EPICS exampleJava

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Overview

This project provides a set of examples of client and server code for pvAccess. Each example can be built separately by building in the example subdirectory. The complete set of examples can also be built by building in exampleJava itself.

Each Example is a template

Each example can be used as a template for building other applications:

• Choose an example that is similar to the desired application.
• Copy the complete example to where the desired application should reside.
• Edit the pom.xml file.
• Edit the new application

Building via exampleJava

Just type:

mvn package

Building An Individual Example

Just type:

mvn package

Brief summary of examples

database

Provides a server that has a database of V4 PVRecords.

exampleClient

Provides a set of examples that use pvaClientJava.

In order to run the examples, database must also be built and then started as follows:

mrk> pwd
/home/epicsv4/master/exampleJava/database/shell
mrk> ./exampleDatabase

helloPutGet

Implements a PVRecord that is an example of a PVRecord intended to be accessed via channelPutGet. It is a simple HelloWorld example.

helloRPC

A very simple example of an EPICS V4 RPC service: This implements a "Hello World" example of a service that is accessed via Channel RPC.

This is a starting point for writing an RPC service without using pvDatabaseJava.

But note that example database has a similar example implemented via pvDatabaseJava, which allows clients to monitor the result of each request.

exampleLink

This implements a V3 IOC that has a PVRecord doubleArray and a PVRecord exampleLink that monitors changes to doubleArray. PVRecord exampleLink uses pvAccess client code to monitor for changes in doubleArray. It can use either provider local, pva, or ca to connect to doubleArray.

powerSupply

This is an example of creating a PVRecord that uses a somewhat complicated top level PVStructure. It simulates a power supply.

The example also has an example pvaClient for accessing the PVRecord.

pvDatabaseRPC

An example of a pvDatabase PVRecord which also supports RPC services.

The record represents a 2-D position, but also provides an RPC service which moves the position through a sequence of points before returning. A channel to the record supports the usual operations (such as get, put and monitor) but also supports Channel RPC, i.e. the RPC service has the same channel name as the position PV.

A client ("move") for calling the service is supplied.

arrayPerformance

This is an example that shows performance for an array of longs.

arrayPerformanceMain implement a PVRecord that is a long array. It has a process method with code that causes the array to be updated at selectable rates and sizes.!

It also has pvaClient examples that can get, put, and monitor the long array record.

serviceAPI

Start with its RDBSERVICE_README.txt.

The rdbService example is a complete functional server for accessing SQL databases such Oracle via an EPICS V4 server, and returning the resulting table ResultSet data back to an EPICS V4 client. rdbService illustrates a number of facets of EPICS V4's, use for writing high performance synchronous servers, plus some other stuff:

1. channelRPC functionality of EPICSV4
2. use of JDBC for accessing Oracle to execute a SQL query within a pattern that retries the query and can rebuild the connection if any query fails - for high reliability and to make sure if the database back end ever cycles, the EPICS v4 server need not be restarted.
3. Passing string messages back to the client asynchronously - while the server is still processing the query - in the event of the server detecting an error or other detecting some other diagnostic.
4. Putting complex data into an EPICS V4 pvStructure (the basic complex data object of pvData), ready for returning results back to the EPICS V4 client. PvStructures are the basic mechanism for returning "structured" data between EPICS V4 clients and servers.
5. Client side calling the server, and getting the results.
6. Unpacking complex data out of a pvStructure
7. Illustration of the idea of using the NTTable EPICS V4 "normative type" (though the definition of an NTTable is likely to change soon)
8. Helpers for transformation of array pvData to Java Vectors
9. Formatting pvStructure encoded data for printing.
10. Use of the NTURI normative type, the EPICS V4 standard for passing requests for data and arguments.

The "serviceapi" package in src/org/epics/serviceAPI is composed of a single class server and a single class client, and is intended to illustrate the principles of RPC comms in EPICS V4. It shows how one defines and populates the pvStructure conforming to the NTURI Normative Type, for making an RPC query to a pvAccess server, and it shows how the server defines and populates a table of data conforming to the NTTable Normative Type for encoding the reply.

rdbService

Start with its RDBSERVICE_README.txt

rdbService is the classic hello world idea, implemented as a server and a client. The client sends an argument "your name" to the server, which replies just saying "hello that name". The server is built on top of the RPCSever framework in pvAccessJava.