I m not at all sure that this is even a solvable problem, but supposing that I have a freemarker template, I d like to be able to ask the template what variables it uses.
For my purposes, we can assume that the freemarker template is very simple - just "root level" entries (the model for such a template could be a simple Map). In other words, I don t need to handle templates that call for nested structures, etc.
I had the same task to get the list of variables from template on java side and don t found any good approaches to that except using reflection. I m not sure whether there is a better way to get this data or not but here s my approach:
public Set<String> referenceSet(Template template) throws TemplateModelException {
Set<String> result = new HashSet<>();
TemplateElement rootTreeNode = template.getRootTreeNode();
for (int i = 0; i < rootTreeNode.getChildCount(); i++) {
TemplateModel templateModel = rootTreeNode.getChildNodes().get(i);
if (!(templateModel instanceof StringModel)) {
continue;
}
Object wrappedObject = ((StringModel) templateModel).getWrappedObject();
if (!"DollarVariable".equals(wrappedObject.getClass().getSimpleName())) {
continue;
}
try {
Object expression = getInternalState(wrappedObject, "expression");
switch (expression.getClass().getSimpleName()) {
case "Identifier":
result.add(getInternalState(expression, "name").toString());
break;
case "DefaultToExpression":
result.add(getInternalState(expression, "lho").toString());
break;
case "BuiltinVariable":
break;
default:
throw new IllegalStateException("Unable to introspect variable");
}
} catch (NoSuchFieldException | IllegalAccessException e) {
throw new TemplateModelException("Unable to reflect template model");
}
}
return result;
}
private Object getInternalState(Object o, String fieldName) throws NoSuchFieldException, IllegalAccessException {
Field field = o.getClass().getDeclaredField(fieldName);
boolean wasAccessible = field.isAccessible();
try {
field.setAccessible(true);
return field.get(o);
} finally {
field.setAccessible(wasAccessible);
}
}
Sample project that I made for demonstrating template introspection can be found on github: https://github.com/SimY4/TemplatesPOC.git
one other way to get the variables from java. This just tries to process the template and catch the InvalidReferenceException to find all the variables in a freemarker-template
/**
* Find all the variables used in the Freemarker Template
* @param templateName
* @return
*/
public Set<String> getTemplateVariables(String templateName) {
Template template = getTemplate(templateName);
StringWriter stringWriter = new StringWriter();
Map<String, Object> dataModel = new HashMap<>();
boolean exceptionCaught;
do {
exceptionCaught = false;
try {
template.process(dataModel, stringWriter);
} catch (InvalidReferenceException e) {
exceptionCaught = true;
dataModel.put(e.getBlamedExpressionString(), "");
} catch (IOException | TemplateException e) {
throw new IllegalStateException("Failed to Load Template: " + templateName, e);
}
} while (exceptionCaught);
return dataModel.keySet();
}
private Template getTemplate(String templateName) {
try {
return configuration.getTemplate(templateName);
} catch (IOException e) {
throw new IllegalStateException("Failed to Load Template: " + templateName, e);
}
}
This is probably late, but in case anyone else encountered this problem : you can use data_model and globals to inspect the model - data_model will only contain values provided by the model while globals will also contain any variables defined in the template. You need to prepend the special variables with a dot - so to access globals, use ${.globals}
For other special variables see http://freemarker.sourceforge.net/docs/ref_specvar.html
I solved this for my very simple usecase (only using flat datastructure, no nesting (for example: ${parent.child}), lists or more specific) with dummy data provider:
public class DummyDataProvider<K, V> extends HashMap<K, V> {
private static final long serialVersionUID = 1;
public final Set<String> variables = new HashSet<>();
@SuppressWarnings("unchecked")
@Override
public V get(Object key) {
variables.add(key.toString());
return (V) key;
}
}
You can give this for processing to a template and when it finishes Set variables contains your variables.
This is very simplistic approach, which certainly needs improvement, but you get the idea.
