[[Detyped_management_and_the_jboss-dmr_library]]
= Detyped management and the jboss-dmr library

ifdef::env-github[]
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:note-caption: :information_source:
:important-caption: :heavy_exclamation_mark:
:caution-caption: :fire:
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endif::[]

The management model exposed by WildFly is very large and complex. There
are dozens, probably hundreds of logical concepts involved – hosts,
server groups, servers, subsystems, datasources, web connectors, and on
and on – each of which in a classic objected oriented API design could
be represented by a Java _type_ (i.e. a Java class or interface.)
However, a primary goal in the development of WildFly's native
management API was to ensure that clients built to use the API had as
few compile-time and run-time dependencies on JBoss-provided classes as
possible, and that the API exposed by those libraries be powerful but
also simple and stable. A management client running with the management
libraries created for an earlier version of WildFly should still work if
used to manage a later version domain. The management client libraries
needed to be _forward compatible_.

It is highly unlikely that an API that consists of hundreds of Java
types could be kept forward compatible. Instead, the WildFly management
API is a _detyped_ API. A detyped API is like decaffeinated coffee – it
still has a little bit of caffeine, but not enough to keep you awake at
night. WildFly's management API still has a few Java types in it (it's
impossible for a Java library to have no types!) but not enough to keep
you (or us) up at night worrying that your management clients won't be
forward compatible.

A detyped API works by making it possible to build up arbitrarily
complex data structures using a small number of Java types. All of the
parameter values and return values in the API are expressed using those
few types. Ideally, most of the types are basic JDK types, like
`java.lang.String`, `java.lang.Integer`, etc. In addition to the basic
JDK types, WildFly's detyped management API uses a small library called
*jboss-dmr*. The purpose of this section is to provide a basic overview
of the jboss-dmr library.

Even if you don't use jboss-dmr directly (probably the case for all but
a few users), some of the information in this section may be useful.
When you invoke operations using the application server's Command Line
Interface, the return values are just the text representation of of a
jboss-dmr `ModelNode`. If your CLI commands require complex parameter
values, you may yourself end up writing the text representation of a
`ModelNode`. And if you use the HTTP management API, all response bodies
as well as the request body for any POST will be a JSON representation
of a `ModelNode`.

The source code for jboss-dmr is available on
https://github.com/jbossas/jboss-dmr[Github]. The maven coordinates for
a jboss-dmr release are `org.jboss.jboss-dmr:jboss-dmr`.

[[modelnode-and-modeltype]]
== ModelNode and ModelType

The public API exposed by jboss-dmr is very simple: just three classes,
one of which is an enum!

The primary class is `org.jboss.dmr.ModelNode`. A `ModelNode` is
essentially just a wrapper around some _value_; the value is typically
some basic JDK type. A `ModelNode` exposes a `getType()` method. This
method returns a value of type `org.jboss.dmr.ModelType`, which is an
enum of all the valid types of values. And that's 95% of the public API;
a class and an enum. (We'll get to the third class, `Property`, below.)

[[basic-modelnode-manipulation]]
=== Basic ModelNode manipulation

To illustrate how to work with `ModelNode` s, we'll use the
http://www.beanshell.org[Beanshell] scripting library. We won't get into
many details of beanshell here; it's a simple and intuitive tool and
hopefully the following examples are as well.

We'll start by launching a beanshell interpreter, with the jboss-dmr
library available on the classpath. Then we'll tell beanshell to import
all the jboss-dmr classes so they are available for use:

[source,options="nowrap"]
----
$ java -cp bsh-2.0b4.jar:jboss-dmr-1.0.0.Final.jar bsh.Interpreter
BeanShell 2.0b4 - by Pat Niemeyer (pat@pat.net)
bsh % import org.jboss.dmr.*;
bsh %
----

Next, create a `ModelNode` and use the beanshell `print` function to
output what type it is:

[source,options="nowrap"]
----
bsh % ModelNode node = new ModelNode();
bsh % print(node.getType());
UNDEFINED
----

A new `ModelNode` has no value stored, so its type is
`ModelType.UNDEFINED`.

