If you have a method then you can use the method call operation on it. The method call operation is a comma-separated list of expressions in parentheses. These values are called parameters. The method call operation passes these values to the method which will in turn return a result.
This result will be the value of the whole method call expression. For example, assume the programmers have made available a method variable called repeat.
You give a string as the first parameter, and a number as the second parameter, and it returns a string which repeats the first parameter the number of times specified by the second parameter.
Here repeat was evaluated to the method variable according to how you access top-level variables and then "What", 3 invoked that method. I would like to emphasize that method calls are just plain expressions, like everything else. So this:. These operators exist since FreeMarker 2. As we explained earlier, an error will occur and abort the template processing if you try to access a missing variable.
However two special operators can suppress this error, and handle the problematic situation. The handled variable can be top-level variable, hash subvariable, or sequence subvariable as well. Furthermore these operators handle the situation when a method call doesn't return a value from the viewpoint of Java programmers: it returns null or it's return type is void , so it's more correct to say that these operators handle missing values in general, rather than just missing variables.
For those who know what's Java null , FreeMarker 2. Simply, the template language doesn't know the concept of null. For example, if you have a bean that has a maidenName property, and the value of that property is null , then that's the same as if there were no such property at all, as far as the template is concerned assuming you didn't configured FreeMarker to use some extreme object wrapper, that is. The result of a method call that returns null is also treated as a missing variable again, assuming that you use some usual object wrapper.
See more in the FAQ. This operator allows you to specify a default value for the case when the value is missing. Assume no variable called mouse is present:. The default value can be any kind of expression, so it doesn't have to be a string. For example you can write hits! There is no restriction regarding the complexity of the expression that specifies the default value, for example you can write: cargo. If you have a composite expression after the!
That's needed because due to a programming mistake in FreeMarker 2. This programming error will be fixed in FreeMarker 2. If the default value is omitted, then it will be empty string and empty sequence and empty hash at the same time. This is possible because FreeMarker allows multi-type values. Note the consequence that you can't omit the default value if you want it to be 0 or false.
This will handle if color is missing inside product and returns "red" if so , but will not handle if product is missing.
That is, the product variable itself must exist, otherwise the template processing will die with error. This will handle if product.
That is, if product is missing, or product exists but it does not contain color , the result will be "red" , and no error will occur.
The important difference between this and the previous example is that when surrounded with parentheses, it is allowed for any component of the expression to be undefined, while without parentheses only the last component of the expression is allowed to be undefined. Of course, the default value operator can be used with sequence sub variables as well:. A negative sequence index as seq[-1]!
This operator tells if a value is missing or not. Depending on that, the result is either true or false. With non-top-level variables the rules are the same as with the default value operator, that is, you can write product. These are actually not expressions, but parts of the syntax of the assignment directives, such as assign , local and global. As such, they can't be used anywhere else. FreeMarker doesn't support general purpose lambdas unlike Java.
Hence, and to differentiate them from "real" lambdas, these are called local lambdas. The syntax of lambdas is like name1 , name2 , In that case though, you don't need a lambda expression, as all built-ins that support a lambda parameter, also support passing in a function directly.
For example, instead of seq? The argument specified in a lambda expression can hold the missing Java null value. Reading a lambda argument never falls back to higher scope, so a variable with identical name will not interfere when accessing the lambda parameter.
Therefore something like seq? Note that the parentheses of a method call expressions have nothing to do with the parentheses used for grouping. FTL ignores superfluous white-space in expressions. So these are totally equivalent:.
Expression may contain comments anywhere where they can contain ignored white-space see above. If you really need the XML wrapping facility, review carefully what XPath expressions are possible in your setup. Also, be sure you don't use the long deprecated, and more dangerous freemarker. Also, note that when using the XML wrapping feature, not allowing org. Node methods in the MemberAccessPolicy has no effect, since it doesn't expose Java Node members to templates directly.
Last not least, some maybe aware of the historical legacy that standard object wrappers filter out some well known "unsafe" methods, like System. Do not ever rely on that, since it only blocks the methods from a small predefined list. Clearly it's impossible to blacklist all the problematic members in those. Template-loader Configuration. To avoid loading sensitive data, you have to use a TemplateLoader that double-checks that the file to load is something that should be exposed.
Note that freemarker. The new built-in Configuration. While new will not instantiate classes that are not TemplateModel -s, FreeMarker contains a TemplateModel class that can be used to create arbitrary Java objects.
