Annotation Type MXBean
@Documented @Retention(RUNTIME) @Target(TYPE) public @interface MXBean
Annotation to mark an interface explicitly as being an MXBean interface, or as not being an MXBean interface. By default, an interface is an MXBean interface if it is public and its name ends with MXBean
, as in SomethingMXBean
. The following interfaces are MXBean interfaces:
public interface WhatsitMXBean {} @MXBean public interface Whatsit1Interface {} @MXBean(true) public interface Whatsit2Interface {}
The following interfaces are not MXBean interfaces:
interface NonPublicInterfaceNotMXBean{} public interface Whatsit3Interface{} @MXBean(false) public interface MisleadingMXBean {}
MXBean specification
The MXBean concept provides a simple way to code an MBean that only references a predefined set of types, the ones defined by javax.management.openmbean
. In this way, you can be sure that your MBean will be usable by any client, including remote clients, without any requirement that the client have access to model-specific classes representing the types of your MBeans.
The concepts are easier to understand by comparison with the Standard MBean concept. Here is how a managed object might be represented as a Standard MBean, and as an MXBean:
Standard MBean
public interface MemoryPoolMBean { String getName(); MemoryUsage getUsage(); // ... }
MXBean
public interface MemoryPoolMXBean { String getName(); MemoryUsage getUsage(); // ... }
As you can see, the definitions are very similar. The only difference is that the convention for naming the interface is to use SomethingMXBean
for MXBeans, rather than SomethingMBean
for Standard MBeans.
In this managed object, there is an attribute called Usage
of type MemoryUsage
. The point of an attribute like this is that it gives a coherent snapshot of a set of data items. For example, it might include the current amount of used memory in the memory pool, and the current maximum of the memory pool. If these were separate items, obtained with separate getAttribute
calls, then we could get values seen at different times that were not consistent. We might get a used
value that was greater than the max
value.
So, we might define MemoryUsage
like this:
Standard MBean
public class MemoryUsage implements Serializable { // standard JavaBean conventions with getters public MemoryUsage(long init, long used, long committed, long max) {...} long getInit() {...} long getUsed() {...} long getCommitted() {...} long getMax() {...} }
MXBean
public class MemoryUsage { // standard JavaBean conventions with getters @ConstructorParameters({"init", "used", "committed", "max"}) public MemoryUsage(long init, long used, long committed, long max) {...} long getInit() {...} long getUsed() {...} long getCommitted() {...} long getMax() {...} }
The definitions are the same in the two cases, except that with the MXBean, MemoryUsage
no longer needs to be marked Serializable
(though it can be). On the other hand, we have added a @ConstructorParameters
annotation to link the constructor parameters to the corresponding getters. We will see more about this below.
MemoryUsage
is a model-specific class. With Standard MBeans, a client of the MBean Server cannot access the Usage
attribute if it does not know the class MemoryUsage
. Suppose the client is a generic console based on JMX technology. Then the console would have to be configured with the model-specific classes of every application it might connect to. The problem is even worse for clients that are not written in the Java language. Then there may not be any way to tell the client what a MemoryUsage
looks like.
This is where MXBeans differ from Standard MBeans. Although we define the management interface in almost exactly the same way, the MXBean framework converts model-specific classes into standard classes from the Java platform. Using arrays and the CompositeData
and TabularData
classes from the standard javax.management.openmbean
package, it is possible to build data structures of arbitrary complexity using only standard classes.
This becomes clearer if we compare what the clients of the two models might look like:
Standard MBean
String name = (String) mbeanServer.getAttribute(objectName, "Name"); MemoryUsage usage = (MemoryUsage) mbeanServer.getAttribute(objectName, "Usage"); long used = usage.getUsed();
MXBean
String name = (String) mbeanServer.getAttribute(objectName, "Name"); CompositeData usage = (CompositeData) mbeanServer.getAttribute(objectName, "Usage"); long used = (Long) usage.get("used");
For attributes with simple types like String
, the code is the same. But for attributes with complex types, the Standard MBean code requires the client to know the model-specific class MemoryUsage
, while the MXBean code requires no non-standard classes.
