javax.el.ListELResolver Maven / Gradle / Ivy
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package javax.el;
import java.util.List;
import java.util.Iterator;
import java.util.Collections;
import java.util.ArrayList;
import java.beans.FeatureDescriptor;
/**
* Defines property resolution behavior on instances of {@link java.util.List}.
*
* This resolver handles base objects of type java.util.List.
* It accepts any object as a property and coerces that object into an
* integer index into the list. The resulting value is the value in the list
* at that index.
*
* This resolver can be constructed in read-only mode, which means that
* {@link #isReadOnly} will always return true and
* {@link #setValue} will always throw
* PropertyNotWritableException.
*
* ELResolvers are combined together using
* {@link CompositeELResolver}s, to define rich semantics for evaluating
* an expression. See the javadocs for {@link ELResolver} for details.
*
* @see CompositeELResolver
* @see ELResolver
* @see java.util.List
* @since JSP 2.1
*/
public class ListELResolver extends ELResolver {
/**
* Creates a new read/write ListELResolver.
*/
public ListELResolver() {
this.isReadOnly = false;
}
/**
* Creates a new ListELResolver whose read-only status is
* determined by the given parameter.
*
* @param isReadOnly true if this resolver cannot modify
* lists; false otherwise.
*/
public ListELResolver(boolean isReadOnly) {
this.isReadOnly = isReadOnly;
}
/**
* If the base object is a list, returns the most general acceptable type
* for a value in this list.
*
* If the base is a List, the propertyResolved
* property of the ELContext object must be set to
* true by this resolver, before returning. If this property
* is not true after this method is called, the caller
* should ignore the return value.
*
* Assuming the base is a List, this method will always
* return Object.class. This is because Lists
* accept any object as an element.
*
* @param context The context of this evaluation.
* @param base The list to analyze. Only bases of type List
* are handled by this resolver.
* @param property The index of the element in the list to return the
* acceptable type for. Will be coerced into an integer, but
* otherwise ignored by this resolver.
* @return If the propertyResolved property of
* ELContext was set to true, then
* the most general acceptable type; otherwise undefined.
* @throws PropertyNotFoundException if the given index is out of
* bounds for this list.
* @throws NullPointerException if context is null
* @throws ELException if an exception was thrown while performing
* the property or variable resolution. The thrown exception
* must be included as the cause property of this exception, if
* available.
*/
public Class getType(ELContext context,
Object base,
Object property) {
if (context == null) {
throw new NullPointerException();
}
if (base != null && base instanceof List) {
context.setPropertyResolved(true);
List list = (List) base;
int index = toInteger(property);
if (index < 0 || index >= list.size()) {
throw new PropertyNotFoundException();
}
return Object.class;
}
return null;
}
/**
* If the base object is a list, returns the value at the given index.
* The index is specified by the property argument, and
* coerced into an integer. If the coercion could not be performed,
* an IllegalArgumentException is thrown. If the index is
* out of bounds, null is returned.
*
* If the base is a List, the propertyResolved
* property of the ELContext object must be set to
* true by this resolver, before returning. If this property
* is not true after this method is called, the caller
* should ignore the return value.
*
* @param context The context of this evaluation.
* @param base The list to be analyzed. Only bases of type
* List are handled by this resolver.
* @param property The index of the value to be returned. Will be coerced
* into an integer.
* @return If the propertyResolved property of
* ELContext was set to true, then
* the value at the given index or null
* if the index was out of bounds. Otherwise, undefined.
* @throws IllegalArgumentException if the property could not be coerced
* into an integer.
* @throws NullPointerException if context is null.
* @throws ELException if an exception was thrown while performing
* the property or variable resolution. The thrown exception
* must be included as the cause property of this exception, if
* available.
*/
public Object getValue(ELContext context,
Object base,
Object property) {
if (context == null) {
throw new NullPointerException();
}
if (base != null && base instanceof List) {
context.setPropertyResolved(true);
List list = (List) base;
int index = toInteger(property);
if (index < 0 || index >= list.size()) {
return null;
}
return list.get(index);
}
return null;
}
/**
* If the base object is a list, attempts to set the value at the
* given index with the given value. The index is specified by the
* property argument, and coerced into an integer. If the
* coercion could not be performed, an
* IllegalArgumentException is thrown. If the index is
* out of bounds, a PropertyNotFoundException is thrown.
*
* If the base is a List, the propertyResolved
* property of the ELContext object must be set to
* true by this resolver, before returning. If this property
* is not true after this method is called, the caller
* can safely assume no value was set.
*
* If this resolver was constructed in read-only mode, this method will
* always throw PropertyNotWritableException.
*
* If a List was created using
* {@link java.util.Collections#unmodifiableList}, this method must
* throw PropertyNotWritableException. Unfortunately,
* there is no Collections API method to detect this. However, an
* implementation can create a prototype unmodifiable List
* and query its runtime type to see if it matches the runtime type of
* the base object as a workaround.
