javax.el: public class: CompositeELResolver

javax.el
public class: CompositeELResolver [javadoc | source]

java.lang.Object
   javax.el.ELResolver
      javax.el.CompositeELResolver

Maintains an ordered composite list of child ELResolvers.

Though only a single ELResolver is associated with an ELContext, there are usually multiple resolvers considered for any given variable or property resolution. ELResolvers are combined together using a CompositeELResolver, to define rich semantics for evaluating an expression.

For the #getValue , #getType , #setValue and #isReadOnly methods, an ELResolver is not responsible for resolving all possible (base, property) pairs. In fact, most resolvers will only handle a base of a single type. To indicate that a resolver has successfully resolved a particular (base, property) pair, it must set the propertyResolved property of the ELContext to true. If it could not handle the given pair, it must leave this property alone. The caller must ignore the return value of the method if propertyResolved is false.

The CompositeELResolver initializes the ELContext.propertyResolved flag to false, and uses it as a stop condition for iterating through its component resolvers.

The ELContext.propertyResolved flag is not used for the design-time methods #getFeatureDescriptors and #getCommonPropertyType . Instead, results are collected and combined from all child ELResolvers for these methods.

Also see:

ELContext

ELResolver

since: JSP - 2.1

Fields inherited from javax.el.ELResolver:
TYPE, RESOLVABLE_AT_DESIGN_TIME

Method from javax.el.CompositeELResolver Summary:
add, getCommonPropertyType, getFeatureDescriptors, getType, getValue, isReadOnly, setValue

Methods from javax.el.ELResolver:
getCommonPropertyType, getFeatureDescriptors, getType, getValue, isReadOnly, setValue