The client code shown here is slightly more complicated for the MXBean client. But, if the client does in fact know the model, here the interface MemoryPoolMXBean
and the class MemoryUsage
, then it can construct a proxy. This is the recommended way to interact with managed objects when you know the model beforehand, regardless of whether you are using Standard MBeans or MXBeans:
Standard MBean
MemoryPoolMBean proxy = JMX.newMBeanProxy( mbeanServer, objectName, MemoryPoolMBean.class); String name = proxy.getName(); MemoryUsage usage = proxy.getUsage(); long used = usage.getUsed();
MXBean
MemoryPoolMXBean proxy = JMX.newMXBeanProxy( mbeanServer, objectName, MemoryPoolMXBean.class); String name = proxy.getName(); MemoryUsage usage = proxy.getUsage(); long used = usage.getUsed();
Implementing the MemoryPool object works similarly for both Standard MBeans and MXBeans.
Standard MBean
public class MemoryPool implements MemoryPoolMBean { public String getName() {...} public MemoryUsage getUsage() {...} // ... }
MXBean
public class MemoryPool implements MemoryPoolMXBean { public String getName() {...} public MemoryUsage getUsage() {...} // ... }
Registering the MBean in the MBean Server works in the same way in both cases:
Standard MBean
{ MemoryPoolMBean pool = new MemoryPool(); mbeanServer.registerMBean(pool, objectName); }
MXBean
{ MemoryPoolMXBean pool = new MemoryPool(); mbeanServer.registerMBean(pool, objectName); }
Definition of an MXBean
An MXBean is a kind of MBean. An MXBean object can be registered directly in the MBean Server, or it can be used as an argument to StandardMBean
and the resultant MBean registered in the MBean Server.
When an object is registered in the MBean Server using the registerMBean
or createMBean
methods of the MBeanServer
interface, the object's class is examined to determine what type of MBean it is:
- If the class implements the interface
DynamicMBean
then the MBean is a Dynamic MBean. Note that the classStandardMBean
implements this interface, so this case applies to a Standard MBean or MXBean created using the classStandardMBean
. - Otherwise, if the class matches the Standard MBean naming conventions, then the MBean is a Standard MBean.
- Otherwise, it may be an MXBean. The set of interfaces implemented by the object is examined for interfaces that:
- have a class name
SMXBean
whereS
is any non-empty string, and do not have an annotation@MXBean(false)
; and/or - have an annotation
@MXBean(true)
or just@MXBean
.
MemoryPoolMXBean
. - have a class name
- If none of these conditions is met, the MBean is invalid and the attempt to register it will generate
NotCompliantMBeanException
.
Every Java type that appears as the parameter or return type of a method in an MXBean interface must be convertible using the rules below. Additionally, parameters must be reconstructible as defined below.
An attempt to construct an MXBean that does not conform to the above rules will produce an exception.
Naming conventions
The same naming conventions are applied to the methods in an MXBean as in a Standard MBean:
- A method
T getN()
, whereT
is a Java type (notvoid
) andN
is a non-empty string, specifies that there is a readable attribute calledN
. The Java type and Open type of the attribute are determined by the mapping rules below. The methodfinal Class getClass()
inherited fromObject
is ignored when looking for getters. - A method
boolean isN()
specifies that there is a readable attribute calledN
with Java typeboolean
and Open typeSimpleType.Boolean
. - A method
void setN(T x)
specifies that there is a writeable attribute calledN
. The Java type and Open type of the attribute are determined by the mapping rules below. (Of course, the namex
of the parameter is irrelevant.) - Every other method specifies that there is an operation with the same name as the method. The Java type and Open type of the return value and of each parameter are determined by the mapping rules below.
The rules for getN
and isN
collectively define the notion of a getter. The rule for setN
defines the notion of a setter.
It is an error for there to be two getters with the same name, or two setters with the same name. If there is a getter and a setter for the same name, then the type T
in both must be the same. In this case the attribute is read/write. If there is only a getter or only a setter, the attribute is read-only or write-only respectively.
Type mapping rules
An MXBean is a kind of Open MBean, as defined by the javax.management.openmbean
package. This means that the types of attributes, operation parameters, and operation return values must all be describable using Open Types, that is the four standard subclasses of OpenType
. MXBeans achieve this by mapping Java types into Open Types.