Other "dangerous" TemplateModel -s can exist in you class-path. Plus, even if a class doesn't implement TemplateModel , its static initialization will be run. To avoid these, you should use a TemplateClassResolver that restricts the accessible classes to the absolute minimum possibly based on which template asks for them , such as TemplateClassResolver.
Do not use TemplateClassResolver. Note that if, and only if your ObjectWrapper is a BeansWrapper or a subclass of it typically DefaultObjectWrapper , constructors not allowed by the MemberAccessPolicy also won't be accessible for? Denial-of-Service DoS attacks: It's trivial to create templates that run practically forever with a loop , or exhaust memory by concatenating to a string in a loop.
FreeMarker can't enforce CPU or memory usage limits, so this is something that has no solution on the FreeMarker-level. It's not possible yet , but something very similar is possible if you write a class that implements freemarker. TemplateMethodModelEx or freemarker. YourClass "? Note that using the assign directive for this works because functions and methods and macros are just plain variables in FreeMarker. For the same reason you could also put TemplateMethodModelEx or TemplateDirectiveModel instances into the data-model before calling the template, or into the shared variable map see: freemarker.
Now FreeMarker will not print anything to the output when an error occurs, so the control is in your hands. After you have caught the exception of Template. Call httpResp. If the return value was true , then try to finish the page be printing something that makes clear for the visitor that the page generation was abruptly interrupted because of an error on the Web server. Use full page buffering. This means that the Writer doesn't send the output to the client progressively, but buffers the whole page in the memory.
Since you provide the Writer instance for the Template. For example, you may use a StringWriter , and if Template. With this method you surely don't have to deal with partially sent pages, but it can have negative performance implications depending on the characteristic of the pages for example, the user will experience more response delay for a long page that is generated slowly, also the server will consume more RAM.
Note that using a StringWriter is surely not the most efficient solution, as it often reallocates its buffer as the accumulated content grows. Our view is that the editors that break template code are themselves broken. A good editor should ignore, not mangle, what it doesn't understand. You maybe interested in that starting from FreeMarker 2.
For more details read this Last generated: GMT , for Freemarker 2. All other marks mentioned may be trademarks or registered trademarks of their respective owners. Unsupported web browser - Use a modern browser to view this website! Bookmarks: Alpha. Previous Next. JSP versus FreeMarker? Why is FreeMarker so picky about null -s and missing variables, and what to do with it? Why does FreeMarker print the numbers with strange formatting as 1,, or 1 instead of ?
FreeMarker can't find my templates TemplateNotFoundException or FileNotFoundException , "Template not found" error message The documentation writes about feature X , but it seems that FreeMarker doesn't know that, or it behaves in a different way as documented, or a bug that was supposedly fixed is still present.
What to do? What are the legal variable names? How can I use variable names macro name, parameter name that contain minus sign - , colon : , dot. Why do I get "java. How to include other resources in a way as jsp:include does it? Why I can't use non-string key in the myMap[myKey] expression? And what to do now? When I list the contents of a map a hash with? Map methods mixed with the real map entries. Of course, I only want to get the map entries.
How can I modify sequences lists and hashes maps in FreeMarker templates? What about null and the FreeMarker template language? How can I use the output of a directive macro in expressions as a parameter to another directive? Why do I have "? How to retrieve values calculated in templates after template execution done? How to assign to or import into a dynamically constructed variable name like to name that's stored in another variable?
Can I allow users to upload templates and what are the security implications? How to implement a function or macro in Java Language instead of in the template language?
Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Skip to content. Posted By: Anonymous How to handle null values in Freemarker? Solution You can use the?? What does this symbol mean in JavaScript? Inside that, create the following file with name helloworld. When you find yourself copy-pasting common parts between templates a lot, you should probably use macros. Continuing our last example, create a new folder called lib inside the templates directory, and there create a file called utils.
Another way of reusing template fragments is moving the common fragment into its own ftl file. This is less flexible than macros, but simpler in concept: it mimics copy-pasting. FreeMarker requires you to provide an explicit default for variables, so avoid values that are null or undefined:. You can also ask FreeMarker to add? If you need more assistance we offer Online Training and Onsite training as well as consulting. FreeMarker Tutorial.
This tutorial explains how can you define FreeMarker templates and how can you generate output based on these templates. It also demonstrates the usage of macros.
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