org.codehaus.jackson.map.introspect.BasicBeanDescription Maven / Gradle / Ivy
package org.codehaus.jackson.map.introspect;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.*;
import org.codehaus.jackson.map.AnnotationIntrospector;
import org.codehaus.jackson.map.BeanDescription;
import org.codehaus.jackson.map.annotate.JsonSerialize;
import org.codehaus.jackson.map.introspect.VisibilityChecker;
import org.codehaus.jackson.map.type.TypeBindings;
import org.codehaus.jackson.map.util.ClassUtil;
import org.codehaus.jackson.type.JavaType;
/**
* Default {@link BeanDescription} implementation.
* Can theoretically be subclassed to customize
* some aspects of property introspection.
*/
public class BasicBeanDescription extends BeanDescription
{
/*
/**********************************************************
/* Configuration
/**********************************************************
*/
/**
* Information collected about the class introspected.
*/
final protected AnnotatedClass _classInfo;
final protected AnnotationIntrospector _annotationIntrospector;
/**
* We may need type bindings for the bean type. If so, we'll
* construct it lazily
*/
protected TypeBindings _bindings;
/*
/**********************************************************
/* Life-cycle
/**********************************************************
*/
public BasicBeanDescription(JavaType type, AnnotatedClass ac,
AnnotationIntrospector ai)
{
super(type);
_classInfo = ac;
_annotationIntrospector = ai;
}
/*
/**********************************************************
/* Simple accessors
/**********************************************************
*/
public AnnotatedClass getClassInfo() { return _classInfo; }
/**
* Method for checking whether class being described has any
* annotations recognized by registered annotation introspector.
*/
public boolean hasKnownClassAnnotations() {
return _classInfo.hasAnnotations();
}
public AnnotatedMethod findMethod(String name, Class[] paramTypes)
{
return _classInfo.findMethod(name, paramTypes);
}
/**
* @param fixAccess If true, method is allowed to fix access to the
* default constructor (to be able to call non-public constructor);
* if false, has to use constructor as is.
*
* @return Instance of class represented by this descriptor, if
* suitable default constructor was found; null otherwise.
*/
public Object instantiateBean(boolean fixAccess)
{
AnnotatedConstructor ac = _classInfo.getDefaultConstructor();
if (ac == null) {
return null;
}
if (fixAccess) {
ac.fixAccess();
}
try {
return ac.getAnnotated().newInstance();
} catch (Exception e) {
Throwable t = e;
while (t.getCause() != null) {
t = t.getCause();
}
if (t instanceof Error) throw (Error) t;
if (t instanceof RuntimeException) throw (RuntimeException) t;
throw new IllegalArgumentException("Failed to instantiate bean of type "+_classInfo.getAnnotated().getName()+": ("+t.getClass().getName()+") "+t.getMessage(), t);
}
}
public TypeBindings bindingsForBeanType()
{
if (_bindings == null) {
_bindings = new TypeBindings(_type);
}
return _bindings;
}
/*
/**********************************************************
/* Basic API
/**********************************************************
*/
/*
/**********************************************************
/* Introspection for serialization (write JSON), getters
/**********************************************************
*/
@Override
public LinkedHashMap findGetters(VisibilityChecker visibilityChecker,
Collection ignoredProperties)
{
LinkedHashMap results = new LinkedHashMap();
for (AnnotatedMethod am : _classInfo.memberMethods()) {
/* note: signature has already been checked to some degree
* via filters; however, no checks were done for arg count
*/
// 16-May-2009, tatu: JsonIgnore processed earlier already
if (am.getParameterCount() != 0) {
continue;
}
/* So far so good: final check, then; has to either
* (a) be marked with JsonProperty (/JsonGetter/JsonSerialize) OR
* (b) be public AND have suitable name (getXxx or isXxx)
*/
String propName = _annotationIntrospector.findGettablePropertyName(am);
if (propName != null) {
/* As per [JACKSON-64], let's still use mangled
* name if possible; and only if not use unmodified
* method name
*/
if (propName.length() == 0) {
propName = okNameForAnyGetter(am, am.getName());
if (propName == null) {
propName = am.getName();
}
}
} else {
propName = am.getName();
// [JACKSON-166], need to separate getXxx/isXxx methods
if (propName.startsWith("get")) { // nope, but is public bean-getter name?