Use one of the overloaded `set` method variants to assign a node's
value:

[source,options="nowrap"]
----
bsh % node.set(1);
bsh % print(node.getType());
INT
bsh % node.set(true);
bsh % print(node.getType());
BOOLEAN
bsh % node.set("Hello, world");
bsh % print(node.getType());
STRING
----

Use one of the `asXXX()` methods to retrieve the value:

[source,options="nowrap"]
----
bsh % node.set(2);
bsh % print(node.asInt());
2
bsh % node.set("A string");
bsh % print(node.asString());
A string
----

`ModelNode` will attempt to perform type conversions when you invoke the
`asXXX` methods:

[source,options="nowrap"]
----
bsh % node.set(1);
bsh % print(node.asString());
1
bsh % print(node.asBoolean());
true
bsh % node.set(0);
bsh % print(node.asBoolean());
false
bsh % node.set("true");
bsh % print(node.asBoolean());
true
----

Not all type conversions are possible:

[source,options="nowrap"]
----
bsh % node.set("A string");
bsh % print(node.asInt());
// Error: // Uncaught Exception: Method Invocation node.asInt : at Line: 20 : in file: <unknown file> : node .asInt ( )

Target exception: java.lang.NumberFormatException: For input string: "A string"

java.lang.NumberFormatException: For input string: "A string"
 at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
 at java.lang.Integer.parseInt(Integer.java:449)
 at java.lang.Integer.parseInt(Integer.java:499)
 at org.jboss.dmr.StringModelValue.asInt(StringModelValue.java:61)
 at org.jboss.dmr.ModelNode.asInt(ModelNode.java:117)
        ....
----

The `ModelNode.getType()` method can be used to ensure a node has an
expected value type before attempting a type conversion.

One `set` variant takes another `ModelNode` as its argument. The value
of the passed in node is copied, so there is no shared state between the
two model nodes:

[source,options="nowrap"]
----
bsh % node.set("A string");
bsh % ModelNode another = new ModelNode();
bsh % another.set(node);
bsh % print(another.asString());
A string
bsh % node.set("changed");
bsh % print(node.asString());
changed
bsh % print(another.asString());
A string
----

A `ModelNode` can be cloned. Again, there is no shared state between the
original node and its clone:

[source,options="nowrap"]
----
bsh % ModelNode clone = another.clone();
bsh % print(clone.asString());
A string
bsh % another.set(42);
bsh % print(another.asString());
42
bsh % print(clone.asString());
A string
----

Use the `protect()` method to make a `ModelNode` immutable:

[source,options="nowrap"]
----
bsh % clone.protect();
bsh % clone.set("A different string");
// Error: // Uncaught Exception: Method Invocation clone.set : at Line: 15 : in file: <unknown file> : clone .set ( "A different string" )

Target exception: java.lang.UnsupportedOperationException

java.lang.UnsupportedOperationException
 at org.jboss.dmr.ModelNode.checkProtect(ModelNode.java:1441)
 at org.jboss.dmr.ModelNode.set(ModelNode.java:351)
        ....
----

[[lists]]
=== Lists

The above examples aren't particularly interesting; if all we can do
with a `ModelNode` is wrap a simple Java primitive, what use is that?
However, a `ModelNode`'s value can be more complex than a simple
primitive, and using these more complex types we can build complex data
structures. The first more complex type is `ModelType.LIST`.

Use the `add` methods to initialize a node's value as a list and add to
the list:

[source,options="nowrap"]
----
bsh % ModelNode list = new ModelNode();
bsh % list.add(5);
bsh % list.add(10);
bsh % print(list.getType());
LIST
----

Use `asInt()` to find the size of the list:

[source,options="nowrap"]
----
bsh % print(list.asInt());
2
----

Use the overloaded `get` method variant that takes an int param to
retrieve an item. The item is returned as a `ModelNode`:

[source,options="nowrap"]
----
bsh % ModelNode child = list.get(1);
bsh % print(child.asInt());
10
----

Elements in a list need not all be of the same type:

[source,options="nowrap"]
----
bsh % list.add("A string");
bsh % print(list.get(1).getType());
INT
bsh % print(list.get(2).getType());
STRING
----

*Here's one of the trickiest things about jboss-dmr:* _The_ `get`
_methods actually mutate state; they are not "read-only"_. For example,
calling `get` with an index that does not exist yet in the list will
actually create a child of type `ModelType.UNDEFINED` at that index (and
will create UNDEFINED children for any intervening indices.)

