Table of Contents

Development of FEWS Adapter

...

1. The general adapter is that part of DELFT-FEWS which exports model input, imports model output data, and executes the pre-adapter, module and post-adapter.
2. Export and import of model data is done in datafiles following the Published Interface (PI) XML format.
3. The preAdapter, Module and postAdapter together form the model adapter. The model adapter is initiated from the general adapter.
4. The preAdapter is that part of the model adapter which converts input data in PI XML format to native model input data.
5. The postAdapter is that part of the model adapter which converts native model output data to PI XML format to be imported by FEWS.
6. The Module is that part of the model adapter which starts a model simulation.

...

External Modules and their adapters can be written in any programming language. However, in case Java is used, they have to implement the interface ModuleAdapterRunnable. Modules and module adapters can only communicate with the General Adapter via the Published Interface. The only 2 means to exchange information with the General Adapter are:

• A diagnostic file written in the Published Interface format. If such a diagnostic file is available the General Adapter will read it and write corresponding logs to the FEWS system.

• The return code indicating the result of an execution.

  return code	meaning
  non Zero	graceful failure - read message
  0	successful execution

  
  

Modules and their adapters cannot use exception or event handling as a means to communicate with the General Adapter.

...

Diagnostics file
The published interface documentation describes the (simple) xml file format. Per batch (pre processing - module run - post processing) one diagnostics file is always expected. Each line/message in this file contains the actual text and the warning level attached to this text. The warning levels in the diagnostics file will be interpreted by the general adapter. according to the following table:

All levels higher than 3 are regarded as non-essential (debug) information. The warnings are recorded in the system, but no actions will be taken.

In memory file transfer
The Java adapters should check if a file is transferred in memory to the adapter by FEWS.

public static BufferedInputStream newInputStream(File file) throws IOException {
    //noinspection UseOfPropertiesAsHashtable
    var stream = System.getProperties().get(file);
    if (stream instanceof BufferedInputStream) return (BufferedInputStream) stream;
    return new BufferedInputStream(new FileInputStream(file));
}

public static BufferedOutputStream newOutputStream(File file) throws IOException {
    //noinspection UseOfPropertiesAsHashtable
    var stream = System.getProperties().get(file);
    if (stream instanceof BufferedOutputStream) return (BufferedOutputStream) stream;
    return new BufferedOutputStream(new FileOutputStream(file));
}

Validating xml

When an adapter reads xml written by FEWS according to its own xsd there is no need for validation, it is an unnecessary step because in the creation process FEWS uses those xsd's and therefore the xml will be valid.

Since FEWS 2022.02 access to external xsd's from other xsd's is closed off for the Java xml package which is included in the jdk. This is done by setting the javax.xml.accessExternalSchema sytem property to an empty string for security reasons.

When existing adapters do use this and it is not an option to update the adapter, since FEWS stable2022.02 patch #118458 in clientConfig.xml the javax.xml.accessExternalSchema system property can be overruled via

<jvmOption>-Djavax.xml.accessExternalSchema=all</jvmOption>

Example model adapter (includes source code)

...

FEWS_Example_Model_Adapter.39413.zip