if (!visibilityChecker.isGetterVisible(am)) {
continue;
}
propName = okNameForGetter(am, propName);
} else {
if (!visibilityChecker.isIsGetterVisible(am)) {
continue;
}
propName = okNameForIsGetter(am, propName);
}
// null return value means 'not valid'
if (propName == null) continue;
// [JACKSON-384] Plus, should not include "AnyGetter" as regular getter..
if (_annotationIntrospector.hasAnyGetterAnnotation(am)) continue;
}
if (ignoredProperties != null) {
if (ignoredProperties.contains(propName)) {
continue;
}
}
/* Yup, it is a valid name. But now... do we have a conflict?
* If so, should throw an exception
*/
AnnotatedMethod old = results.put(propName, am);
if (old != null) {
String oldDesc = old.getFullName();
String newDesc = am.getFullName();
throw new IllegalArgumentException("Conflicting getter definitions for property \""+propName+"\": "+oldDesc+" vs "+newDesc);
}
}
return results;
}
/**
* Method for locating the getter method that is annotated with
* {@link org.codehaus.jackson.annotate.JsonValue} annotation,
* if any. If multiple ones are found,
* an error is reported by throwing {@link IllegalArgumentException}
*/
public AnnotatedMethod findJsonValueMethod()
{
AnnotatedMethod found = null;
for (AnnotatedMethod am : _classInfo.memberMethods()) {
// must be marked with "JsonValue" (or similar)
if (!_annotationIntrospector.hasAsValueAnnotation(am)) {
continue;
}
if (found != null) {
throw new IllegalArgumentException("Multiple methods with active 'as-value' annotation ("+found.getName()+"(), "+am.getName()+")");
}
// Also, must have getter signature
/* 18-May-2009, tatu: Should this be moved to annotation
* introspector, to give better error message(s)? For now
* will leave here, may want to reconsider in future.
*/
if (!ClassUtil.hasGetterSignature(am.getAnnotated())) {
throw new IllegalArgumentException("Method "+am.getName()+"() marked with an 'as-value' annotation, but does not have valid getter signature (non-static, takes no args, returns a value)");
}
found = am;
}
return found;
}
/*
/**********************************************************
/* Introspection for serialization, factories
/**********************************************************
*/
/**
* Method that will locate the no-arg constructor for this class,
* if it has one, and that constructor has not been marked as
* ignorable.
* Method will also ensure that the constructor is accessible.
*/
public Constructor findDefaultConstructor()
{
AnnotatedConstructor ac = _classInfo.getDefaultConstructor();
if (ac == null) {
return null;
}
return ac.getAnnotated();
}
public List getConstructors()
{
return _classInfo.getConstructors();
}
public List getFactoryMethods()
{
// must filter out anything that clearly is not a factory method
List candidates = _classInfo.getStaticMethods();
if (candidates.isEmpty()) {
return candidates;
}
ArrayList result = new ArrayList();
for (AnnotatedMethod am : candidates) {
if (isFactoryMethod(am)) {
result.add(am);
}
}
return result;
}
/**
* Method that can be called to locate a single-arg constructor that
* takes specified exact type (will not accept supertype constructors)
*
* @param argTypes Type(s) of the argument that we are looking for
*/
public Constructor findSingleArgConstructor(Class... argTypes)
{
for (AnnotatedConstructor ac : _classInfo.getConstructors()) {
// This list is already filtered to only include accessible
/* (note: for now this is a redundant check; but in future
* that may change; thus leaving here for now)
*/
if (ac.getParameterCount() == 1) {
Class actArg = ac.getParameterClass(0);
for (Class expArg : argTypes) {
if (expArg == actArg) {
return ac.getAnnotated();
}
}
}
}
return null;
}
/**
* Method that can be called to find if introspected class declares
* a static "valueOf" factory method that returns an instance of
* introspected type, given one of acceptable types.