For every Java type J, the MXBean mapping is described by the following information:
- The corresponding Open Type, opentype(J). This is an instance of a subclass of
OpenType
. - The mapped Java type, opendata(J), which is always the same for any given opentype(J). This is a Java class.
- How a value is converted from type J to type opendata(J).
- How a value is converted from type opendata(J) to type J, if it can be.
For example, for the Java type List<String>
:
- The Open Type, opentype(
List<String>
), isArrayType
(1,
SimpleType.STRING
)
, representing a 1-dimensional array ofString
s. - The mapped Java type, opendata(
List<String>
), isString[]
. - A
List<String>
can be converted to aString[]
usingList.toArray(new String[0])
. - A
String[]
can be converted to aList<String>
usingArrays.asList
.
If no mapping rules exist to derive opentype(J) from J, then J cannot be the type of a method parameter or return value in an MXBean interface.
If there is a way to convert opendata(J) back to J then we say that J is reconstructible. All method parameters in an MXBean interface must be reconstructible, because when the MXBean framework is invoking a method it will need to convert those parameters from opendata(J) to J. In a proxy generated by JMX.newMXBeanProxy
, it is the return values of the methods in the MXBean interface that must be reconstructible.
Null values are allowed for all Java types and Open Types, except primitive Java types where they are not possible. When converting from type J to type opendata(J) or from type opendata(J) to type J, a null value is mapped to a null value.
The following table summarizes the type mapping rules.
Java type J | opentype(J) | opendata(J) |
---|---|---|
int , boolean , etc(the 8 primitive Java types) |
SimpleType.INTEGER ,SimpleType.BOOLEAN , etc |
Integer , Boolean , etc(the corresponding boxed types) |
Integer , ObjectName , etc(the types covered by SimpleType ) | the corresponding SimpleType
| J, the same type |
int[] etc(a one-dimensional array with primitive element type) |
ArrayType.getPrimitiveArrayType(int[].class) etc | J, the same type |
E[] (an array with non-primitive element type E; this includes int[][] , where E is int[] ) |
ArrayType.getArrayType( opentype(E))
|
opendata(E)[]
|
List< E> Set< E> SortedSet< E> (see below) | same as for E[]
| same as for E[]
|
An enumeration E (declared in Java as enum E {...} ) | SimpleType.STRING | String |
Map< K,V> SortedMap< K,V>
|
TabularType (see below) |
TabularData (see below) |
An MXBean interface |
SimpleType.OBJECTNAME (see below) |
ObjectName (see below) |
Any other type |
CompositeType , if possible(see below) | CompositeData |
The following sections give further details of these rules.
Mappings for primitive types
The 8 primitive Java types (boolean
, byte
, short
, int
,
long
, float
, double
, char
) are mapped to the corresponding boxed types from java.lang
, namely
Boolean
, Byte
, etc. The Open Type is the corresponding SimpleType
. Thus, opentype(
long
) is SimpleType.LONG
, and opendata(long
) is
java.lang.Long
.
An array of primitive type such as long[]
can be represented directly as an Open Type. Thus, openType(
long[]
) is
ArrayType.getPrimitiveArrayType(long[].class)
, and opendata(long[]
) is
long[]
.
In practice, the difference between a plain int
and
Integer
, etc, does not show up because operations in the JMX API are always on Java objects, not primitives. However, the difference does show up with arrays.
Mappings for collections (List<
E>
etc)
A List<
E>
or
Set<
E>
, such as List<String>
or
Set<ObjectName>
, is mapped in the same way as an array of the same element type, such as String[]
or
ObjectName[]
.
A SortedSet<
E>
is also mapped in the same way as an E[]
, but it is only convertible if E is a class or interface that implements Comparable
. Thus, a SortedSet<String>
or SortedSet<Integer>
is convertible, but a
SortedSet<int[]>
or SortedSet<List<String>>
is not. The conversion of a SortedSet
instance will fail with an IllegalArgumentException
if it has a non-null comparator()
.
