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StrutsParameter Annotation

@StrutsParameter is a security annotation that marks which fields and methods in your Action class can receive values from user requests.

Why it matters: by default (when annotations are required), Struts will only inject request parameters into fields or setter methods that have this annotation. This prevents attackers from setting values on fields you didn’t intend to expose.

Where authorization applies

As of Struts 7.2.0 the @StrutsParameter authorization is enforced across every channel that can populate an action from request data:

ModelDriven actions

When an action implements ModelDriven and the Model Driven Interceptor has pushed the model onto the value stack, the model — not the action — is the authorization target, and the model’s members are exempt from the annotation requirement. The whole model is bindable, including its nested properties, whether or not any of its fields or accessors carry @StrutsParameter.

This follows from what the interface declares: returning an object from getModel() designates that object as the request surface. The model has been the authorization target since Struts 7.0.0.

The exemption holds on every input channel listed above — request parameters, JSON bodies and REST bodies alike — because they all resolve the authorization target the same way. It is not a JSON- or REST-specific behavior.

The exemption is narrowly scoped. It applies only when the action itself implements ModelDriven and the object being populated is its model rather than the action. A root object configured elsewhere — for example the JSON interceptor’s root expression on an action that does not implement ModelDriven — is not exempt, and each member it binds still requires @StrutsParameter.

The exemption lifts the annotation requirement only. The other parameter-name checks — accepted and excluded name patterns, and ParameterNameAware — still apply to a model’s parameters as they do to an action’s.

Because the entire model is bindable, a ModelDriven model should be a request DTO carrying only the fields the action intends to accept from a request, never a domain or persistence entity. If you need member-level control over what is bindable, use action properties annotated with @StrutsParameter rather than ModelDriven.

Usage

The placement of the @StrutsParameter annotation is crucial and depends on how you want to populate your action properties.

Understanding the depth parameter

When you annotate a getter, depth limits how far Struts may traverse the object graph reachable from that getter while applying request parameters. Each navigation step counts as one level — following a property or indexing into a collection or map.

To find the value you need, count the segments after the annotated property in the request expression:

Request expression Annotated getter Steps beyond the getter Required depth
user.name getUser() .name 1
user.address.city getUser() .address → .city 2
users[0].name getUsers() [0] → .name 2

The key point for collections and maps: indexing into the collection is itself a level. Reaching a property of a collection element therefore always costs one more level than reaching the same property on a plain object. This holds even when the element type is a flat POJO with only simple fields — populating contents[0].title still needs depth = 2 (one level to reach the element, one more to reach its property), not depth = 1.

In the annotation’s own terms, depth is the number of periods or brackets that may appear in the parameter name. The default is depth = 0, which permits only setters and fields directly on the action class. Reaching a property of a returned object needs depth = 1 or more; reaching a property of an object held in a collection or map needs depth = 2 or more.

Examples

Simple field

Annotating the field:

public class MyAction {
    @StrutsParameter
    public String username;  // ✅ Can receive request parameter
}

Annotating the setter:

public class MyAction {
    private String username;
    @StrutsParameter
    public void setUsername(String username) {
        this.username = username;
    }
}

Checkbox

For a single checkbox, the annotation must be on the setter.

public class MyAction {
    private boolean myCheckbox;

    @StrutsParameter
    public void setMyCheckbox(boolean myCheckbox) {
        this.myCheckbox = myCheckbox;
    }
    // ... getter
}

Collections

Populating a collection of simple types

When populating a collection of simple types (e.g., from a checkbox list), annotate the setter.

public class MyAction {
    private List<String> mySelection;

    @StrutsParameter
    public void setMySelection(List<String> mySelection) {
        this.mySelection = mySelection;
    }
    // ... getter
}

This covers the case where the whole collection is assigned at once (name mySelection, depth = 0), as a checkbox list submits it.

When the collection is instead populated element by element through indexed names — mySelection[0], mySelection[1] — the annotation must be on the getter with depth = 1, because each element path contains one bracket. This is how JSON and REST payloads bind a collection of simple types: a body such as {"mySelection":["A","B"]} populates mySelection[0] and mySelection[1], so the getter must be annotated for the elements to be accepted.

public class MyAction {
    private List<String> mySelection;

    @StrutsParameter(depth = 1)
    public List<String> getMySelection() {
        return mySelection;
    }
    // ... setter
}

When populating properties of objects that are already in a collection, annotate the getter. Because reaching an element’s property requires indexing into the collection and then following the property, this needs depth = 2 (see Understanding the depth parameter).

public class MyAction {
    private List<User> users; // assume this is initialized in the constructor or elsewhere

    @StrutsParameter(depth = 2)
    public List<User> getUsers() {
        return users;
    }
    // ...
}

This allows requests like users[0].name=John. Note that depth = 2 is required even when User is a flat object with only simple properties — the extra level pays for indexing into the collection, not for nesting within the element.

The same rule applies to JSON and REST payloads: a body such as {"users":[{"name":"John"}]} populates users[0].name, so the getUsers() getter must be annotated with depth = 2 for the nested value to be accepted. Annotating only the setter is not enough — the JSON/REST authorization checks the getter when descending into the collection’s elements.

Complex object

Populating the object itself

To populate the whole object from the request (e.g., using a custom type converter), annotate the setter.

public class MyAction {
    private User user;

    @StrutsParameter
    public void setUser(User user) {
        this.user = user;
    }
    // ... getter
}

Populating properties of a complex object

To populate the properties of a complex object, annotate the getter.

public class MyAction {
    private User user = new User();

    @StrutsParameter(depth = 1)
    public User getUser() {
        return user;
    }
}

This allows requests like user.name=John.

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