*
* @param expArgTypes Types that the matching single argument factory
* method can take: will also accept super types of these types
* (ie. arg just has to be assignable from expArgType)
*/
public Method findFactoryMethod(Class... expArgTypes)
{
// So, of all single-arg static methods:
for (AnnotatedMethod am : _classInfo.getStaticMethods()) {
if (isFactoryMethod(am)) {
// And must take one of expected arg types (or supertype)
Class actualArgType = am.getParameterClass(0);
for (Class expArgType : expArgTypes) {
// And one that matches what we would pass in
if (actualArgType.isAssignableFrom(expArgType)) {
return am.getAnnotated();
}
}
}
}
return null;
}
protected boolean isFactoryMethod(AnnotatedMethod am)
{
/* First: return type must be compatible with the introspected class
* (i.e. allowed to be sub-class, although usually is the same
* class)
*/
Class rt = am.getRawType();
if (!getBeanClass().isAssignableFrom(rt)) {
return false;
}
/* Also: must be a recognized factory method, meaning:
* (a) marked with @JsonCreator annotation, or
* (a) "valueOf" (at this point, need not be public)
*/
if (_annotationIntrospector.hasCreatorAnnotation(am)) {
return true;
}
if ("valueOf".equals(am.getName())) {
return true;
}
return false;
}
/**
* Method for getting ordered list of named Creator properties.
* Returns an empty list is none found. If multiple Creator
* methods are defined, order between properties from different
* methods is undefined; however, properties for each such
* Creator are ordered properly relative to each other. For the
* usual case of just a single Creator, named properties are
* thus properly ordered.
*/
public List findCreatorPropertyNames()
{
List names = null;
for (int i = 0; i < 2; ++i) {
List l = (i == 0)
? getConstructors() : getFactoryMethods();
for (AnnotatedWithParams creator : l) {
int argCount = creator.getParameterCount();
if (argCount < 1) continue;
String name = _annotationIntrospector.findPropertyNameForParam(creator.getParameter(0));
if (name == null) continue;
if (names == null) {
names = new ArrayList();
}
names.add(name);
for (int p = 1; p < argCount; ++p) {
names.add(_annotationIntrospector.findPropertyNameForParam(creator.getParameter(p)));
}
}
}
if (names == null) {
return Collections.emptyList();
}
return names;
}
/*
/**********************************************************
/* Introspection for serialization, fields
/**********************************************************
*/
public LinkedHashMap findSerializableFields(VisibilityChecker vchecker,
Collection ignoredProperties)
{
return _findPropertyFields(vchecker, ignoredProperties, true);
}
/*
/**********************************************************
/* Introspection for serialization, other
/**********************************************************
*/
/**
* Method for determining whether null properties should be written
* out for a Bean of introspected type. This is based on global
* feature (lowest priority, passed as argument)
* and per-class annotation (highest priority).
*/
public JsonSerialize.Inclusion findSerializationInclusion(JsonSerialize.Inclusion defValue)
{
return _annotationIntrospector.findSerializationInclusion(_classInfo, defValue);
}
/*
/**********************************************************
/* Introspection for deserialization, setters:
/**********************************************************
*/
@Override
public LinkedHashMap findSetters(VisibilityChecker vchecker)
{
LinkedHashMap results = new LinkedHashMap();
for (AnnotatedMethod am : _classInfo.memberMethods()) {
// note: signature has already been checked via filters
// Arg count != 1 (JsonIgnore checked earlier)
if (am.getParameterCount() != 1) {
continue;
}
/* So far so good: final check, then; has to either
* (a) be marked with JsonProperty (/JsonSetter/JsonDeserialize) OR
* (b) have suitable name (setXxx) (NOTE: need not be
* public, unlike with getters)
*/
String propName = _annotationIntrospector.findSettablePropertyName(am);
if (propName != null) { // annotation was found
/* As per [JACKSON-64], let's still use mangled name if
* possible; and only if not use unmodified method name
*/
if (propName.length() == 0) {
propName = okNameForSetter(am);
// null means it's not named as a Bean getter; fine, use as is
if (propName == null) {
propName = am.getName();
}
}
} else { // nope, but is public bean-setter name?
if (!vchecker.isSetterVisible(am)) {
continue;
}
propName = okNameForSetter(am);
if (propName == null) { // null means 'not valid'
continue;
}
}
/* Yup, it is a valid name. But now... do we have a conflict?