public static Set<String> getNecessaryTemplateVariables(String templateName) throws TemplateModelException {
Set<String> result = new HashSet<>();
TemplateElement rootTreeNode = getTemplate(templateName).getRootTreeNode();
if ("IteratorBlock".equals(rootTreeNode.getClass().getSimpleName())) {
introspectFromIteratorBlock(result, rootTreeNode);
return result;
}
for (int i = 0; i < rootTreeNode.getChildCount(); i++) {
TemplateModel templateModel = rootTreeNode.getChildNodes().get(i);
if (!(templateModel instanceof StringModel)) {
continue;
}
Object wrappedObject = ((StringModel) templateModel).getWrappedObject();
if ("DollarVariable".equals(wrappedObject.getClass().getSimpleName())) {
introspectFromDollarVariable(result, wrappedObject);
} else if ("ConditionalBlock".equals(wrappedObject.getClass().getSimpleName())) {
introspectFromConditionalBlock(result, wrappedObject);
} else if ("IfBlock".equals(wrappedObject.getClass().getSimpleName())) {
introspectFromIfBlock(result, wrappedObject);
} else if ("IteratorBlock".equals(wrappedObject.getClass().getSimpleName())) {
introspectFromIteratorBlock(result, wrappedObject);
}
}
return result;
}
private static void introspectFromIteratorBlock(Set<String> result, Object wrappedObject) {
try {
Object expression = getInternalState(wrappedObject, "listExp");
result.add(getInternalState(expression, "name").toString());
} catch (NoSuchFieldException | IllegalAccessException ignored) {
}
}
private static void introspectFromConditionalBlock(Set<String> result, Object wrappedObject)
throws TemplateModelException {
try {
Object expression = getInternalState(wrappedObject, "condition");
if (expression == null) {
return;
}
result.addAll(dealCommonExpression(expression));
String nested = getInternalState(wrappedObject, "nestedBlock").toString();
result.addAll(getNecessaryTemplateVariables(nested));
} catch (NoSuchFieldException | IllegalAccessException ignored) {
}
}
private static Set<String> dealCommonExpression(Object expression)
throws NoSuchFieldException, IllegalAccessException {
Set<String> ret = Sets.newHashSet();
switch (expression.getClass().getSimpleName()) {
case "ComparisonExpression":
String reference = dealComparisonExpression(expression);
ret.add(reference);
break;
case "ExistsExpression":
reference = dealExistsExpression(expression);
ret.add(reference);
break;
case "AndExpression":
ret.addAll(dealAndExpression(expression));
default:
break;
}
return ret;
}
private static String dealComparisonExpression(Object expression)
throws NoSuchFieldException, IllegalAccessException {
Object left = getInternalState(expression, "left");
Object right = getInternalState(expression, "right");
String reference;
if ("Identifier".equals(left.getClass().getSimpleName())) {
reference = getInternalState(left, "name").toString();
} else {
reference = getInternalState(right, "name").toString();
}
return reference;
}
private static String dealExistsExpression(Object expression) throws NoSuchFieldException, IllegalAccessException {
Object exp = getInternalState(expression, "exp");
return getInternalState(exp, "name").toString();
}
private static Set<String> dealAndExpression(Object expression) throws NoSuchFieldException,
IllegalAccessException{
Set<String> ret = Sets.newHashSet();
Object lho = getInternalState(expression, "lho");
ret.addAll(dealCommonExpression(lho));
Object rho = getInternalState(expression, "rho");
ret.addAll(dealCommonExpression(rho));
return ret;
}
private static void introspectFromIfBlock(Set<String> result, Object wrappedObject)
throws TemplateModelException {
result.addAll(getNecessaryTemplateVariables(wrappedObject.toString()));
}
private static void introspectFromDollarVariable(Set<String> result, Object wrappedObject)
throws TemplateModelException {
try {
Object expression = getInternalState(wrappedObject, "expression");
switch (expression.getClass().getSimpleName()) {
case "Identifier":
result.add(getInternalState(expression, "name").toString());
break;
case "DefaultToExpression":
result.add(getInternalState(expression, "lho").toString());
break;
case "BuiltinVariable":
break;
default:
break;
}
} catch (NoSuchFieldException | IllegalAccessException e) {
throw new TemplateModelException("Unable to reflect template model");
}
}
private static Object getInternalState(Object o, String fieldName) throws NoSuchFieldException, IllegalAccessException {
Field [] fieldArray = o.getClass().getDeclaredFields();
for (Field field : fieldArray) {
if (!field.getName().equals(fieldName)) {
continue;
}
boolean wasAccessible = field.isAccessible();
try {
field.setAccessible(true);
return field.get(o);
} finally {
field.setAccessible(wasAccessible);
}
}
throw new NoSuchFieldException();
}
private static Template getTemplate(String templateName) {
try {
StringReader stringReader = new StringReader(templateName);
return new Template(null, stringReader, null);
} catch (IOException e) {
throw new IllegalStateException("Failed to Load Template: " + templateName, e);
}
}
I optimized SimY4 s answer, and supported <#list> and <#if> block. Code is not fully tested
Execute following regex on the template:
(?<=${)([^}]+)(?=})
I had the same problem and none of posted solution made sense to me. What I came with is plugging custom implementation of
TemplateExceptionHandler. Example:
final private List<String> missingReferences = Lists.newArrayList();
final Configuration cfg = new Configuration(Configuration.VERSION_2_3_23);
cfg.setTemplateExceptionHandler(new TemplateExceptionHandler() {
@Override
public void handleTemplateException(TemplateException arg0, Environment arg1, Writer arg2) throws TemplateException {
if (arg0 instanceof InvalidReferenceException) {
missingReferences.add(arg0.getBlamedExpressionString());
return;
}
throw arg0;
}
}
Template template = loadTemplate(cfg, templateId, templateText);
StringWriter out = new StringWriter();
try {
template.process(templateData, out);
} catch (TemplateException | IOException e) {
throw new RuntimeException("oops", e);
}
System.out.println("Missing references: " + missingReferences);
Read more here: https://freemarker.apache.org/docs/pgui_config_errorhandling.html
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