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README.md

Zserio Java Quick Start Tutorial

This Quick Start tutorial features code generation in Java. Go to the Zserio C++ tutorial or Zserio Python tutorial if you are interested in hands-on C++ or Python with zserio.

You find the complete tutorial in this example. To follow along the description just clone this repo and check the sources. For convenience and compatibility reasons, we have included the zserio.jar compiler and the corresponded runtime in this repository. The zserio compiler is located in the project's root folder and the runtime library is in subfolder 3rdparty.

The latest build of the zserio compiler and runtime library can be get from Zserio Releases.

If you want to build from source, please follow the Zserio Compiler Build Instructions.

Installation & Prerequisites

Before we start, make sure you have the following components installed:

  • Java JDK

Set up dev environment

Everything has been already set up for you in this repository. If you are very impatient, just go to the project's root folder and have a quick look to the schema tutorial.zs. Then, run the following commands:

mkdir build
javac -d build -cp 3rdparty/runtime/zserio_runtime.jar src/Main.java src/**/*.java

Now, start to play with tutorial executable using the command:

java -cp 3rdparty/runtime/zserio_runtime.jar:build Main

We start with a common layout of our project/repo where we put all the source files into a src folder and all 3rd party stuff into 3rdparty. For simplicity the zserio schema file stays in the project's root folder.

So our folder structure looks like this:

.
├───3rdparty
│   └───runtime
└───src

Now we only need to generate the code, populate the Main.java and we are done.

But before we can generate code, we need to write the schema definition of our data.

Writing a schema

Open up your favorite text editor and start writing your schema. We will use the example from the zserio repo plus some additional structures to showcase some of zserio's features.

package tutorial;

struct Employee
{
    uint8           age : age <= 65; // max age is 65
    string          name;
    uint16          salary;
    optional uint16 bonus;
    Role            role;

    // if employee is a developer, list programming skill
    Experience      skills[] if role == Role.DEVELOPER;
};

struct Experience
{
    bit:6       yearsOfExperience;
    Language    programmingLanguage;
};

enum bit:2 Language
{
    CPP     = 0,
    JAVA    = 1,
    PYTHON  = 2,
    JS      = 3
};

enum uint8 Role
{
    DEVELOPER = 0,
    TEAM_LEAD = 1,
    CTO       = 2
};

We have added some of zserio's features above. Let's quickly take a look:

  • Constraints

    Although the uint8 of field age would allow values up to 255, we limit the use already in the schema definition by using a constraint. If we try to write values larger than 65, the generated writers will throw an exception.

  • Optional fields

    The bonus field is prefixed with the keyword optional which will add a invisible 1-bit bool before that field which indicating whether the field exists. If it is not set then only one bit will be added to the bit stream. See Zserio Invisibles for more information.

  • Conditions

    We add programming skills only if the employee is developer.

  • Bit sized elements

    The struct Experience uses 1 byte in total. It uses 6 bit to store the years of programming experience and 2 bits for the enum Language.

For more details on the features of zserio head over to the Zserio Language Overview.

We now save the file to disk as tutorial.zs.

Please note that the filename has to be equivalent to the package name inside the zserio file. The zserio compiler accepts arbitrary file extensions (in this case *.zs). But make sure that all imported files also have the same file extension.

Compiling and generating code

Now we are ready to compile the schema with the zserio compiler. The zserio compiler checks the schema file and its imported files and reports errors and warnings. In addition, the zserio compiler generates code for the supported languages and may generate HTML documentation. For a complete overview of available options, please refer to the Zserio Compiler User Guide.

So let's generate some Java code:

java -jar zserio.jar -java src tutorial.zs

This command generates Java code and puts it into the src folder. It actually creates subfolders for each package in the schema.

So after generating the code our folder structure looks like this:

.
├───3rdparty
│   └───runtime
└───src
    └───tutorial

Let's take a quick look what has been generated. In the src/tutorial folder you now find the following files:

Employee.java  Experience.java  Language.java  Role.java

There is one Java file for each struct or enum.

We now have everything ready to serialize and deserialize our data.

Serialize using the generated code

Note: The example code in this repository features the creation of two objects of class Employee: Joe and his boss. We will mostly cover the creation of Joe here.