A List<
E>
is reconstructed as a java.util.ArrayList<
E>
; a Set<
E>
as a java.util.HashSet<
E>
; a SortedSet<
E>
as a java.util.TreeSet<
E>
.
Mappings for maps (Map<
K,V>
etc)
A Map<
K,V>
or
SortedMap<
K,V>
, for example
Map<String,ObjectName>
, has Open Type TabularType
and is mapped to a TabularData
. The TabularType
has two items called key
and value
. The Open Type of key
is opentype(K), and the Open Type of value
is opentype(V). The index of the TabularType
is the single item key
.
For example, the TabularType
for a
Map<String,ObjectName>
might be constructed with code like this:
String typeName = "java.util.Map<java.lang.String, javax.management.ObjectName>"; String[] keyValue = new String[] {"key", "value"}; OpenType[] openTypes = new OpenType[] {SimpleType.STRING, SimpleType.OBJECTNAME}; CompositeType rowType = new CompositeType(typeName, typeName, keyValue, keyValue, openTypes); TabularType tabularType = new TabularType(typeName, typeName, rowType, new String[] {"key"});
The typeName
here is determined by the type name rules detailed below.
A SortedMap<
K,V>
is mapped in the same way, but it is only convertible if K is a class or interface that implements Comparable
. Thus, a SortedMap<String,int[]>
is convertible, but a SortedMap<int[],String>
is not. The conversion of a SortedMap
instance will fail with an
IllegalArgumentException
if it has a non-null comparator()
.
A Map<
K,V>
is reconstructed as a java.util.HashMap<
K,V>
; a SortedMap<
K,V>
as a java.util.TreeMap<
K,V>
.
TabularData
is an interface. The concrete class that is used to represent a Map<
K,V>
as Open Data is TabularDataSupport
, or another class implementing
TabularData
that serializes as TabularDataSupport
.
Mappings for MXBean interfaces
An MXBean interface, or a type referenced within an MXBean interface, can reference another MXBean interface, J. Then opentype(J) is SimpleType.OBJECTNAME
and opendata(J) is ObjectName
.
For example, suppose you have two MXBean interfaces like this:
public interface ProductMXBean { public ModuleMXBean[] getModules(); } public interface ModuleMXBean { public ProductMXBean getProduct(); }
The object implementing the ModuleMXBean
interface returns from its getProduct
method an object implementing the ProductMXBean
interface. The ModuleMXBean
object and the returned
ProductMXBean
objects must both be registered as MXBeans in the same MBean Server.
The method ModuleMXBean.getProduct()
defines an attribute called Product
. The Open Type for this attribute is SimpleType.OBJECTNAME
, and the corresponding ObjectName
value will be the name under which the referenced ProductMXBean
is registered in the MBean Server.
If you make an MXBean proxy for a ModuleMXBean
and call its getProduct()
method, the proxy will map the ObjectName
back into a ProductMXBean
by making another MXBean proxy. More formally, when a proxy made with JMX.newMXBeanProxy(mbeanServerConnection, objectNameX,
interfaceX)
needs to map objectNameY
back into
interfaceY
, another MXBean interface, it does so with
JMX.newMXBeanProxy(mbeanServerConnection, objectNameY,
interfaceY)
. The implementation may return a proxy that was previously created by a call to JMX.newMXBeanProxy
with the same parameters, or it may create a new proxy.
The reverse mapping is illustrated by the following change to the ModuleMXBean
interface:
public interface ModuleMXBean { public ProductMXBean getProduct(); public void setProduct(ProductMXBean c); }
The presence of the setProduct
method now means that the Product
attribute is read/write. As before, the value of this attribute is an ObjectName
. When the attribute is set, the ObjectName
must be converted into the ProductMXBean
object that the setProduct
method expects. This object will be an MXBean proxy for the given ObjectName
in the same MBean Server.
If you make an MXBean proxy for a ModuleMXBean
and call its setProduct
method, the proxy will map its ProductMXBean
argument back into an ObjectName
. This will only work if the argument is in fact another proxy, for a ProductMXBean
in the same
MBeanServerConnection
. The proxy can have been returned from another proxy (like ModuleMXBean.getProduct()
which returns a proxy for a ProductMXBean
); or it can have been created by JMX.newMXBeanProxy
; or it can have been created using Proxy
with an invocation handler that is MBeanServerInvocationHandler
or a subclass.
