MATLAB: When deploying a Web App, why does MATLAB code fail to instantiate an object

MATLAB Compiler

I have developed an app and deployed it onto a web app server. The MATLAB code fails at recognizing an object called "strat".

Then, I get the following warning message and an error afterwards:

Warning: Variable 'a' originally saved as a strat cannot be instantiated as an object
and will be read in as a uint32

Best Answer

When using classes in a deployed component, the class definition will also have to be complied into the deployed component. Usually the dependency analysis will do this, but it does not look at the dependency inside the MAT-files that the code is trying to load. Therefore, the issue you are facing is probably due to trying to load a saved object from a MAT-file.

To resolve this issue make sure the class definition is compiled into the deployed component. There are a few ways to do this:

1) Use the '%#function' pragma. Please follow the link below to view the documentation for more details:

https://www.mathworks.com/help/compiler_sdk/ml_code/function.html

2) By manually adding the class to the "files required by your application to run" in the compiler app.

3) Use the 'mcc' command to the input argument option set as '-a'. Please follow the link below to view the documentation for more details:

https://www.mathworks.com/help/compiler/mcc.html

Related Solutions

MATLAB: How to attach libraries when compiling code that uses “batch”

This workflow requires that you specify the additional libraries and files through both the "batch" function and "mcc". This way, the client will have the necessary files to send over with "batch".

For "batch", the "AttachedFiles" parameter can be used to specify the necessary files and folders to send to the worker:

j = batch('myScript','AttachedFiles',{'mscr1.m','mscr2.m'});

For "mcc", the "-a" option can be used to add additional files and folders to the compilation.

mcc -m hello.m -a ./testdir

MATLAB: Do I get java class IMPORT errors when compiling a deployed application using MATLAB Compiler 4.16 (R2012a)

This bug has been fixed in Release 2012b (R2012b). For previous product releases, read below for any possible workarounds:

This is a bug in MATLAB Compiler 4.16 (R2012a). Possible workarounds are:

1. Instead of using

import com.google.common.base.Stopwatch;

where the full class name is defined, use

import com.google.common.base.*;

2. It is also possible to encapsulate the IMPORT statements inside MATLAB Class objects, such as:

classdef someclass
    methods
        function helloworld(obj)
            import com.google.common.base.Stopwatch;
            disp('Hello, world!');
        end
    end
end

In this case, you still get the warning

 Error: File: T:\1-GOVY7I\repro_import_build_error\repro_import_build_error\standalone_hello.m Line: 2 Column: 8 
 Arguments to IMPORT must either end with ".*" 
  or else specify a fully qualified class name: "com.google.common.base.Stopwatch" fails this test.

but the compilation will continue and generate a working component.

3. Add the java class JAR file into MATLAB's static java class path (instead of using JAVAADDPATH, which adds to dynamic class path). To do this, you need to add the JAR file path into MATLAB's classpath.txt file located at

matlabroot\toolbox\local\classpath.txt

where matlabroot is MATLAB's installation directory. Editing the classpath.txt file should be avoided if possible, as any mistake can cause MATLAB to crash upon startup.

Best Answer

Related Solutions

MATLAB: How to attach libraries when compiling code that uses “batch”

MATLAB: Do I get java class IMPORT errors when compiling a deployed application using MATLAB Compiler 4.16 (R2012a)

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