* If so, should throw an exception
*/
AnnotatedMethod old = results.put(propName, am);
if (old != null) {
/* [JACKSON-255] Only throw exception if they are in same class. Must
* be careful to choose "correct" one; first one should actually
* have priority
*
*/
if (old.getDeclaringClass() == am.getDeclaringClass()) {
String oldDesc = old.getFullName();
String newDesc = am.getFullName();
throw new IllegalArgumentException("Conflicting setter definitions for property \""+propName+"\": "+oldDesc+" vs "+newDesc);
}
// to put earlier one back
results.put(propName, old);
}
}
return results;
}
/**
* Method used to locate the method of introspected class that
* implements {@link org.codehaus.jackson.annotate.JsonAnySetter}. If no such method exists
* null is returned. If more than one are found, an exception
* is thrown.
* Additional checks are also made to see that method signature
* is acceptable: needs to take 2 arguments, first one String or
* Object; second any can be any type.
*/
public AnnotatedMethod findAnySetter()
throws IllegalArgumentException
{
AnnotatedMethod found = null;
for (AnnotatedMethod am : _classInfo.memberMethods()) {
if (!_annotationIntrospector.hasAnySetterAnnotation(am)) {
continue;
}
if (found != null) {
throw new IllegalArgumentException("Multiple methods with 'any-setter' annotation ("+found.getName()+"(), "+am.getName()+")");
}
int pcount = am.getParameterCount();
if (pcount != 2) {
throw new IllegalArgumentException("Invalid 'any-setter' annotation on method "+am.getName()+"(): takes "+pcount+" parameters, should take 2");
}
/* Also, let's be somewhat strict on how field name is to be
* passed; String, Object make sense, others not
* so much.
*/
/* !!! 18-May-2009, tatu: how about enums? Can add support if
* requested; easy enough for devs to add support within
* method.
*/
Class type = am.getParameterClass(0);
if (type != String.class && type != Object.class) {
throw new IllegalArgumentException("Invalid 'any-setter' annotation on method "+am.getName()+"(): first argument not of type String or Object, but "+type.getName());
}
found = am;
}
return found;
}
/**
* Method used to locate the method of introspected class that
* implements {@link org.codehaus.jackson.annotate.JsonAnyGetter}.
* If no such method exists null is returned.
* If more than one are found, an exception is thrown.
*
* @since 1.6
*/
public AnnotatedMethod findAnyGetter() throws IllegalArgumentException
{
AnnotatedMethod found = null;
for (AnnotatedMethod am : _classInfo.memberMethods()) {
if (!_annotationIntrospector.hasAnyGetterAnnotation(am)) {
continue;
}
if (found != null) {
throw new IllegalArgumentException("Multiple methods with 'any-getter' annotation ("+found.getName()+"(), "+am.getName()+")");
}
/* For now let's require a Map; in future can add support for other
* types like perhaps Iterable?
*/
Class type = am.getRawType();
if (!Map.class.isAssignableFrom(type)) {
throw new IllegalArgumentException("Invalid 'any-getter' annotation on method "+am.getName()+"(): return type is not instance of java.util.Map");
}
found = am;
}
return found;
}
/**
* Method for locating all back-reference properties (setters, fields) bean has
*
* @since 1.6
*/
public Map findBackReferenceProperties()
{
HashMap result = null;
// First, gather setter methods
for (AnnotatedMethod am : _classInfo.memberMethods()) {
if (am.getParameterCount() == 1) {
AnnotationIntrospector.ReferenceProperty prop = _annotationIntrospector.findReferenceType(am);
if (prop != null && prop.isBackReference()) {
if (result == null) {
result = new HashMap();
}
if (result.put(prop.getName(), am) != null) {
throw new IllegalArgumentException("Multiple back-reference properties with name '"+prop.getName()+"'");
}
}
}
}
// then settable fields
for (AnnotatedField af : _classInfo.fields()) {
AnnotationIntrospector.ReferenceProperty prop = _annotationIntrospector.findReferenceType(af);
if (prop != null && prop.isBackReference()) {
if (result == null) {
result = new HashMap();
}
if (result.put(prop.getName(), af) != null) {
throw new IllegalArgumentException("Multiple back-reference properties with name '"+prop.getName()+"'");
}
}
}
return result;
}
/*
/**********************************************************
/* Introspection for deserialization, fields:
/**********************************************************
*/
public LinkedHashMap findDeserializableFields(VisibilityChecker vchecker,
Collection ignoredProperties)
{
return _findPropertyFields(vchecker, ignoredProperties, false);
}
/*
/**********************************************************
/* Helper methods for getters
/**********************************************************
*/
public String okNameForAnyGetter(AnnotatedMethod am, String name)
{
String str = okNameForIsGetter(am, name);
if (str == null) {
str = okNameForGetter(am, name);
}
return str;
}
public String okNameForGetter(AnnotatedMethod am, String name)
{
if (name.startsWith("get")) {
/* 16-Feb-2009, tatu: To handle [JACKSON-53], need to block
* CGLib-provided method "getCallbacks". Not sure of exact
* safe critieria to get decent coverage without false matches;
* but for now let's assume there's no reason to use any
* such getter from CGLib.
