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Tars File Reference

Tars protocol is a protocol based on IDL. Similar to Protocol Buffer, it is language-independent and is a C ++-like identifier language which is used to generate specific service interface files. At the same time, as a binary protocol, compared with common text protocols such as JSON, it has higher encoding and decoding efficiency and smaller network packet space.

The Tars file uses .tars as the extension. For each service in the .tars file, a Java interface will be generated when generating the code. If the server interface code is generated, the Servant suffix will be added. If the code is generated for the client, the Prx suffix will be added. For the grammar rules of Tars language, please refer to Tars protocol.


Tars-maven-plugin needs to add related dependencies in the pom.xml file:

<!--tars2java plugin-->
			<!-- tars file location -->
			<!-- Source file encoding -->
			<!-- Generate server code -->
			<!-- Generated source code encoding -->
			<!-- Generated source code directory -->
			<!-- Generated source code package prefix -->

Some of the configurations are as follows:

Server Tars file

Take hello.tars on the server side in tars-quick-start as an example:

module TestApp
	interface Hello
	    string hello(int no, string name);

TestApp is the namespace, and all structs and interfaces must be in the namespace.

When generating the server code, you need to set the servant tag in the tars-maven-plugin dependency in the pom.xml file to true and then run the mvn tars: tars2java command in the root directory of the project to obtain the interface file with the suffix Servant,

public interface HelloServant {

	public String hello(int no, String name);

After that, the interface can be implemented according to the business logic.

Client Tars file

When making a service call on the client, you first need to obtain the tars file on the server side, and then you need to set the servant tag in the tars-maven-plugin dependency in the pom.xml file to false when generating the client code. Finally run the mvn tars: tars2java command in the root directory of the project to obtain the interface file with the suffix Prx,

public interface HelloPrx {

	 String hello(int no, String name);

	CompletableFuture<String>  promise_hello(int no, String name);

	 String hello(int no, String name, @TarsContext java.util.Map<String, String> ctx);

	 void async_hello(@TarsCallback HelloPrxCallback callback, int no, String name);

	 void async_hello(@TarsCallback HelloPrxCallback callback, int no, String name, @TarsContext java.util.Map<String, String> ctx);

The interface provides three calling modes:

Synchronous invoke

This is a blocking invoke method, the client will block until the server returns.

Asynchronous invoke

In addition, is also generated when the client code is generated, which is an abstract class for ordinary asynchronous callback processing:

public abstract class HelloPrxCallback extends TarsAbstractCallback {

	public abstract void callback_hello(String ret);


This class extends the abstract class TarsAbstractCallback:

@TarsCallback(comment = "Callback")
public abstract class TarsAbstractCallback implements<TarsServantResponse> {

    public final void onCompleted(TarsServantResponse response) {
        TarsServantRequest request = response.getRequest();
        try {
            Method callback = getCallbackMethod("callback_".concat(request.getFunctionName()));
            callback.invoke(this, ((TarsCodec) response.getSession().getProtocolFactory().getDecoder()).decodeCallbackArgs(response));
        } catch (Throwable ex) {
            throw new ClientException(ex);

    private Method getCallbackMethod(String methodName) throws NoSuchMethodException {
        Method[] methods = getClass().getDeclaredMethods();
        for (Method method : methods) {
            if (methodName.equals(method.getName())) {
                return method;
        throw new NoSuchMethodException("no such method " + methodName);

    public final void onException(Throwable ex) {

    public final void onExpired() {

    public abstract void callback_exception(Throwable ex);

    public abstract void callback_expired();

By implementing the callback_exception, callback_expired and callback_hello functions, the corresponding callback logic can be executed.

Promise invoke

The asynchronous promise call is a new feature of Tars v1.7.0. This method returns a CompletableFuture object. CompletableFuture is a newly added class in jdk1.8. It implements the Future <T> and CompletionStage <T> interfaces and provides very powerful asynchronous programming functions. Before jdk1.8, we mainly used Future or registered callback function to complete asynchronous programming. However, these two methods have certain defects. When Future invokes get() to get the result, if the operation is not completed, it will wait all the time, which may cause a waste of CPU time. Furthermore, Future cannot complete chained calls, and cannot perform further operations on the results obtained from the previous Future. For the callback method, with the continuous nesting of callback functions, it will cause the phenomenon of callback pyramid. Therefore, CompletableFuture was introduced in Tars v1.7.0, which can perform a series of subsequent operations in a callback manner by registering triggers.

The API of CompletabileFuture generally has two forms: the one with Async suffix and the one without Async suffix. The method without the Async suffix will be executed by the current calling thread, and the method with the Async suffix is divided into two cases. If Executor is passed in the parameter, a thread will be obtained from the Executor to execute the task. Otherwise, a thread obtained from the global ForkJoinPool.commonPool () will perform these tasks.