1. Overview
In this article, we will discover how to develop cross-platform client-server applications with the help of RPC framework called Apache Thrift.
We will cover:
- Defining data types and service interfaces with IDL
- Installing the library and generating the sources for different languages
- Implementing the defined interfaces in particular language
- Implementing client/server software
If you want to go straight to examples, proceed straight to section 5.
2. Apache Thrift
Apache Thrift was originally developed by the Facebook development team and is currently maintained by Apache.
In comparison to Protocol Buffers, which manage cross-platform object serialization/deserialization processes, Thrift mainly focuses on the communication layer between components of your system.
Thrift uses a special Interface Description Language (IDL) to define data types and service interfaces which are stored as .thrift files and used later as input by the compiler for generating the source code of client and server software that communicate over different programming languages.
To use Apache Thrift in your project, add this Maven dependency:
<dependency>
<groupId>org.apache.thrift</groupId>
<artifactId>libthrift</artifactId>
<version>0.10.0</version>
</dependency>
You can find the latest version in the Maven repository.
3. Interface Description Language
As already described, IDL allows defining of communication interfaces in a neutral language. Below you will find the currently supported types.
3.1. Base Types
- bool – a boolean value (true or false)
- byte – an 8-bit signed integer
- i16 – a 16-bit signed integer
- i32 – a 32-bit signed integer
- i64 – a 64-bit signed integer
- double – a 64-bit floating point number
- string – a text string encoded using UTF-8 encoding
3.2. Special Types
- binary – a sequence of unencoded bytes
- optional – a Java 8’s Optional type
3.3. Structs
Thrift structs are the equivalent of classes in OOP languages but without inheritance. A struct has a set of strongly typed fields, each with a unique name as an identifier. Fields may have various annotations (numeric field IDs, optional default values, etc.).
3.4. Containers
Thrift containers are strongly typed containers:
- list – an ordered list of elements
- set – an unordered set of unique elements
- map<type1,type2> – a map of strictly unique keys to values
Container elements may be of any valid Thrift type.
3.5. Exceptions
Exceptions are functionally equivalent to structs, except that they inherit from the native exceptions.
3.6. Services
Services are actually communication interfaces defined using Thrift types. They consist of a set of named functions, each with a list of parameters and a return type.
4. Source Code Generation
4.1. Language Support
There’s a long list of currently supported languages:
- C++
- C#
- Go
- Haskell
- Java
- Javascript
- Node.js
- Perl
- PHP
- Python
- Ruby
You can check the full list here.
4.2. Using Library’s Executable File
Just download the latest version, build and install it if necessary, and use the following syntax:
cd path/to/thrift
thrift -r --gen [LANGUAGE] [FILENAME]
In the commands set above, [LANGUAGE] is one of the supported languages and [FILENAME] is a file with IDL definition.
Note the -r flag. It tells Thrift to generate code recursively once it notices includes in a given .thrift file.
4.3. Using Maven Plugin
Add the plugin in your pom.xml file:
<plugin>
<groupId>org.apache.thrift.tools</groupId>
<artifactId>maven-thrift-plugin</artifactId>
<version>0.1.11</version>
<configuration>
<thriftExecutable>path/to/thrift</thriftExecutable>
</configuration>
<executions>
<execution>
<id>thrift-sources</id>
<phase>generate-sources</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
</executions>
</plugin>
After that just execute the following command:
mvn clean install
Note that this plugin will not have any further maintenance anymore. Please visit this page for more information.
