org.apache.el: public final class: ValueExpressionImpl

org.apache.el
public final class: ValueExpressionImpl [javadoc | source]

java.lang.Object
   javax.el.ValueExpression
      org.apache.el.ValueExpressionImpl

All Implemented Interfaces:
Externalizable

An Expression that can get or set a value.

In previous incarnations of this API, expressions could only be read. ValueExpression objects can now be used both to retrieve a value and to set a value. Expressions that can have a value set on them are referred to as l-value expressions. Those that cannot are referred to as r-value expressions. Not all r-value expressions can be used as l-value expressions (e.g. "${1+1}" or "${firstName} ${lastName}"). See the EL Specification for details. Expressions that cannot be used as l-values must always return true from isReadOnly().

The ExpressionFactory#createValueExpression method can be used to parse an expression string and return a concrete instance of ValueExpression 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 #getValue , #setValue , #isReadOnly  and
#getType  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 four methods,
the ELResolver#getValue  method is used to resolve all properties
up to but excluding the last one. This provides the base
object. At the last resolution, the ValueExpression will
call the corresponding ELResolver#getValue ,
ELResolver#setValue , ELResolver#isReadOnly  or
ELResolver#getType  method, depending on which was called on
the ValueExpression.


See the notes about comparison, serialization and immutability in
the Expression  javadocs.
Also see:
javax.el.ELResolver
javax.el.Expression
javax.el.ExpressionFactory
javax.el.ValueExpression
author: Jacob -  Hookom [jacob@hookom.net]
version: $ - Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: markt $









    







    












    Constructor:
 public ValueExpressionImpl() {

}
 public ValueExpressionImpl(String expr,
    Node node,
    FunctionMapper fnMapper,
    VariableMapper varMapper,
    Class expectedType) {
        this.expr = expr;
        this.node = node;
        this.fnMapper = fnMapper;
        this.varMapper = varMapper;
        this.expectedType = expectedType;
}











    Method from org.apache.el.ValueExpressionImpl Summary:

equals,   getExpectedType,   getExpressionString,   getType,   getValue,   hashCode,   isLiteralText,   isReadOnly,   readExternal,   setValue,   toString,   writeExternal
Methods from java.lang.Object:

equals,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from org.apache.el.ValueExpressionImpl Detail:
 public boolean equals(Object obj) {
        return (obj instanceof ValueExpressionImpl && obj.hashCode() == this
                .hashCode());
}
 public Class getExpectedType() {
        return this.expectedType;
}
 public String getExpressionString() {
        return this.expr;
}
Returns the type the result of the expression will be coerced to after
evaluation.
 public Class getType(ELContext context) throws PropertyNotFoundException, ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        return this.getNode().getType(ctx);
}
 public Object getValue(ELContext context) throws PropertyNotFoundException, ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        Object value = this.getNode().getValue(ctx);
        if (this.expectedType != null) {
            return ELSupport.coerceToType(value, this.expectedType);
        }
        return value;
}
 public int hashCode() {
        return this.expr.hashCode();
}
 public boolean isLiteralText() {
        try {
            return this.getNode() instanceof AstLiteralExpression;
        } catch (ELException ele) {
            return false;
        }
}
 public boolean isReadOnly(ELContext context) throws PropertyNotFoundException, ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        return this.getNode().isReadOnly(ctx);
}
 public  void readExternal(ObjectInput in) throws ClassNotFoundException, IOException {
        this.expr = in.readUTF();
        String type = in.readUTF();
        if (!"".equals(type)) {
            this.expectedType = ReflectionUtil.forName(type);
        }
        this.fnMapper = (FunctionMapper) in.readObject();
        this.varMapper = (VariableMapper) in.readObject();
}
 public  void setValue(ELContext context,
    Object value) throws PropertyNotWritableException, PropertyNotFoundException, ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        this.getNode().setValue(ctx, value);
}
 public String toString() {
        return "ValueExpression["+this.expr+"]";
}
 public  void writeExternal(ObjectOutput out) throws IOException {
        out.writeUTF(this.expr);
        out.writeUTF((this.expectedType != null) ? this.expectedType.getName()
                : "");
        out.writeObject(this.fnMapper);
        out.writeObject(this.varMapper);
}