Class Accessor
The Accessor uses a dot notation such as field1.method1.method2 to perform the access on an object. Each value in the notation refers to a field or method (a no argument method) of the type of the previous value. For instance if you have the following class structure:
public class A { public B = new B (); } public class B { public C = new C (); } public class C { String d = ""; }
You would then use the notation: B.C.d to get access to
field d in Class C.
The Accessor also supports a [ ] notation for accessing
into Lists/Maps and Arrays. If the value between the [ ]
is an integer then we look for the associated type to be either
an array or a List, we then index into it with the integer. If
the value is NOT an integer then we use assume the
type is a Map and use it as a key into the Map.
For instance changing the example above:
public class A { public List vals = new ArrayList (); }
Now we could use: vals[X] where X is a positive integer. Or changing again:
public class A { public Map vals = new HashMap (); }
We could use: vals[VALUE] where VALUE would then be
used as a Key into the vals HashMap.
Note: The Accessor is NOT designed to be an all purpose
method of gaining access to a class. It has specific uses and for
most will be of no use at all. It should be used for general purpose
applications where you want to access specific fields of an object
without having to know the exact type. One such application is in
the GeneralComparator
, in that case arbitrary Objects can
be sorted without having to write complex Comparators or implementing
the Comparable interface AND it gives the flexibility that sorting
can be changed ad-hoc.
The Accessor looks for in the following order:
- Public fields with the specified name.
- If no field is found then the name is converted to a "JavaBeans" get method, so a field name of value would be converted to getValue and that method is looked for. The method must take no arguments.
- If we don't find the get* method then we look for a method with the specified name. So a field name of value would mean that a method (that again takes no arguments) is looked for.
Note: we have had to add the 3rd type to allow for methods that don't follow JavaBeans conventions (there are loads in the standard Java APIs which makes accessing impossible otherwise).
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionstatic List
getAccessorChain
(String accessorRef, Class clazz) Get the Java field associated with the named field.getIndex()
static Object
getValueForIndex
(Object data, String index) static Object
getValueFromAccessorChain
(Object obj, List chain) boolean
void
setAccessor
(Field f) void
void
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Constructor Details
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Accessor
public Accessor()
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Method Details
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getIndex
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setIndex
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setAccessor
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setAccessor
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isIndexCorrectForType
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getValueFromAccessorChain
public static Object getValueFromAccessorChain(Object obj, List chain) throws IllegalAccessException, InvocationTargetException -
getValueForIndex
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getAccessorChain
public static List getAccessorChain(String accessorRef, Class clazz) throws IllegalArgumentException Get the Java field associated with the named field. Return null if there isn't one, or if we can't access it.- Parameters:
clazz
- The Class to get the field from.field
- The name of the field.- Returns:
- A List of Accessor objects used for delving into the classes to be sorted.
- Throws:
IllegalArgumentException
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