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Date: Fri, 22 Jan 2016 18:30:55 +0530
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 <CABAipVancCr2Ac58kaHxp+bhz1MjMJsqNKgxcDxMnM49-1w3Jg@mail.gmail.com>
Subject: Re: Ability to generate POJO class on the fly
From: Chinmay Kolhatkar <chinmay@datatorrent.com>
To: dev@apex.incubator.apache.org
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Hi Priyanka,

Can you give an example?

Thanks,
Chinmay.

~ Chinmay
On 22 Jan 2016 18:14, "Priyanka Gugale" <priyanka@datatorrent.com> wrote:

> We do need configuration in some form like json, but I was thinking we can
> have default wherever possible. This is an option and not replacement to
> json config.
>
> -Priyanka
>
> On Fri, Jan 22, 2016 at 4:34 PM, Chinmay Kolhatkar <
> chinmay@datatorrent.com>
> wrote:
>
> > @priyanka
> >
> > Advantage with JSON schema is that one can represent nested POJO
> definition
> > in that. If you're referring to FieldInfo, I'm not sure if that is
> possible
> > there.
> >
> > Even if we chose not to have nested POJO now, I think JSON schema input
> to
> > this utility gives more chance to expand easily later.
> >
> >
> >
> > On Fri, Jan 22, 2016 at 3:30 PM, Chinmay Kolhatkar <
> > chinmay@datatorrent.com>
> > wrote:
> >
> > > Sure. We can make this utility to provide byte[] for compiled class.
> > > Though the utility will give a OutputStream object.. One can get byte[]
> > > out of that.
> > >
> > > On Fri, Jan 22, 2016 at 2:56 PM, Timothy Farkas <tim@datatorrent.com>
> > > wrote:
> > >
> > >> Suggestion: +1 for automatic generation of schema. The user should be
> > able
> > >> to override the a manually specified schema though.
> > >>
> > >> Question: If the mechanism used to generate the class can produce a
> > byte[]
> > >> array, then you can send the byte[] array for the class to downstream
> > >> operators and load the class from the byte[] array in each operator.
> An
> > >> example of how to do this is here:
> > >>
> > >>
> > >>
> >
> http://stackoverflow.com/questions/1781091/java-how-to-load-class-stored-as-byte-into-the-jvm
> > >>
> > >> Thanks,
> > >> Tim
> > >>
> > >> On Fri, Jan 22, 2016 at 12:59 AM, Priyanka Gugale <
> > >> priyanka@datatorrent.com>
> > >> wrote:
> > >>
> > >> > Hi,
> > >> >
> > >> > Suggestion:
> > >> > This came up with one of the discussion with Pramod, will it be a
> good
> > >> > idea, for database input operators to generate pojo based on the
> > >> selected
> > >> > column field names and types? No need to accept json input from
> user.
> > >> >
> > >> > Question:
> > >> > How can we share this POJO among multiple operators when application
> > is
> > >> > already launched and class is generated on the fly?
> > >> >
> > >> > -Priyanka
> > >> >
> > >> > On Thu, Jan 21, 2016 at 11:16 PM, Chinmay Kolhatkar <
> > >> > chinmay@datatorrent.com
> > >> > > wrote:
> > >> >
> > >> > > Hi All,
> > >> > >
> > >> > > We're planning to add a utility in malhar-library for generating a
> > >> POJO
> > >> > > class on the fly from given JSON schema.
> > >> > >
> > >> > > Use case is where the application is provided with schema and that
> > >> needs
> > >> > to
> > >> > > be used in one or more operators either as a tuple over the stream
> > OR
> > >> for
> > >> > > processing.
> > >> > >
> > >> > > General Design:
> > >> > > 1. Utility will be provided with fqcn of the class and schema
> > >> definition
> > >> > > provided as json.
> > >> > > 2. The schema definition will look like following:
> > >> > >     {
> > >> > >        "fqcn":"<qualified class name>",
> > >> > >        "fields": [
> > >> > >          {
> > >> > >            "name":"field1",
> > >> > >            "type":"long"
> > >> > >          },
> > >> > >          {
> > >> > >            "name":"field2",
> > >> > >            "type": "string"
> > >> > >          }
> > >> > >        ]
> > >> > >     }
> > >> > > 3. Supported types identified in "type" JSON field are:
> > >> > >       boolean, char, byte, short, int, float, long, double
> > >> > > 4. The output of this utility will be a generated .class file in
> the
> > >> form
> > >> > > of FSDataOutputStream.
> > >> > > 5. Xbean asm5 library will be used for this.
> > >> > > 6. Following methods will be added to the generated class:
> > >> > >     a. Getter/Setter methods for given fields.
> > >> > >     b. simple toString - Generate string equivalent for all the
> > fields
> > >> > >     c. hashCode method - calculate the overall hashCode using
> > >> individual
> > >> > > field hashcodes, similar to how String.hashCode generates hashCode
> > of
> > >> > > string using chars in it.
> > >> > >     d. equals method - Similar to how String.equals method has
> done
> > it
> > >> > > using individual char.
> > >> > >
> > >> > >
> > >> > > Questions I have about the functionality:
> > >> > > 1. Should the utility also support nested pojo definition via
> schema
> > >> > json?
> > >> > >     In such case the field definition can look like following:
> > >> > >     { "name":"nestedField", "type":"<fqcn of nested class>",
> > >> > > "fields":[....] }
> > >> > >     The nested class will be provided
> > >> > >
> > >> > > 2. Should the utility also support giving out the JarOutputStream
> > >> which
> > >> > > will have a generated jar?
> > >> > >
> > >> > > Please let me know your thoughts.
> > >> > >
> > >> > > Thanks,
> > >> > > Chinmay.
> > >> > >
> > >> >
> > >>
> > >
> > >
> >
>

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