[source,options="nowrap"]
----
bsh % ModelNode four = list.get(4);
bsh % print(four.getType());
UNDEFINED
bsh % print(list.asInt());
6
----

Since the `get` call always returns a `ModelNode` and never `null` it is
safe to manipulate the return value:

[source,options="nowrap"]
----
bsh % list.get(5).set(30);
bsh % print(list.get(5).asInt());
30
----

That's not so interesting in the above example, but later on with node
of type `ModelType.OBJECT` we'll see how that kind of method chaining
can let you build up fairly complex data structures with a minimum of
code.

Use the `asList()` method to get a `List<ModelNode>` of the children:

[source,options="nowrap"]
----
bsh % for (ModelNode element : list.asList()) {
print(element.getType());
}
INT
INT
STRING
UNDEFINED
UNDEFINED
INT
----

The `asString()` and `toString()` methods provide slightly differently
formatted text representations of a `ModelType.LIST` node:

[source,options="nowrap"]
----
bsh % print(list.asString());
[5,10,"A string",undefined,undefined,30]
bsh % print(list.toString());
[
    5,
    10,
    "A string",
    undefined,
    undefined,
    30
]
----

Finally, if you've previously used `set` to assign a node's value to
some non-list type, you cannot use the `add` method:

[source,options="nowrap"]
----
bsh % node.add(5);
// Error: // Uncaught Exception: Method Invocation node.add : at Line: 18 : in file: <unknown file> : node .add ( 5 )

Target exception: java.lang.IllegalArgumentException

java.lang.IllegalArgumentException
 at org.jboss.dmr.ModelValue.addChild(ModelValue.java:120)
 at org.jboss.dmr.ModelNode.add(ModelNode.java:1007)
 at org.jboss.dmr.ModelNode.add(ModelNode.java:761)
        ...
----

You can, however, use the `setEmptyList()` method to change the node's
type, and then use `add`:

[source,options="nowrap"]
----
bsh % node.setEmptyList();
bsh % node.add(5);
bsh % print(node.toString());
[5]
----

[[dmr-properties]]
=== Properties

The third public class in the jboss-dmr library is
`org.jboss.dmr.Property`. A `Property` is a `String => ModelNode` tuple.

[source,options="nowrap"]
----
bsh % Property prop = new Property("stuff", list);
bsh % print(prop.toString());
org.jboss.dmr.Property@79a5f739
bsh % print(prop.getName());
stuff
bsh % print(prop.getValue());
[
    5,
    10,
    "A string",
    undefined,
    undefined,
    30
]
----

The property can be passed to `ModelNode.set`:

[source,options="nowrap"]
----
bsh % node.set(prop);
bsh % print(node.getType());
PROPERTY
----

The text format for a node of `ModelType.PROPERTY` is:

[source,options="nowrap"]
----
bsh % print(node.toString());
("stuff" => [
    5,
    10,
    "A string",
    undefined,
    undefined,
    30
])
----

Directly instantiating a `Property` via its constructor is not common.
More typically one of the two argument `ModelNode.add` or
`ModelNode.set` variants is used. The first argument is the property
name:

[source,options="nowrap"]
----
bsh % ModelNode simpleProp = new ModelNode();
bsh % simpleProp.set("enabled", true);
bsh % print(simpleProp.toString());
("enabled" => true)
bsh % print(simpleProp.getType());
PROPERTY
bsh % ModelNode propList = new ModelNode();
bsh % propList.add("min", 1);
bsh % propList.add("max", 10);
bsh % print(propList.toString());
[
    ("min" => 1),
    ("max" => 10)
]
bsh % print(propList.getType());
LIST
bsh % print(propList.get(0).getType());
PROPERTY
----

The `asPropertyList()` method provides easy access to a
`List<Property>`:

[source,options="nowrap"]
----
bsh % for (Property prop : propList.asPropertyList()) {
print(prop.getName() + " = " + prop.getValue());
}
min = 1
max = 10
----

[[modeltype.object]]
=== ModelType.OBJECT

The most powerful and most commonly used complex value type in jboss-dmr
is `ModelType.OBJECT`. A `ModelNode` whose value is `ModelType.OBJECT`
internally maintains a `Map<String, ModelNode`.

