Class Encoder
java.lang.Object
java.beans.Encoder
- Direct Known Subclasses:
XMLEncoder
An
Encoder
is a class which can be used to create
files or streams that encode the state of a collection of
JavaBeans in terms of their public APIs. The Encoder
,
in conjunction with its persistence delegates, is responsible for
breaking the object graph down into a series of Statement
s
and Expression
s which can be used to create it.
A subclass typically provides a syntax for these expressions
using some human readable form - like Java source code or XML.- Since:
- 1.4
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Constructor Summary
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Method Summary
Modifier and TypeMethodDescriptionReturns a tentative value foroldInstance
in the environment created by this stream.Gets the exception handler for this stream.getPersistenceDelegate
(Class<?> type) Returns the persistence delegate for the given type.Removes the entry for this instance, returning the old entry.void
setExceptionListener
(ExceptionListener exceptionListener) Sets the exception handler for this stream toexceptionListener
.void
setPersistenceDelegate
(Class<?> type, PersistenceDelegate delegate) Associates the specified persistence delegate with the given type.void
writeExpression
(Expression oldExp) The implementation first checks to see if an expression with this value has already been written.protected void
Write the specified object to the output stream.void
writeStatement
(Statement oldStm) Writes statementoldStm
to the stream.
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Constructor Details
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Encoder
public Encoder()Constructs anEncoder
.
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Method Details
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writeObject
Write the specified object to the output stream. The serialized form will denote a series of expressions, the combined effect of which will create an equivalent object when the input stream is read. By default, the object is assumed to be a JavaBean with a nullary constructor, whose state is defined by the matching pairs of "setter" and "getter" methods returned by the Introspector.- Parameters:
o
- The object to be written to the stream.- See Also:
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setExceptionListener
Sets the exception handler for this stream toexceptionListener
. The exception handler is notified when this stream catches recoverable exceptions.- Parameters:
exceptionListener
- The exception handler for this stream; ifnull
the default exception listener will be used.- See Also:
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getExceptionListener
Gets the exception handler for this stream.- Returns:
- The exception handler for this stream; Will return the default exception listener if this has not explicitly been set.
- See Also:
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getPersistenceDelegate
Returns the persistence delegate for the given type. The persistence delegate is calculated by applying the following rules in order:-
If a persistence delegate is associated with the given type
by using the
setPersistenceDelegate(java.lang.Class<?>, java.beans.PersistenceDelegate)
method it is returned. -
A persistence delegate is then looked up by the name
composed of the fully qualified name of the given type
and the "PersistenceDelegate" postfix.
For example, a persistence delegate for the
Bean
class should be namedBeanPersistenceDelegate
and located in the same package.public class Bean { ... } public class BeanPersistenceDelegate { ... }
The instance of theBeanPersistenceDelegate
class is returned for theBean
class. -
If the type is
null
, a shared internal persistence delegate is returned that encodesnull
value. -
If the type is an
enum
declaration, a shared internal persistence delegate is returned that encodes constants of this enumeration by their names. - If the type is a primitive type or the corresponding wrapper, a shared internal persistence delegate is returned that encodes values of the given type.
- If the type is an array, a shared internal persistence delegate is returned that encodes an array of the appropriate type and length, and each of its elements as if they are properties.
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If the type is a proxy,
a shared internal persistence delegate is returned
that encodes a proxy instance by using
the
Proxy.newProxyInstance(java.lang.ClassLoader, java.lang.Class<?>[], java.lang.reflect.InvocationHandler)
method. -
If the
BeanInfo
for this type has aBeanDescriptor
which defined a "persistenceDelegate" attribute, the value of this named attribute is returned. -
In all other cases the default persistence delegate is returned.
The default persistence delegate assumes the type is a JavaBean,
implying that it has a default constructor and that its state
may be characterized by the matching pairs of "setter" and "getter"
methods returned by the
Introspector
class. The default constructor is the constructor with the greatest number of parameters that has theConstructorProperties
annotation. If none of the constructors has theConstructorProperties
annotation, then the nullary constructor (constructor with no parameters) will be used. For example, in the following code fragment, the nullary constructor for theFoo
class will be used, while the two-parameter constructor for theBar
class will be used.public class Foo { public Foo() { ... } public Foo(int x) { ... } } public class Bar { public Bar() { ... } @ConstructorProperties({"x"}) public Bar(int x) { ... } @ConstructorProperties({"x", "y"}) public Bar(int x, int y) { ... } }
- Parameters:
type
- the class of the objects- Returns:
- the persistence delegate for the given type
- See Also:
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If a persistence delegate is associated with the given type
by using the
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setPersistenceDelegate
Associates the specified persistence delegate with the given type.- Parameters:
type
- the class of objects that the specified persistence delegate applies todelegate
- the persistence delegate for instances of the given type- See Also:
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remove
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get
Returns a tentative value foroldInstance
in the environment created by this stream. A persistence delegate can use itsmutatesTo
method to determine whether this value may be initialized to form the equivalent object at the output or whether a new object must be instantiated afresh. If the stream has not yet seen this value, null is returned.- Parameters:
oldInstance
- The instance to be looked up.- Returns:
- The object, null if the object has not been seen before.
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writeStatement
Writes statementoldStm
to the stream. TheoldStm
should be written entirely in terms of the callers environment, i.e. the target and all arguments should be part of the object graph being written. These expressions represent a series of "what happened" expressions which tell the output stream how to produce an object graph like the original.The implementation of this method will produce a second expression to represent the same expression in an environment that will exist when the stream is read. This is achieved simply by calling
writeObject
on the target and all the arguments and building a new expression with the results.- Parameters:
oldStm
- The expression to be written to the stream.
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writeExpression
The implementation first checks to see if an expression with this value has already been written. If not, the expression is cloned, using the same procedure aswriteStatement
, and the value of this expression is reconciled with the value of the cloned expression by callingwriteObject
.- Parameters:
oldExp
- The expression to be written to the stream.
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