* But let's try this approach...
*/
if ("getCallbacks".equals(name)) {
if (isCglibGetCallbacks(am)) {
return null;
}
} else if ("getMetaClass".equals(name)) {
/* 30-Apr-2009, tatu: [JACKSON-103], need to suppress
* serialization of a cyclic (and useless) reference
*/
if (isGroovyMetaClassGetter(am)) {
return null;
}
}
return mangleGetterName(am, name.substring(3));
}
return null;
}
public String okNameForIsGetter(AnnotatedMethod am, String name)
{
if (name.startsWith("is")) {
// plus, must return boolean...
Class rt = am.getRawType();
if (rt != Boolean.class && rt != Boolean.TYPE) {
return null;
}
return mangleGetterName(am, name.substring(2));
}
// no, not a match by name
return null;
}
/**
* @return Null to indicate that method is not a valid accessor;
* otherwise name of the property it is accessor for
*/
protected String mangleGetterName(Annotated a, String basename)
{
return manglePropertyName(basename);
}
/**
* This method was added to address [JACKSON-53]: need to weed out
* CGLib-injected "getCallbacks".
* At this point caller has detected a potential getter method
* with name "getCallbacks" and we need to determine if it is
* indeed injectect by Cglib. We do this by verifying that the
* result type is "net.sf.cglib.proxy.Callback[]"
*
* Also, see [JACKSON-177]; Hibernate may repackage cglib
* it uses, so we better catch that too
*/
protected boolean isCglibGetCallbacks(AnnotatedMethod am)
{
Class rt = am.getRawType();
// Ok, first: must return an array type
if (rt == null || !rt.isArray()) {
return false;
}
/* And that type needs to be "net.sf.cglib.proxy.Callback".
* Theoretically could just be a type that implements it, but
* for now let's keep things simple, fix if need be.
*/
Class compType = rt.getComponentType();
// Actually, let's just verify it's a "net.sf.cglib.*" class/interface
Package pkg = compType.getPackage();
if (pkg != null) {
String pname = pkg.getName();
if (pname.startsWith("net.sf.cglib")
// also, as per [JACKSON-177]
|| pname.startsWith("org.hibernate.repackage.cglib")) {
return true;
}
}
return false;
}
/**
* Similar to {@link #isCglibGetCallbacks}, need to suppress
* a cyclic reference to resolve [JACKSON-103]
*/
protected boolean isGroovyMetaClassSetter(AnnotatedMethod am)
{
Class argType = am.getParameterClass(0);
Package pkg = argType.getPackage();
if (pkg != null && pkg.getName().startsWith("groovy.lang")) {
return true;
}
return false;
}
/**
* Another helper method to deal with rest of [JACKSON-103]
*/
protected boolean isGroovyMetaClassGetter(AnnotatedMethod am)
{
Class rt = am.getRawType();
if (rt == null || rt.isArray()) {
return false;
}
Package pkg = rt.getPackage();
if (pkg != null && pkg.getName().startsWith("groovy.lang")) {
return true;
}
return false;
}
/*
/**********************************************************
/* Helper methods for setters
/**********************************************************
*/
public String okNameForSetter(AnnotatedMethod am)
{
String name = am.getName();
/* For mutators, let's not require it to be public. Just need
* to be able to call it, i.e. do need to 'fix' access if so
* (which is done at a later point as needed)
*/
if (name.startsWith("set")) {
name = mangleSetterName(am, name.substring(3));
if (name == null) { // plain old "set" is no good...
return null;
}
if ("metaClass".equals(name)) {
// 26-Nov-2009 [JACSON-103], need to suppress this internal groovy method
if (isGroovyMetaClassSetter(am)) {
return null;
}
}
return name;
}
return null;
}
/**
* @return Null to indicate that method is not a valid accessor;
* otherwise name of the property it is accessor for
*/
protected String mangleSetterName(Annotated a, String basename)
{
return manglePropertyName(basename);
}
/*
/**********************************************************
/* Helper methods for field introspection
/**********************************************************
*/
/**
* @param vchecker (optional) Object that determines whether specific fields
* have enough visibility to be considered for inclusion; if null,
* auto-detection is disabled
* @param ignoredProperties (optional) names of properties to ignore;
* any fields that would be recognized as one of these properties
* is ignored.
