Types

Topics covered in this chapter:

The jvmobject type

You can use the jvmobject type to hold a Java object reference within your Mosel model. A jvmobject initially contains a null reference but can be populated as the return value of jvmcallobj, e.g.:

declarations
  myobj: jvmobject
end-decarations
myobj := jvmcallobj("com.fico.examples.ConfigOperations.getConfigFile","config.dat")

Once the jvmobject is populated, you can check it's populated using getisnull and check if it's of the expected class using getclass, e.g.:

declarations
  myobj: jvmobject
end-decarations
myobj := jvmcallobj("com.fico.examples.ConfigOperations.getConfigFile","config.dat")
if myobj.isnull then
  writeln('ERROR: Expected configuration File object, found null')
elif myobj.class<>'java.io.File' then
  writeln('ERROR: Expected configuration File object, found '+myobj.class)
end-if

You can also turn it to a string or text (which uses the Java toString() method), or pass it to other public Java functions, e.g.:

declarations
  myobj: jvmobject
  configfiles: array(range) of text
end-decarations
myobj := jvmcallobj("com.fico.examples.ConfigOperations.getConfigFile","config.dat")
configfiles(configfiles.size+1) := text(myobj)
writeln('About to read configuration from file ',myobj)
jvmcallvoid("com.fico.examples.ConfigOperations.loadConfigFromFile",myobj);

If the jvmobject contains a java.lang.Number, a java.lang.String or a java.lang.Boolean, you can read the value into a Mosel variable, e.g.:

declarations
  myobj: jvmobject
  b: boolean
  i: integer
  r: real
  t: text
end-decarations
myobj := jvmcallobj("com.fico.examples.ConfigOperations.getConfigValue","value1")
if myobj.class='java.lang.Integer' then
  i := myobj.intvalue
elif myobj.class='java.lang.Boolean' then
  b := myobj.boolvalue
elif myobj.class='java.lang.Double' then
  r := myobj.realvalue
elif myobj.class='java.lang.String' then
  t := myobj.textvalue
end-if

You can construct a new Java object and store it in a jvmobject by using the jvmnewobj function, e.g.:

declarations
  myobj: jvmobject
end-decarations
myobj := jvmnewobj("java.io.File","C:/myfiles/mydatafile.csv")

Finally, you can also populate a jvmobject with any of these basic types (the Java object will be created automatically based on the type of the value you provide), e.g.:

declarations
  i,b,r,t: jvmobject
end-decarations
i.value := 1
b.value := true
r.value := 9.1
t.value := 'hello world'

Attributes

The jvmobject type supports attributes allowing different types of object reference to be read/written:

The jvmmethod type

The jvmmethod type holds a Java object reference to a java.lang.reflect.Method or java.land.reflect.Constructor object. Typically jvmmethod values are created by jvmfindmethod, jvmfindstaticmethod or jvmfindconstructor calls and then passed to jvmcall* functions such as jvmcallvoid or jvmnewobjinstead of a class/method name, for those cases where the developer wants to specify exactly which overload of a method name should be called. For example:

model myModel
  uses 'mosjvm'

  declarations
    mth: jvmmethod
  end-declarations

  ! Look up method myMethod on class MyClass which takes a java.lang.Number as a parameter
  mth := jvmfindmethod('com.fico.MyClass', 'myMethod', ['java.lang.Number'])

  ! Call it
  jvmcall(mth, 123)
end-model

jvmmethod values can be converted to/from jvmobject; for example if you want to use the standard Java reflection API to look up a method to call:

model myModel
  uses 'mosjvm'

  declarations
    stringClass: jvmobject
    lengthMethod: jvmobject
    myString: jvmmethod
  end-declarations

  ! Populate with dummy data
  myString.string := 'hello world'

  ! Look up length method in String class
  stringClass := jvmcallobj('java.lang.class.forName', 'java.lang.String')
  lengthMethod := jvmmethod(jvmcallobj(stringClass, 'getDeclaredMethod', 'length'))

  ! Call the method
  writeln('Length of Java string = ', jvmcallint(myString, lengthMethod))
end-model

A jvmmethod initially contains a null reference; you can check it's populated using the isnull attribute.