Struts源码之ValueStack

/**
* ValueStack allows multiple beans to be pushed in and dynamic EL expressions to be evaluated against it. When
* evaluating an expression, the stack will be searched down the stack, from the latest objects pushed in to the
* earliest, looking for a bean with a getter or setter for the given property or a method of the given name (depending
* on the expression being evaluated).
*/
public interface ValueStack {

public static final String VALUE_STACK = "com.opensymphony.xwork2.util.ValueStack.ValueStack";

public static final String REPORT_ERRORS_ON_NO_PROP = "com.opensymphony.xwork2.util.ValueStack.ReportErrorsOnNoProp";

/**
* Gets the context for this value stack. The context holds all the information in the value stack and it's surroundings.
*
* @return  the context.
*/
public abstract Map<String, Object> getContext();

/**
* Sets the default type to convert to if no type is provided when getting a value.
*
* @param defaultType the new default type
*/
public abstract void setDefaultType(Class defaultType);

/**
* Set a override map containing <code>key -> values</code> that takes precedent when doing find operations on the ValueStack.
* <p/>
* See the unit test for ValueStackTest for examples.
*
* @param overrides  overrides map.
*/
public abstract void setExprOverrides(Map<Object, Object> overrides);

/**
* Gets the override map if anyone exists.
*
* @return the override map, <tt>null</tt> if not set.
*/
public abstract Map<Object, Object> getExprOverrides();

/**
* Get the CompoundRoot which holds the objects pushed onto the stack
*
* @return the root
*/
public abstract CompoundRoot getRoot();

/**
* Attempts to set a property on a bean in the stack with the given expression using the default search order.
*
* @param expr  the expression defining the path to the property to be set.
* @param value the value to be set into the named property
*/
public abstract void setValue(String expr, Object value);

/**
* Attempts to set a property on a bean in the stack with the given expression using the default search order.
* N.B.: unlike #setValue(String,Object) it doesn't allow eval expression.
* @param expr  the expression defining the path to the property to be set.
* @param value the value to be set into the named property
*/
void setParameter(String expr, Object value);

/**
* Attempts to set a property on a bean in the stack with the given expression using the default search order.
*
* @param expr                    the expression defining the path to the property to be set.
* @param value                   the value to be set into the named property
* @param throwExceptionOnFailure a flag to tell whether an exception should be thrown if there is no property with
*                                the given name.
*/
public abstract void setValue(String expr, Object value, boolean throwExceptionOnFailure);

public abstract String findString(String expr);
public abstract String findString(String expr, boolean throwExceptionOnFailure);

/**
* Find a value by evaluating the given expression against the stack in the default search order.
*
* @param expr the expression giving the path of properties to navigate to find the property value to return
* @return the result of evaluating the expression
*/
public abstract Object findValue(String expr);

public abstract Object findValue(String expr, boolean throwExceptionOnFailure);

/**
* Find a value by evaluating the given expression against the stack in the default search order.
*
* @param expr   the expression giving the path of properties to navigate to find the property value to return
* @param asType the type to convert the return value to
* @return the result of evaluating the expression
*/
public abstract Object findValue(String expr, Class asType);
public abstract Object findValue(String expr, Class asType,  boolean throwExceptionOnFailure);

/**
* Get the object on the top of the stack <b>without</b> changing the stack.
*
* @return the object on the top.
* @see CompoundRoot#peek()
*/
public abstract Object peek();

/**
* Get the object on the top of the stack and <b>remove</b> it from the stack.
*
* @return the object on the top of the stack
* @see CompoundRoot#pop()
*/
public abstract Object pop();

/**
* Put this object onto the top of the stack
*
* @param o the object to be pushed onto the stack
* @see CompoundRoot#push(Object)
*/
public abstract void push(Object o);

/**
* Sets an object on the stack with the given key
* so it is retrievable by {@link #findValue(String)}, {@link #findValue(String, Class)}
*
* @param key  the key
* @param o    the object
*/
public abstract void set(String key, Object o);

/**
* Get the number of objects in the stack
*
* @return the number of objects in the stack
*/
public abstract int size();

}