*
* @param context The context of this evaluation.
* @param base The list to be modified. Only bases of type
* List are handled by this resolver.
* @param property The index of the value to be set. Will be coerced
* into an integer.
* @param val The value to be set at the given index.
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list.
* @throws NullPointerException if context is null, or
* if the value is null and this List
* does not support null elements.
* @throws IllegalArgumentException if the property could not be coerced
* into an integer, or if some aspect of the specified element
* prevents it from being added to this list.
* @throws PropertyNotWritableException if this resolver was constructed
* in read-only mode, or if the set operation is not supported by
* the underlying list.
* @throws PropertyNotFoundException if the given index is out of
* bounds for this list.
* @throws ELException if an exception was thrown while performing
* the property or variable resolution. The thrown exception
* must be included as the cause property of this exception, if
* available.
*/
public void setValue(ELContext context,
Object base,
Object property,
Object val) {
if (context == null) {
throw new NullPointerException();
}
if (base != null && base instanceof List) {
context.setPropertyResolved(true);
List list = (List) base;
int index = toInteger(property);
if (isReadOnly) {
throw new PropertyNotWritableException();
}
try {
list.set(index, val);
} catch (UnsupportedOperationException ex) {
throw new PropertyNotWritableException();
} catch (IndexOutOfBoundsException ex) {
throw new PropertyNotFoundException();
} catch (ClassCastException ex) {
throw ex;
} catch (NullPointerException ex) {
throw ex;
} catch (IllegalArgumentException ex) {
throw ex;
}
}
}
static private Class theUnmodifiableListClass =
Collections.unmodifiableList(new ArrayList()).getClass();
/**
* If the base object is a list, returns whether a call to
* {@link #setValue} will always fail.
*
* If the base is a List, the propertyResolved
* property of the ELContext object must be set to
* true by this resolver, before returning. If this property
* is not true after this method is called, the caller
* should ignore the return value.
*
* If this resolver was constructed in read-only mode, this method will
* always return true.
*
* If a List was created using
* {@link java.util.Collections#unmodifiableList}, this method must
* return true. Unfortunately, there is no Collections API
* method to detect this. However, an implementation can create a
* prototype unmodifiable List and query its runtime type
* to see if it matches the runtime type of the base object as a
* workaround.
*
* @param context The context of this evaluation.
* @param base The list to analyze. Only bases of type List
* are handled by this resolver.
* @param property The index of the element in the list to return the
* acceptable type for. Will be coerced into an integer, but
* otherwise ignored by this resolver.
* @return If the propertyResolved property of
* ELContext was set to true, then
* true if calling the setValue method
* will always fail or false if it is possible that
* such a call may succeed; otherwise undefined.
* @throws PropertyNotFoundException if the given index is out of
* bounds for this list.
* @throws NullPointerException if context is null
* @throws ELException if an exception was thrown while performing
* the property or variable resolution. The thrown exception
* must be included as the cause property of this exception, if
* available.
*/
public boolean isReadOnly(ELContext context,
Object base,
Object property) {
if (context == null) {
throw new NullPointerException();
}
if (base != null && base instanceof List) {
context.setPropertyResolved(true);
List list = (List) base;
int index = toInteger(property);
if (index < 0 || index >= list.size()) {
throw new PropertyNotFoundException();
}
return list.getClass() == theUnmodifiableListClass || isReadOnly;
}
return false;
}
/**
* Always returns null, since there is no reason to
* iterate through set set of all integers.
*
* The {@link #getCommonPropertyType} method returns sufficient
* information about what properties this resolver accepts.
*
* @param context The context of this evaluation.
* @param base The list. Only bases of type List are
* handled by this resolver.
* @return null.
*/
public Iterator getFeatureDescriptors(
ELContext context,
Object base) {
return null;
}
/**
* If the base object is a list, returns the most general type that
* this resolver accepts for the property argument.
* Otherwise, returns null.
*
* Assuming the base is a List, this method will always
* return Integer.class. This is because Lists
* accept integers as their index.
*
* @param context The context of this evaluation.
* @param base The list to analyze. Only bases of type List
* are handled by this resolver.
* @return null if base is not a List; otherwise
* Integer.class.
*/
public Class getCommonPropertyType(ELContext context,
Object base) {
if (base != null && base instanceof List) {
return Integer.class;
}
return null;
}
private int toInteger(Object p) {
if (p instanceof Integer) {
return ((Integer) p).intValue();
}
if (p instanceof Character) {
return ((Character) p).charValue();
}
if (p instanceof Boolean) {
return ((Boolean) p).booleanValue()? 1: 0;
}
if (p instanceof Number) {
return ((Number) p).intValue();
}
if (p instanceof String) {
return Integer.parseInt((String) p);
}
throw new IllegalArgumentException();
}
private boolean isReadOnly;
}