHER METHODS
/**
* Returns the name of a specified tag as a String.
*
* @param tagType the tag type identifier
* @return the tag's name as a String
*/
@NotNull
public String getTagName(int tagType)
{
HashMap<Integer, String> nameMap = getTagNameMap();
if (!nameMap.containsKey(tagType)) {
String hex = Integer.toHexString(tagType);
while (hex.length() < 4) {
hex = "0" + hex;
}
return "Unknown tag (0x" + hex + ")";
}
return nameMap.get(tagType);
}
/**
* Provides a description of a tag's value using the descriptor set by
* <code>setDescriptor(Descriptor)</code>.
*
* @param tagType the tag type identifier
* @return the tag value's description as a String
*/
@Nullable
public String getDescription(int tagType)
{
assert(_descriptor != null);
return _descriptor.getDescription(tagType);
}
}