* @param forSerialization If true, will collect serializable property
* fields; if false, deserializable
*
* @return Ordered Map with logical property name as key, and
* matching field as value.
*/
public LinkedHashMap _findPropertyFields(VisibilityChecker vchecker,
Collection ignoredProperties,
boolean forSerialization)
{
LinkedHashMap results = new LinkedHashMap();
for (AnnotatedField af : _classInfo.fields()) {
/* note: some pre-filtering has been; no static or transient fields
* included; nor anything marked as ignorable (@JsonIgnore).
* Field masking has also been resolved, but it is still possible
* to get conflicts due to logical name overwrites.
*/
/* So far so good: final check, then; has to either
* (a) be marked with JsonProperty (or JsonSerialize) OR
* (b) be public
*/
String propName = forSerialization
? _annotationIntrospector.findSerializablePropertyName(af)
: _annotationIntrospector.findDeserializablePropertyName(af)
;
if (propName != null) { // is annotated
if (propName.length() == 0) {
propName = af.getName();
}
} else { // nope, but may be visible (usually, public, can be recofingured)
if (!vchecker.isFieldVisible(af)) {
continue;
}
propName = af.getName();
}
if (ignoredProperties != null) {
if (ignoredProperties.contains(propName)) {
continue;
}
}
/* Yup, it is a valid name. But do we have a conflict?
* Shouldn't usually happen, but it is possible... and for
* now let's consider it a problem
*/
AnnotatedField old = results.put(propName, af);
if (old != null) {
/* 21-Feb-2010, tatus: Not necessarily a conflict, still; only
* conflict if these are declared in same class (in future, might
* not even be conflict then, if types are different? That would
* allow "union" types. But for now, let's consider that illegale
* to keep things simple.
*/
/* Note: we assume that fields are ordered from "oldest" (super-class) to
* "newest" (sub-classes); this should guarantee proper ordering
*/
if (old.getDeclaringClass() == af.getDeclaringClass()) {
String oldDesc = old.getFullName();
String newDesc = af.getFullName();
throw new IllegalArgumentException("Multiple fields representing property \""+propName+"\": "+oldDesc+" vs "+newDesc);
}
}
}
return results;
}
/*
/**********************************************************
/* Property name mangling (getFoo -> foo)
/**********************************************************
*/
/**
* Method called to figure out name of the property, given
* corresponding suggested name based on a method or field name.
*
* @param basename Name of accessor/mutator method, not including prefix
* ("get"/"is"/"set")
*/
public static String manglePropertyName(String basename)
{
int len = basename.length();
// First things first: empty basename is no good
if (len == 0) {
return null;
}
// otherwise, lower case initial chars
StringBuilder sb = null;
for (int i = 0; i < len; ++i) {
char upper = basename.charAt(i);
char lower = Character.toLowerCase(upper);
if (upper == lower) {
break;
}
if (sb == null) {
sb = new StringBuilder(basename);
}
sb.setCharAt(i, lower);
}
return (sb == null) ? basename : sb.toString();
}
/**
* Helper method used to describe an annotated element of type
* {@link Class} or {@link Method}.
*/
public static String descFor(AnnotatedElement elem)
{
if (elem instanceof Class) {
return "class "+((Class) elem).getName();
}
if (elem instanceof Method) {
Method m = (Method) elem;
return "method "+m.getName()+" (from class "+m.getDeclaringClass().getName()+")";
}
if (elem instanceof Constructor) {
Constructor ctor = (Constructor) elem;
// should indicate number of args?
return "constructor() (from class "+ctor.getDeclaringClass().getName()+")";
}
// what else?
return "unknown type ["+elem.getClass()+"]";
}
}