If the same MXBean were registered under two different ObjectName
s, a reference to that MXBean from another MXBean would be ambiguous. Therefore, if an MXBean object is already registered in an MBean Server and an attempt is made to register it in the same MBean Server under another name, the result is an InstanceAlreadyExistsException
. Registering the same MBean object under more than one name is discouraged in general, notably because it does not work well for MBeans that are NotificationBroadcaster
s.
Mappings for other types
Given a Java class or interface J that does not match the other rules in the table above, the MXBean framework will attempt to map it to a CompositeType
as follows. The type name of this CompositeType
is determined by the type name rules below.
The class is examined for getters using the conventions above. (Getters must be public instance methods.) If there are no getters, or if any getter has a type that is not convertible, then J is not convertible.
If there is at least one getter and every getter has a convertible type, then opentype(J) is a
CompositeType
with one item for every getter. If the getter is
T getName()then the item in the
CompositeType
is called name
and has type opentype(T). For example, if the item is String getOwner()then the item is called
owner
and has Open Type
SimpleType.STRING
. If the getter is boolean isName()then the item in the
CompositeType
is called name
and has type SimpleType.BOOLEAN
. Notice that the first character (or code point) is converted to lower case. This follows the Java Beans convention, which for historical reasons is different from the Standard MBean convention. In a Standard MBean or MXBean interface, a method getOwner
defines an attribute called Owner
, while in a Java Bean or mapped CompositeType
, a method
getOwner
defines a property or item called owner
.
If two methods produce the same item name (for example,
getOwner
and isOwner
, or getOwner
and
getowner
) then the type is not convertible.
When the Open Type is CompositeType
, the corresponding mapped Java type (opendata(J)) is CompositeData
. The mapping from an instance of J to a CompositeData
corresponding to the CompositeType
just described is done as follows. First, if J implements the interface CompositeDataView
, then that interface's toCompositeData
method is called to do the conversion. Otherwise, the CompositeData
is constructed by calling the getter for each item and converting it to the corresponding Open Data type. Thus, a getter such as
List<String> getNames()
will have been mapped to an item with name "names
" and Open Type ArrayType(1, SimpleType.STRING)
. The conversion to CompositeData
will call getNames()
and convert the resultant List<String>
into a String[]
for the item "names
".
CompositeData
is an interface. The concrete class that is used to represent a type as Open Data is CompositeDataSupport
, or another class implementing
CompositeData
that serializes as
CompositeDataSupport
.
Reconstructing an instance of Java type J from a CompositeData
If opendata(J) is CompositeData
for a Java type J, then either an instance of J can be reconstructed from a CompositeData
, or J is not reconstructible. If any item in the CompositeData
is not reconstructible, then J is not reconstructible either.
For any given J, the following rules are consulted to determine how to reconstruct instances of J from CompositeData
. The first applicable rule in the list is the one that will be used.
If J has a method
public static
Jfrom(CompositeData cd)
then that method is called to reconstruct an instance of J.-
Otherwise, if J has at least one public constructor with either
@javax.management.ConstructorParameters
or@java.beans.ConstructoProperties
annotation, then one of those constructors (not necessarily always the same one) will be called to reconstruct an instance of J. If a constructor is annotated with both@javax.management.ConstructorParameters
and@java.beans.ConstructorProperties
,@javax.management.ConstructorParameters
will be used and@java.beans.ConstructorProperties
will be ignored. Every such annotation must list as many strings as the constructor has parameters; each string must name a property corresponding to a getter of J; and the type of this getter must be the same as the corresponding constructor parameter. It is not an error for there to be getters that are not mentioned in the@ConstructorParameters
or@ConstructorProperties
annotations (these may correspond to information that is not needed to reconstruct the object).An instance of J is reconstructed by calling a constructor with the appropriate reconstructed items from the
CompositeData
. The constructor to be called will be determined at runtime based on the items actually present in theCompositeData
, given that thisCompositeData
might come from an earlier version of J where not all the items were present. A constructor is applicable if all the properties named in its@ConstructorParameters
or@ConstructorProperties
annotation are present as items in theCompositeData
. If no constructor is applicable, then the attempt to reconstruct J fails.For any possible combination of properties, it must be the case that either (a) there are no applicable constructors, or (b) there is exactly one applicable constructor, or (c) one of the applicable constructors names a proper superset of the properties named by each other applicable constructor. (In other words, there should never be ambiguity over which constructor to choose.) If this condition is not true, then J is not reconstructible.