5. Example of a Client-Server Application
5.1. Defining Thrift File
Let’s write some simple service with exceptions and structures:
namespace cpp com.baeldung.thrift.impl
namespace java com.baeldung.thrift.impl
exception InvalidOperationException {
1: i32 code,
2: string description
}
struct CrossPlatformResource {
1: i32 id,
2: string name,
3: optional string salutation
}
service CrossPlatformService {
CrossPlatformResource get(1:i32 id) throws (1:InvalidOperationException e),
void save(1:CrossPlatformResource resource) throws (1:InvalidOperationException e),
list <CrossPlatformResource> getList() throws (1:InvalidOperationException e),
bool ping() throws (1:InvalidOperationException e)
}
As you can see, the syntax is pretty simple and self-explanatory. We define a set of namespaces (per implementation language), an exception type, a struct, and finally a service interface which will be shared across different components.
Then just store it as a service.thrift file.
5.2. Compiling and Generating a Code
Now it’s time to run a compiler which will generate the code for us:
thrift -r -out generated --gen java /path/to/service.thrift
As you might see, we added a special flag -out to specify the output directory for generated files. If you did not get any errors, the generated directory will contain 3 files:
- CrossPlatformResource.java
- CrossPlatformService.java
- InvalidOperationException.java
Let’s generate a C++ version of the service by running:
thrift -r -out generated --gen cpp /path/to/service.thrift
Now we get 2 different valid implementations (Java and C++) of the same service interface.
5.3. Adding a Service Implementation
Although Thrift has done most of the work for us, we still need to write our own implementations of the CrossPlatformService. In order to do that, we just need to implement a CrossPlatformService.Iface interface:
public class CrossPlatformServiceImpl implements CrossPlatformService.Iface {
@Override
public CrossPlatformResource get(int id)
throws InvalidOperationException, TException {
return new CrossPlatformResource();
}
@Override
public void save(CrossPlatformResource resource)
throws InvalidOperationException, TException {
saveResource();
}
@Override
public List<CrossPlatformResource> getList()
throws InvalidOperationException, TException {
return Collections.emptyList();
}
@Override
public boolean ping() throws InvalidOperationException, TException {
return true;
}
}
5.4. Writing a Server
As we said, we want to build a cross-platform client-server application, so we need a server for it. The great thing about Apache Thrift is that it has its own client-server communication framework which makes communication a piece of cake:
public class CrossPlatformServiceServer {
public void start() throws TTransportException {
TServerTransport serverTransport = new TServerSocket(9090);
server = new TSimpleServer(new TServer.Args(serverTransport)
.processor(new CrossPlatformService.Processor<>(new CrossPlatformServiceImpl())));
System.out.print("Starting the server... ");
server.serve();
System.out.println("done.");
}
public void stop() {
if (server != null && server.isServing()) {
System.out.print("Stopping the server... ");
server.stop();
System.out.println("done.");
}
}
}
First thing is to define a transport layer with the implementation of TServerTransport interface (or abstract class, to be more precise). Since we are talking about server, we need to provide a port to listen to. Then we need to define a TServer instance and choose one of the available implementations:
- TSimpleServer – for simple server
- TThreadPoolServer – for multi-threaded server
- TNonblockingServer – for non-blocking multi-threaded server
And finally, provide a processor implementation for chosen server which was already generated for us by Thrift, i.e. CrossPlatofformService.Processor class.
5.5. Writing a Client
And here is the client’s implementation:
TTransport transport = new TSocket("localhost", 9090);
transport.open();
TProtocol protocol = new TBinaryProtocol(transport);
CrossPlatformService.Client client = new CrossPlatformService.Client(protocol);
boolean result = client.ping();
transport.close();
From a client perspective, the actions are pretty similar.
First of all, define the transport and point it to our server instance, then choose the suitable protocol. The only difference is that here we initialize the client instance which was, once again, already generated by Thrift, i.e. CrossPlatformService.Client class.
Since it is based on .thrift file definitions we can directly call methods described there. In this particular example, client.ping() will make a remote call to the server which will respond with true.
6. Conclusion
In this article, we’ve shown you the basic concepts and steps in working with Apache Thrift, and we’ve shown how to create a working example which utilizes Thrift library.
As usually, all the examples can be always found over in the GitHub repository.