Use the `get` method variant that takes a string argument to add an
entry to the map. If no entry exists under the given name, a new entry
is added with a the value being a `ModelType.UNDEFINED` node. The node
is returned:

[source,options="nowrap"]
----
bsh % ModelNode range = new ModelNode();
bsh % ModelNode min = range.get("min");
bsh % print(range.toString());
{"min" => undefined}
bsh % min.set(2);
bsh % print(range.toString());
{"min" => 2}
----

Again *it is important to remember that the* `get` *operation may mutate
the state of a model node by adding a new entry.* _It is not a read-only
operation._

Since `get` will never return `null`, a common pattern is to use method
chaining to create the key/value pair:

[source,options="nowrap"]
----
bsh % range.get("max").set(10);
bsh % print(range.toString());
{
    "min" => 2,
    "max" => 10
}
----

A call to `get` passing an already existing key will of course return
the same model node as was returned the first time `get` was called with
that key:

[source,options="nowrap"]
----
bsh % print(min == range.get("min"));
true
----

Multiple parameters can be passed to `get`. This is a simple way to
traverse a tree made up of `ModelType.OBJECT` nodes. Again, `get` may
mutate the node on which it is invoked; e.g. it will actually create the
tree if nodes do not exist. This next example uses a workaround to get
beanshell to handle the overloaded `get` method that takes a variable
number of arguments:

[source,options="nowrap"]
----
bsh % String[] varargs = { "US", "Missouri", "St. Louis" };
bsh % salesTerritories.get(varargs).set("Brian");
bsh % print(salesTerritories.toString());
{"US" => {"Missouri" => {"St. Louis" => "Brian"}}}
----

The normal syntax would be:

....
salesTerritories.get("US", "Missouri", "St. Louis").set("Brian");
....

The key/value pairs in the map can be accessed as a `List<Property`:

[source,options="nowrap"]
----
bsh % for (Property prop : range.asPropertyList()) {
print(prop.getName() + " = " + prop.getValue());
}
min = 2
----

The semantics of the backing map in a node of `ModelType.OBJECT` are
those of a `LinkedHashMap`. The map remembers the order in which
key/value pairs are added. This is relevant when iterating over the
pairs after calling `asPropertyList()` and for controlling the order in
which key/value pairs appear in the output from `toString()`.

Since the `get` method will actually mutate the state of a node if the
given key does not exist, `ModelNode` provides a couple methods to let
you check whether the entry is there. The `has` method simply does that:

[source,options="nowrap"]
----
bsh % print(range.has("unit"));
false
bsh % print(range.has("min"));
true
----

Very often, the need is to not only know whether the key/value pair
exists, but whether the value is defined (i.e. not
`ModelType.UNDEFINED`. This kind of check is analogous to checking
whether a field in a Java class has a null value. The `hasDefined` lets
you do this:

[source,options="nowrap"]
----
bsh % print(range.hasDefined("unit"));
false
bsh % // Establish an undefined child 'unit';
bsh % range.get("unit");
bsh % print(range.toString());
{
    "min" => 2,
    "max" => 10,
    "unit" => undefined
}
bsh % print(range.hasDefined("unit"));
false
bsh % range.get("unit").set("meters");
bsh % print(range.hasDefined("unit"));
true
----

[[modeltype.expression]]
=== ModelType.EXPRESSION

A value of type `ModelType.EXPRESSION` is stored as a string, but can
later be _resolved_ to different value. The string has a special syntax
that should be familiar to those who have used the system property
substitution feature in previous JBoss AS releases.