-
Otherwise, if J has a public no-arg constructor, and for every getter in J with type T and name N there is a corresponding setter with the same name and type, then an instance of J is constructed with the no-arg constructor and the setters are called with the reconstructed items from the
CompositeData
to restore the values. For example, if there is a method
public List<String> getNames()
then there must also be a method
public void setNames(List<String> names)
for this rule to apply.If the
CompositeData
came from an earlier version of J, some items might not be present. In this case, the corresponding setters will not be called. Otherwise, if J is an interface that has no methods other than getters, an instance of J is constructed using a
Proxy
with aCompositeDataInvocationHandler
backed by theCompositeData
being converted.Otherwise, J is not reconstructible.
Rule 2 is not applicable when java.beans.ConstructorProperties
is not visible (e.g. when the java.desktop module is not readable or when the runtime image does not contain the java.desktop module). When targeting a runtime that does not include the java.beans
package, and where there is a mismatch between the compile-time and runtime environment whereby J is compiled with a public constructor and the ConstructorProperties
annotation, then J is not reconstructible unless another rule applies.
Here are examples showing different ways to code a type
NamedNumber
that consists of an int
and a
String
. In each case, the CompositeType
looks like this:
CompositeType( "NamedNumber", // typeName "NamedNumber", // description new String[] {"number", "name"}, // itemNames new String[] {"number", "name"}, // itemDescriptions new OpenType[] {SimpleType.INTEGER, SimpleType.STRING} // itemTypes );
- Static
from
method:public class NamedNumber { public int getNumber() {return number;} public String getName() {return name;} private NamedNumber(int number, String name) { this.number = number; this.name = name; } public static NamedNumber from(CompositeData cd) { return new NamedNumber((Integer) cd.get("number"), (String) cd.get("name")); } private final int number; private final String name; }
- Public constructor with
@ConstructorParameters
annotation:public class NamedNumber { public int getNumber() {return number;} public String getName() {return name;} @ConstructorParameters({"number", "name"}) public NamedNumber(int number, String name) { this.number = number; this.name = name; } private final int number; private final String name; }
- Setter for every getter:
public class NamedNumber { public int getNumber() {return number;} public void setNumber(int number) {this.number = number;} public String getName() {return name;} public void setName(String name) {this.name = name;} public NamedNumber() {} private int number; private String name; }
- Interface with only getters:
public interface NamedNumber { public int getNumber(); public String getName(); }
It is usually better for classes that simply represent a collection of data to be immutable. An instance of an immutable class cannot be changed after it has been constructed. Notice that CompositeData
itself is immutable. Immutability has many advantages, notably with regard to thread-safety and security. So the approach using setters should generally be avoided if possible.
Recursive types
Recursive (self-referential) types cannot be used in MXBean interfaces. This is a consequence of the immutability of CompositeType
. For example, the following type could not be the type of an attribute, because it refers to itself:
public interface Node { public String getName(); public int getPriority(); public Node getNext(); }
It is always possible to rewrite recursive types like this so they are no longer recursive. Doing so may require introducing new types. For example:
public interface NodeList { public List<Node> getNodes(); } public interface Node { public String getName(); public int getPriority(); }
MBeanInfo contents for an MXBean
An MXBean is a type of Open MBean. However, for compatibility reasons, its MBeanInfo
is not an OpenMBeanInfo
. In particular, when the type of an attribute, parameter, or operation return value is a primitive type such as int
, or is void
(for a return type), then the attribute, parameter, or operation will be represented respectively by an MBeanAttributeInfo
, MBeanParameterInfo
, or MBeanOperationInfo
whose getType()
or
getReturnType()
returns the primitive name ("int
" etc). This is so even though the mapping rules above specify that the opendata mapping is the wrapped type (Integer
etc).