Methods from java.lang.Object:
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from javax.el.CompositeELResolver Detail:
public void add(ELResolver elResolver) { if (elResolver == null) { throw new NullPointerException(); } elResolvers.add(elResolver); } Adds the given resolver to the list of component resolvers. Resolvers are consulted in the order in which they are added.
public Class getCommonPropertyType(ELContext context, Object base) { Class< ? > commonPropertyType = null; Iterator< ELResolver > iter = elResolvers.iterator(); while (iter.hasNext()) { ELResolver elResolver = iter.next(); Class< ? > type = elResolver.getCommonPropertyType(context, base); if (type == null) { // skip this EL Resolver continue; } else if (commonPropertyType == null) { commonPropertyType = type; } else if (commonPropertyType.isAssignableFrom(type)) { continue; } else if (type.isAssignableFrom(commonPropertyType)) { commonPropertyType = type; } else { // Don't have a commonPropertyType return null; } } return commonPropertyType; } Returns the most general type that this resolver accepts for the `property` argument, given a `base` object. One use for this method is to assist tools in auto-completion. The result is obtained by querying all component resolvers. The `Class` returned is the most specific class that is a common superclass of all the classes returned by each component resolver's `getCommonPropertyType` method. If `null` is returned by a resolver, it is skipped.
public Iterator getFeatureDescriptors(ELContext context, Object base) { return new CompositeIterator(elResolvers.iterator(), context, base); } Returns information about the set of variables or properties that can be resolved for the given `base` object. One use for this method is to assist tools in auto-completion. The results are collected from all component resolvers. The `propertyResolved` property of the `ELContext` is not relevant to this method. The results of all `ELResolver`s are concatenated. The `Iterator` returned is an iterator over the collection of `FeatureDescriptor` objects returned by the iterators returned by each component resolver's `getFeatureDescriptors` method. If `null` is returned by a resolver, it is skipped.
public Class getType(ELContext context, Object base, Object property) { context.setPropertyResolved(false); int i = 0, len = this.elResolvers.size(); ELResolver elResolver; Class< ? > type; while (i < len) { elResolver = this.elResolvers.get(i); type = elResolver.getType(context, base, property); if (context.isPropertyResolved()) { return type; } i++; } return null; } For a given `base` and `property`, attempts to identify the most general type that is acceptable for an object to be passed as the `value` parameter in a future call to the #setValue method. The result is obtained by querying all component resolvers. If this resolver handles the given (base, property) pair, the `propertyResolved` property of the `ELContext` object must be set to `true` by the resolver, before returning. If this property is not `true` after this method is called, the caller should ignore the return value. First, `propertyResolved` is set to `false` on the provided `ELContext`. Next, for each component resolver in this composite: The `getType()` method is called, passing in the provided `context`, `base` and `property`. If the `ELContext`'s `propertyResolved` flag is `false` then iteration continues. Otherwise, iteration stops and no more component resolvers are considered. The value returned by `getType()` is returned by this method. If none of the component resolvers were able to perform this operation, the value `null` is returned and the `propertyResolved` flag remains set to `false` . Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
public Object getValue(ELContext context, Object base, Object property) { context.setPropertyResolved(false); int i = 0, len = this.elResolvers.size(); ELResolver elResolver; Object value; while (i < len) { elResolver = this.elResolvers.get(i); value = elResolver.getValue(context, base, property); if (context.isPropertyResolved()) { return value; } i++; } return null; } Attempts to resolve the given `property` object on the given `base` object by querying all component resolvers. If this resolver handles the given (base, property) pair, the `propertyResolved` property of the `ELContext` object must be set to `true` by the resolver, before returning. If this property is not `true` after this method is called, the caller should ignore the return value. First, `propertyResolved` is set to `false` on the provided `ELContext`. Next, for each component resolver in this composite: The `getValue()` method is called, passing in the provided `context`, `base` and `property`. If the `ELContext`'s `propertyResolved` flag is `false` then iteration continues. Otherwise, iteration stops and no more component resolvers are considered. The value returned by `getValue()` is returned by this method. If none of the component resolvers were able to perform this operation, the value `null` is returned and the `propertyResolved` flag remains set to `false` . Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
public boolean isReadOnly(ELContext context, Object base, Object property) { context.setPropertyResolved(false); int i = 0, len = this.elResolvers.size(); ELResolver elResolver; boolean readOnly; while (i < len) { elResolver = this.elResolvers.get(i); readOnly = elResolver.isReadOnly(context, base, property); if (context.isPropertyResolved()) { return readOnly; } i++; } return false; // Does not matter } For a given `base` and `property`, attempts to determine whether a call to #setValue will always fail. The result is obtained by querying all component resolvers. If this resolver handles the given (base, property) pair, the `propertyResolved` property of the `ELContext` object must be set to `true` by the resolver, before returning. If this property is not `true` after this method is called, the caller should ignore the return value. First, `propertyResolved` is set to `false` on the provided `ELContext`. Next, for each component resolver in this composite: The `isReadOnly()` method is called, passing in the provided `context`, `base` and `property`. If the `ELContext`'s `propertyResolved` flag is `false` then iteration continues. Otherwise, iteration stops and no more component resolvers are considered. The value returned by `isReadOnly()` is returned by this method. If none of the component resolvers were able to perform this operation, the value `false` is returned and the `propertyResolved` flag remains set to `false` . Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
public void setValue(ELContext context, Object base, Object property, Object val) { context.setPropertyResolved(false); int i = 0, len = this.elResolvers.size(); ELResolver elResolver; while (i < len) { elResolver = this.elResolvers.get(i); elResolver.setValue(context, base, property, val); if (context.isPropertyResolved()) { return; } i++; } } Attempts to set the value of the given `property` object on the given `base` object. All component resolvers are asked to attempt to set the value. If this resolver handles the given (base, property) pair, the `propertyResolved` property of the `ELContext` object must be set to `true` by the resolver, before returning. If this property is not `true` after this method is called, the caller can safely assume no value has been set. First, `propertyResolved` is set to `false` on the provided `ELContext`. Next, for each component resolver in this composite: The `setValue()` method is called, passing in the provided `context`, `base`, `property` and `value`. If the `ELContext`'s `propertyResolved` flag is `false` then iteration continues. Otherwise, iteration stops and no more component resolvers are considered. If none of the component resolvers were able to perform this operation, the `propertyResolved` flag remains set to `false` . Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.

Method from javax.el.CompositeELResolver Detail:

 public  void add(ELResolver elResolver) {
        if (elResolver == null) {
            throw new NullPointerException();
        }
        elResolvers.add(elResolver);
}

Resolvers are consulted in the order in which they are added.

 public Class getCommonPropertyType(ELContext context,
    Object base) {
        Class< ? > commonPropertyType = null;
        Iterator< ELResolver > iter = elResolvers.iterator();
        while (iter.hasNext()) {
            ELResolver elResolver = iter.next();
            Class< ? > type = elResolver.getCommonPropertyType(context, base);
            if (type == null) {
                // skip this EL Resolver
                continue;
            } else if (commonPropertyType == null) {
                commonPropertyType = type;
            } else if (commonPropertyType.isAssignableFrom(type)) {
                continue;
            } else if (type.isAssignableFrom(commonPropertyType)) {
                commonPropertyType = type;
            } else {
                // Don't have a commonPropertyType
                return null;
            }
        }
        return commonPropertyType;
}

property

base

The Class returned is the most specific class that is a common superclass of all the classes returned by each component resolver's getCommonPropertyType method. If null is returned by a resolver, it is skipped.

 public Iterator getFeatureDescriptors(ELContext context,
    Object base) {
        return new CompositeIterator(elResolvers.iterator(), context, base);
}

base

The propertyResolved property of the ELContext is not relevant to this method. The results of all ELResolvers are concatenated.