[source,options="nowrap"]
----
[<prefix>][${<system-property-name>[:<default-value>]}][<suffix>]*
----

For example:

....
${queue.length}
http://${host}
http://${host:localhost}:${port:8080}/index.html
....

Use the `setExpression` method to set a node's value to type expression:

[source,options="nowrap"]
----
bsh % ModelNode expression = new ModelNode();
bsh % expression.setExpression("${queue.length}");
bsh % print(expression.getType());
EXPRESSION
----

Calling `asString()` returns the same string that was input:

[source,options="nowrap"]
----
bsh % print(expression.asString());
${queue.length}
----

However, calling `toString()` tells you that this node's value is not of
`ModelType.STRING`:

[source,options="nowrap"]
----
bsh % print(expression.toString());
expression "${queue.length}"
----

When the `resolve` operation is called, the string is parsed and any
embedded system properties are resolved against the JVM's current system
property values. A new `ModelNode` is returned whose value is the
resolved string:

[source,options="nowrap"]
----
bsh % System.setProperty("queue.length", "10");
bsh % ModelNode resolved = expression.resolve();
bsh % print(resolved.asInt());
10
----

Note that the type of the `ModelNode` returned by `resolve()` is
`ModelType.STRING`:

[source,options="nowrap"]
----
bsh % print(resolved.getType());
STRING
----

The `resolved.asInt()` call in the previous example only worked because
the string "10" happens to be convertible into the int 10.

Calling `resolve()` has no effect on the value of the node on which the
method is invoked:

[source,options="nowrap"]
----
bsh % resolved = expression.resolve();
bsh % print(resolved.toString());
"10"
bsh % print(expression.toString());
expression "${queue.length}"
----

If an expression cannot be resolved, `resolve` just uses the original
string. The string can include more than one system property
substitution:

[source,options="nowrap"]
----
bsh % expression.setExpression("http://${host}:${port}/index.html");
bsh % resolved = expression.resolve();
bsh % print(resolved.asString());
http://${host}:${port}/index.html
----

The expression can optionally include a default value, separated from
the name of the system property by a colon:

[source,options="nowrap"]
----
bsh % expression.setExpression("http://${host:localhost}:${port:8080}/index.html");
bsh % resolved = expression.resolve();
bsh % print(resolved.asString());
http://localhost:8080/index.html
----

Actually including a system property substitution in the expression is
not required:

[source,options="nowrap"]
----
bsh % expression.setExpression("no system property");
bsh % resolved = expression.resolve();
bsh % print(resolved.asString());
no system property
bsh % print(expression.toString());
expression "no system property"
----

The `resolve` method works on nodes of other types as well; it returns a
copy without attempting any real resolution:

[source,options="nowrap"]
----
bsh % ModelNode basic = new ModelNode();
bsh % basic.set(10);
bsh % resolved = basic.resolve();
bsh % print(resolved.getType());
INT
bsh % resolved.set(5);
bsh % print(resolved.asInt());
5
bsh % print(basic.asInt());
10
----

In addition to system properties, in the above examples, we also support substituting
from environment variables. See the <<Expression_Resolution, Expression Resolution>>
subsection for a more thorough description of how this works in practice.

[[modeltype.type]]
=== ModelType.TYPE

You can also pass one of the values of the `ModelType` enum to `set`:

[source,options="nowrap"]
----
bsh % ModelNode type = new ModelNode();
bsh % type.set(ModelType.LIST);
bsh % print(type.getType());
TYPE
bsh % print(type.toString());
LIST
----

This is useful when using a `ModelNode` data structure to describe
another `ModelNode` data structure.

[[full-list-of-modelnode-types]]
=== Full list of ModelNode types

BIG_DECIMAL +
BIG_INTEGER +
BOOLEAN +
BYTES +
DOUBLE +
EXPRESSION +
INT +
LIST +
LONG +
OBJECT +
PROPERTY +
STRING +
TYPE +
UNDEFINED

[[text-representation-of-a-modelnode]]
=== Text representation of a ModelNode

TODO – document the grammar

[[json-representation-of-a-modelnode]]
=== JSON representation of a ModelNode

TODO – document the grammar
