org.apache.el

Class MethodExpressionImpl

java.lang.Object

javax.el.Expression

javax.el.MethodExpression

org.apache.el.MethodExpressionImpl

All Implemented Interfaces:

Externalizable, Serializable

public final class MethodExpressionImpl
extends MethodExpression
implements Externalizable

An Expression that refers to a method on an object.

The ExpressionFactory.createMethodExpression(javax.el.ELContext, java.lang.String, java.lang.Class<?>, java.lang.Class<?>[]) method can be used to parse an expression string and return a concrete instance of MethodExpression that encapsulates the parsed expression. The FunctionMapper is used at parse time, not evaluation time, so one is not needed to evaluate an expression using this class. However, the ELContext is needed at evaluation time.

The getMethodInfo(javax.el.ELContext) and invoke(javax.el.ELContext, java.lang.Object[]) methods will evaluate the expression each time they are called. The ELResolver in the ELContext is used to resolve the top-level variables and to determine the behavior of the . and [] operators. For any of the two methods, the ELResolver.getValue(javax.el.ELContext, java.lang.Object, java.lang.Object) method is used to resolve all properties up to but excluding the last one. This provides the base object on which the method appears. If the base object is null, a NullPointerException must be thrown. At the last resolution, the final property is then coerced to a String, which provides the name of the method to be found. A method matching the name and expected parameters provided at parse time is found and it is either queried or invoked (depending on the method called on this MethodExpression).

See the notes about comparison, serialization and immutability in the Expression javadocs.

Author:

Jacob Hookom [jacob@hookom.net]

See Also:

ELResolver, Expression, ExpressionFactory, MethodExpression, Serialized Form

Constructor Summary

Constructors

Constructor and Description
MethodExpressionImpl()
MethodExpressionImpl(String expr, Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class<?> expectedType, Class<?>[] paramTypes)

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(Object obj) Determines whether the specified object is equal to this Expression.
String	getExpressionString() Returns the original String used to create this Expression, unmodified.
MethodInfo	getMethodInfo(ELContext context) Evaluates the expression relative to the provided context, and returns information about the actual referenced method.
int	hashCode() Returns the hash code for this Expression.
Object	invoke(ELContext context, Object[] params) Evaluates the expression relative to the provided context, invokes the method that was found using the supplied parameters, and returns the result of the method invocation.
boolean	isLiteralText()
boolean	isParametersProvided()
boolean	isParmetersProvided()
void	readExternal(ObjectInput in)
void	writeExternal(ObjectOutput out)

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MethodExpressionImpl

public MethodExpressionImpl()

MethodExpressionImpl

public MethodExpressionImpl(String expr,
                    Node node,
                    FunctionMapper fnMapper,
                    VariableMapper varMapper,
                    Class<?> expectedType,
                    Class<?>[] paramTypes)

Method Detail

equals

public boolean equals(Object obj)

Determines whether the specified object is equal to this Expression.

The result is true if and only if the argument is not null, is an Expression object that is the of the same type (ValueExpression or MethodExpression), and has an identical parsed representation.

Note that two expressions can be equal if their expression Strings are different. For example, ${fn1:foo()} and ${fn2:foo()} are equal if their corresponding FunctionMappers mapped fn1:foo and fn2:foo to the same method.

Specified by:

equals in class Expression

Parameters:

obj - the Object to test for equality.

Returns:

true if obj equals this Expression; false otherwise.

See Also:

Hashtable, Object.equals(java.lang.Object)

getExpressionString

public String getExpressionString()

Returns the original String used to create this Expression, unmodified.

This is used for debugging purposes but also for the purposes of comparison (e.g. to ensure the expression in a configuration file has not changed).

This method does not provide sufficient information to re-create an expression. Two different expressions can have exactly the same expression string but different function mappings. Serialization should be used to save and restore the state of an Expression.

Specified by:

getExpressionString in class Expression

Returns:

The original expression String.

See Also:

Expression.getExpressionString()

getMethodInfo

public MethodInfo getMethodInfo(ELContext context)
                         throws PropertyNotFoundException,
                                MethodNotFoundException,
                                ELException

Evaluates the expression relative to the provided context, and returns information about the actual referenced method.

Specified by:

getMethodInfo in class MethodExpression

Parameters:

context - The context of this evaluation

Returns:

an instance of MethodInfo containing information about the method the expression evaluated to.

Throws:

NullPointerException - if context is null or the base object is null on the last resolution.

PropertyNotFoundException - if one of the property resolutions failed because a specified variable or property does not exist or is not readable.

MethodNotFoundException - if no suitable method can be found.

ELException - if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

See Also:

MethodExpression.getMethodInfo(javax.el.ELContext)

hashCode

public int hashCode()

Returns the hash code for this Expression.

See the note in the equals(java.lang.Object) method on how two expressions can be equal if their expression Strings are different. Recall that if two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. Implementations must take special note and implement hashCode correctly.

Specified by:

hashCode in class Expression

Returns:

The hash code for this Expression.

See Also:

equals(java.lang.Object), Hashtable, Object.hashCode()

invoke

public Object invoke(ELContext context,
            Object[] params)
              throws PropertyNotFoundException,
                     MethodNotFoundException,
                     ELException

Evaluates the expression relative to the provided context, invokes the method that was found using the supplied parameters, and returns the result of the method invocation.

Specified by:

invoke in class MethodExpression

Parameters:

context - The context of this evaluation.

params - The parameters to pass to the method, or null if no parameters.

Returns:

the result of the method invocation (null if the method has a void return type).

Throws:

NullPointerException - if context is null or the base object is null on the last resolution.

PropertyNotFoundException - if one of the property resolutions failed because a specified variable or property does not exist or is not readable.

MethodNotFoundException - if no suitable method can be found.

ELException - if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available. If the exception thrown is an InvocationTargetException, extract its cause and pass it to the ELException constructor.

See Also:

MethodExpression.invoke(javax.el.ELContext, java.lang.Object[])

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
                         ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Throws:

IOException

ClassNotFoundException

writeExternal

public void writeExternal(ObjectOutput out)
                   throws IOException

Specified by:

writeExternal in interface Externalizable

Throws:

IOException

isLiteralText

public boolean isLiteralText()

Specified by:

isLiteralText in class Expression

isParametersProvided

public boolean isParametersProvided()

Overrides:

isParametersProvided in class MethodExpression

Returns:

This default implementation always returns false

Since:

EL 3.0

isParmetersProvided

public boolean isParmetersProvided()

Overrides:

isParmetersProvided in class MethodExpression

Returns:

Always false

Since:

EL 2.2 Note: The spelling mistake is deliberate. isParmetersProvided() - Specification definition isParametersProvided() - Corrected spelling