The Iterator returned is an iterator over the collection of FeatureDescriptor objects returned by the iterators returned by each component resolver's getFeatureDescriptors method. If null is returned by a resolver, it is skipped.

 public Class getType(ELContext context,
    Object base,
    Object property) {
        context.setPropertyResolved(false);
        int i = 0, len = this.elResolvers.size();
        ELResolver elResolver;
        Class< ? > type;  
        while (i <  len) {
            elResolver = this.elResolvers.get(i);
            type = elResolver.getType(context, base, property);
            if (context.isPropertyResolved()) {
                return type;
            }
            i++;
        }
        return null;
}

base

property

value

#setValue

If this resolver handles the given (base, property) pair, the propertyResolved property of the ELContext object must be set to true by the resolver, before returning. If this property is not true after this method is called, the caller should ignore the return value.

First, propertyResolved is set to false on the provided ELContext.

Next, for each component resolver in this composite:

The getType() method is called, passing in the provided context, base and property.
If the ELContext's propertyResolved flag is false then iteration continues.
Otherwise, iteration stops and no more component resolvers are considered. The value returned by getType() is returned by this method.

If none of the component resolvers were able to perform this operation, the value null is returned and the propertyResolved flag remains set to false

Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.

 public Object getValue(ELContext context,
    Object base,
    Object property) {
        context.setPropertyResolved(false);
        int i = 0, len = this.elResolvers.size();
        ELResolver elResolver;
        Object value; 
        while (i <  len) {
            elResolver = this.elResolvers.get(i);
            value = elResolver.getValue(context, base, property);
            if (context.isPropertyResolved()) {
                return value;
            }
            i++;
        } 
        return null;
}

property

base

First, propertyResolved is set to false on the provided ELContext.

Next, for each component resolver in this composite:

The getValue() method is called, passing in the provided context, base and property.
If the ELContext's propertyResolved flag is false then iteration continues.
Otherwise, iteration stops and no more component resolvers are considered. The value returned by getValue() is returned by this method.

If none of the component resolvers were able to perform this operation, the value null is returned and the propertyResolved flag remains set to false

Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.

 public boolean isReadOnly(ELContext context,
    Object base,
    Object property) {
        context.setPropertyResolved(false);
        int i = 0, len = this.elResolvers.size();
        ELResolver elResolver;
        boolean readOnly;
        while (i <  len) {
            elResolver = this.elResolvers.get(i);
            readOnly = elResolver.isReadOnly(context, base, property);
            if (context.isPropertyResolved()) {
                return readOnly;
            }
            i++;
        }
        return false; // Does not matter
}

base

property

#setValue

First, propertyResolved is set to false on the provided ELContext.

Next, for each component resolver in this composite:

The isReadOnly() method is called, passing in the provided context, base and property.
If the ELContext's propertyResolved flag is false then iteration continues.
Otherwise, iteration stops and no more component resolvers are considered. The value returned by isReadOnly() is returned by this method.

If none of the component resolvers were able to perform this operation, the value false is returned and the propertyResolved flag remains set to false

Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.

 public  void setValue(ELContext context,
    Object base,
    Object property,
    Object val) {
        context.setPropertyResolved(false);
        int i = 0, len = this.elResolvers.size();
        ELResolver elResolver;
        while (i <  len) {
            elResolver = this.elResolvers.get(i);
            elResolver.setValue(context, base, property, val);
            if (context.isPropertyResolved()) {
                return;
            }
            i++;
        }
}

property

base

First, propertyResolved is set to false on the provided ELContext.

Next, for each component resolver in this composite:

The setValue() method is called, passing in the provided context, base, property and value.
If the ELContext's propertyResolved flag is false then iteration continues.
Otherwise, iteration stops and no more component resolvers are considered.

If none of the component resolvers were able to perform this operation, the propertyResolved flag remains set to false

Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.