Before we start programming, let's have compile our project:

mkdir build
javac -d build -cp 3rdparty/runtime/zserio_runtime.jar src/Main.java src/**/*.java

Then open up your favorite IDE and start using the zserio classes by importing the classes from the schema and zserio runtime that we want to use.

import zserio.runtime.ZserioError;
import zserio.runtime.array.ObjectArray;
import zserio.runtime.io.FileBitStreamReader;
import zserio.runtime.io.FileBitStreamWriter;

import tutorial.Employee;
import tutorial.Language;
import tutorial.Role;
import tutorial.Experience;

Let's declare an employee Joe and fill in some data:

/* declare an employee */
final Employee joe = new Employee();

/* fill some basic type fields */
joe.setAge((short) 32);
joe.setName("Joe Smith");
joe.setSalary(5000);

/* set an enum value, in this case the role */
joe.setRole(Role.DEVELOPER);

To be able to populate a list of skills, we need to declare a ArrayList object of type Experience:

final List<Experience> skills = new ArrayList<Experience>();

So now let's generate two entries for the skills list:

First we add C++ experience:

Experience skill1 = new Experience((byte) 8, Language.CPP);
skills.add(skill1);

and then also some Python experience:

Experience skill2 = new Experience((byte) 4, Language.PYTHON);
skills.add(skill2);

Don't forget to set Joe's skills:

joe.setSkills(new ObjectArray<Experience>(skills));

Class 'ObjectArray' is zserio object array from runtime library. You can find a full list of available zserio arrays in the Zserio Java API overview.

After we have set all the fields, we have to declare a FileBitStreamWriter and write the stream to the file:

final FileBitStreamWriter writer = new FileBitStreamWriter(employeeFile);

/* serialize the object joe by passing the BitStreamWriter to its write() method */
joe.write(writer);
writer.close();

Voila! You have just serialized your first data with zserio.

Congratulations!

Deserialize using the generated code

We already pointed out that Joe has a boss in the code we checked in. In the deserialization code we need to keep an eye on all possible serializations we might have to deal with. So let's quickly look at the differences between Joe and his boss.

Joe's boss is a little older, has a higher salary, gets a bonus but has no programming skills, because our schema definition does not allow team leads to have programming skills. ;-)

/* set an enum value, in this case the role */
boss.setRole(Role.TEAM_LEAD);

/* no programming skills for the boss, but a bonus! */
boss.setBonus(10000);

The rest is pretty similar. Check the code to see the rest.

When deserializing the zserio bit stream, we start with reading the file using FileBitStreamReader declaration:

final FileBitStreamReader reader = new FileBitStreamReader(employeeFile);

We declare an object of class Employee and deserialize the buffer with the help of the FileBitStreamReader we just created. After this call all the fields within employee will be set.

final Employee employee = new Employee();
employee.read(reader);

We can now access the filled employee object via the respective getters. We still need to check for optionals and conditionals whether they have been set.

/* print out the contents of Employee */
System.out.println("Name: " + employee.getName());
System.out.println("Age: " + employee.getAge());
System.out.println("Salary: " + employee.getSalary());
System.out.println("Role: " + employee.getRole());

/* we have to check for optionals whether they are in the stream */
if (employee.hasBonus())
    System.out.println("Bonus: " + employee.getBonus());

For the rest of the processing please refer to the code. You should have gotten the main point by now.

Additions you will find in the code

There are some other features that we used in the code in this repo that we would like to point out briefly:

  • zserio runtime exception handling
  • some zserio API calls

Zserio runtime exceptions

The zserio runtime throws two exceptions. The zserio.runtime.ZserioError and the java.io.IOException.

It makes sense to try-catch all of your writes and reads as we do in our tutorial:

try
{
    // read or write
}
catch (ZserioError e)
{
    System.out.println("ZserioError caught: " + e.getMessage());
}
catch (IOException e)
{
    System.out.println("IOException caught: " + e.getMessage());
}

Examples for when an exception will be thrown:

  • Data type range exceptions

    Zserio types get mapped to Java native types of a bigger type sometimes (e.g. bit:2 to short). You may assign values that fit into the Java native type which will compile fine, but the zserio runtime will throw an exception if it does not fit into the zserio schema.

    Example: Try to give Joe a programming experience of 100 years.

  • Constraint exceptions

    If there is a constrain in the schema that requires a certain field to be set to specific value, the zserio runtime will throw an exception if you try to set the field without the constraint being met.

    Example: Try to make Joe 100 years old.

Zserio API calls

The example uses one smaller feature that we would like to explain.

The feature is that you can always retrieve the actual bit size of the structures in zserio by calling bitSizeOf().

In the tutorial we use it for plain informational purpose only.

System.out.println("Bit size of employee: " + employee.bitSizeOf());
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