The array of public constructors returned by MBeanInfo.getConstructors()
for an MXBean that is directly registered in the MBean Server will contain all of the public constructors of that MXBean. If the class of the MXBean is not public then its constructors are not considered public either. The list returned for an MXBean that is constructed using the StandardMBean
class is derived in the same way as for Standard MBeans. Regardless of how the MXBean was constructed, its constructor parameters are not subject to MXBean mapping rules and do not have a corresponding OpenType
.
The array of notification types returned by MBeanInfo.getNotifications()
for an MXBean that is directly registered in the MBean Server will be empty if the MXBean does not implement the NotificationBroadcaster
interface. Otherwise, it will be the result of calling NotificationBroadcaster.getNotificationInfo()
at the time the MXBean was registered. Even if the result of this method changes subsequently, the result of MBeanInfo.getNotifications()
will not. The list returned for an MXBean that is constructed using the StandardMBean
or StandardEmitterMBean
class is derived in the same way as for Standard MBeans.
The Descriptor
for all of the MBeanAttributeInfo
, MBeanParameterInfo
, and MBeanOperationInfo
objects contained in the MBeanInfo
will have a field openType
whose value is the OpenType
specified by the mapping rules above. So even when getType()
is "int
", getDescriptor().getField("openType")
will be SimpleType.INTEGER
.
The Descriptor
for each of these objects will also have a field originalType
that is a string representing the Java type that appeared in the MXBean interface. The format of this string is described in the section Type Names below.
The Descriptor
for the MBeanInfo
will have a field mxbean
whose value is the string "true
".
Type Names
Sometimes the unmapped type T of a method parameter or return value in an MXBean must be represented as a string. If T is a non-generic type, this string is the value returned by Class.getName()
. Otherwise it is the value of genericstring(T), defined as follows:
- If T is a non-generic non-array type, genericstring(T) is the value returned by
Class.getName()
, for example"int"
or"java.lang.String"
. - If T is an array E[], genericstring(T) is genericstring(E) followed by
"[]"
. For example, genericstring(int[]
) is"int[]"
, and genericstring(List<String>[][]
) is"java.util.List<java.lang.String>[][]"
. - Otherwise, T is a parameterized type such as
List<String>
and genericstring(T) consists of the following: the fully-qualified name of the parameterized type as returned byClass.getName()
; a left angle bracket ("<"
); genericstring(A) where A is the first type parameter; if there is a second type parameter B then", "
(a comma and a single space) followed by genericstring(B); a right angle bracket (">"
).
Note that if a method returns int[]
, this will be represented by the string "[I"
returned by
Class.getName()
, but if a method returns List<int[]>
, this will be represented by the string
"java.util.List<int[]>"
.
Exceptions
A problem with mapping from Java types to Open types is signaled with an OpenDataException
. This can happen when an MXBean interface is being analyzed, for example if it references a type like java.util.Random
that has no getters. Or it can happen when an instance is being converted (a return value from a method in an MXBean or a parameter to a method in an MXBean proxy), for example when converting from SortedSet<String>
to
String[]
if the SortedSet
has a non-null
Comparator
.
A problem with mapping to Java types from Open types is signaled with an InvalidObjectException
. This can happen when an MXBean interface is being analyzed, for example if it references a type that is not reconstructible according to the rules above, in a context where a reconstructible type is required. Or it can happen when an instance is being converted (a parameter to a method in an MXBean or a return value from a method in an MXBean proxy), for example from a String to an Enum if there is no Enum constant with that name.
Depending on the context, the OpenDataException
or InvalidObjectException
may be wrapped in another exception such as RuntimeMBeanException
or UndeclaredThrowableException
. For every thrown exception, the condition C will be true: "e is
OpenDataException
or InvalidObjectException
(as appropriate), or C is true of e.getCause()
".
- Since:
- 1.6
Optional Element Summary
Modifier and Type | Optional Element | Description |
---|---|---|
boolean | value | True if the annotated interface is an MXBean interface. |
Element Detail
value
boolean value
True if the annotated interface is an MXBean interface.
- Returns:
- true if the annotated interface is an MXBean interface.
- Default:
- true