Serialization in Java is a mechanism that converts an objects state into a byte stream. The following demo shows how to use Hessian for serialization: Like Protobuf and Thrift, Hessian supports RPC communication across languages. The below described DeserializeDemo program deserializes the above Employee object created in the Serialize Demo program. Therefore, if serialization time consumption is a key metric, choose Kryo or FST. Now well call serialization method by passing the file name and path as the first parameter file.txt and dataObject as the second parameter. The following figure shows the serialization and deserialization time consumption. The following table lists the data types and syntax supported by serialization frameworks. Byte Stream It is a low level I/O operation and does not have any encoding scheme. The Input and Output encapsulate almost all stream operations. Thrift supports the following Java data types: Thrift does not support defining Java methods. Serialization in Java Example 1 : SerializationDemo.java. Communication: If two machines that are running the same code need to communicate, the easy way out is that one machine should build an object containing information that it would transmit and then serialize that object before sending it to the other machine. public static void main(String args[]) { The corresponding time consumption is listed below: The time consumption of Thrift is very close to Protobuf in serialization and deserialization.
In addition, no cross-language practices of Kryo are found on the Internet. In order to get our output we will print toString() method of data value object class. Avro is a data serialization framework. io. public String toString() { The Java program should have a buffered approach for I/O operations to process Byte Stream. Direct serialization will result in the following exception: Runnable Lambda does not implement the interfaces of JDK Serializable. Set a default value for all fields. The above method can be used to serialize an Object. Users can use the serialization mechanism of Java by implementing java.io.Serializable or java.io.Externalizable. Avro supports the basic Java data types (null, Boolean, int, long, float, double, bytes, and string) and complex Java data types (Record, Enum, Array, Map, Union, and Fixed.). Serializable in java is a marker interface. }. Protobuf uses interface definition language (IDL) to define the schema description file. The following demo shows how to use FST for serialization. return client; Deserialization is its reverse process. The exception above occurs because serialVersionUID is not defined but generated automatically by JDK Serializable through the hash algorithm. Therefore, the results of serialization and deserialization are inconsistent. Next, use TSerializer and TDeserializer to serialize and deserialize objects. A stream is simply a sequence of data elements. The field name cannot be modified, but an alias can be added. return store; public void setPasswordKeys(String passwordKeys) { Java methods cannot be defined in serialized classes. In this article you learned about how to serialize and deserialize an object. Although JDK Serializable is exclusive for Java, its performance is not so good. Although some articles have mentioned that the cross-language use of Kryo is very complicated, no related implementation in other languages is found. The latest FST version is 2.56. dataObject.setId(hhhhh); Such a mechanism persists the object. All fields of the class must be serializable. Serialization in Java Example 2 : SerializationImplDemo.java. We create an Employee class to study some features, and the code for the same is provided below. Modify the code below to serialize Lambda expressions: Fast-serialization (FST) is a Java serialization framework that is fully compatible with the JDK serialization protocol. This article compares open-source serialization frameworks in the industry by the universality, usability, scalability, performance, and supports for Java data types and syntax. Data Stream Data Stream allows to read-write primitive data types and used to perform binary I/O operations on primitive data types. public void close() throws IOException {}. Protobuf does not support defining Java methods because it uses IDL to define schemas. Therefore, cross-language serialization and deserialization are not supported. It is a sub-project of Apache Hadoop and a data serialization framework developed by Doug Cutting while he was in charge of Hadoop. which well be covering in our next article. Perform the same serialization operation on the test sample using Protobuf. Java Data types supported by the serialization frameworks: Note: The collection class tests cover most corresponding implementation classes.
It only needs to implement the Serializable interface for serialized data. Both the classes ObjectInputStream and ObjectOutputStream are high-level streams and extend java.io.InputStream and java.io.OutputStream. Hessian is often used as a serialization framework because it supports cross-language and efficient binary serialization protocol. store : Programming Concepts In ObjectInputStream class we call the readObject() method which will carry out the actual deserialization. public String getPasswordKeys() { It shows how Protobuf is the best because it supports multiple programming languages. JDK Serializable is a serialization framework of Java. If a class object is to be serialized, then one needs to implement the java.io.Serializable interface. Serialization in Java is implemented by the two classesObjectInputStreamandObjectOutputStream. The deserialization method retrieves the object from a stream and deserializes the same. However, there are different serialization methods to serialize an object such as Serialization with Inheritance, Serialization with Aggregation, Serialization with static data number, Serialization with array or collection etc. JDK Serializable uses serialVersionUID to control the version of a serialized class. Kryo provides rich and flexible configurations, such as serializer customization and default serializer setting, but they are difficult to use. You may also look at the following article to learn more , Java Training (40 Courses, 29 Projects, 4 Quizzes). In terms of usability, FST is much better than JDK Serializable. Kryo is a fast and effective Java binary serialization framework. Once the object is serialized into written into a file, it can be read from the file and deserialized which means that the type of information and bytes that represent the object can be utilized to create object in the memory. The following demo shows encoding and decoding using JDK Serializable: JDK Serializable is a built-in serialization framework of Java. As Hessian uses Java self-description to serialize classes, the native data types, collection classes, custom classes, and enumeration types of Java are mostly supported (SynchronousQueue is not supported.) } Thrift is similar to Protobuf in terms of usability. Protobuf consumes less time in serialization than Thrift, while Thrift is better in deserialization. During deSerialize method we open the file in read mode using FileInputStream class and pass the object to BufferedInputStream class constructor. By doing so, JDK Serializable can support field extension. One FSTConfiguration can be called by multiple threads. This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy. Later, Facebook made Thrift open-source to Apache.
What type of CPU was used for executing the benchmarks? dataObject.setStore(Programming store); By signing up, you agree to our Terms of Use and Privacy Policy. The implementation of serialization interfaces means only the class can be serialized or deserialized. Deep Copy: If an exactreplica of an Object needs to be created and writing a specialized clone class is too much hard work, then only serializing the object and then de-serializing it to another object will achieve the goal. passwordKeys : null. (2) Use the compiler of Thrift to generate Java code: (3) Use TSerializer and TDeserializer for encoding and decoding: Similar to Protobuf, Thrift also uses IDL to define the description file. Lets understand the need for serialization in our concluding remarks. The class must implement a serializable interface. The encoding and decoding demo above is not user-friendly.
The byte size after serialization is 120 because the identity of the serialized class is a number instead of the class name. The class ObjectOutputStream, a serialization class mentioned in the above section, contains several writing methods for writing various data types, but one method is the most popular. The following table compares the universality of different serialization frameworks. This article compares open-source serialization frameworks in the industry by the universality, usability, scalability, performance, and supports for Java data types and syntax. The try/catch block above tries to catch a ClassNotFoundException. The following table lists the time consumption: Avro needs to use supported data types to write schema information. The following test sample will also be used for all other frameworks. A low-code development platform to make work easier, Help enterprises build high-quality, stable mobile apps. When this program is done with executing, a file named employee.ser would be created. Add fields: To add fields, make sure that the new fields have corresponding default values to interact with the old code. To make an object serializable we use java.io.Serializable interface.
Because of the same, the deserialized Employee SSN field object is 0. The object is then passed to the constructor class ObjectInputStream while instantiating. 3. transient private String id; So, if the byte size after serialization is restricted, choose Kryo or Avro. public final Object readObject() throws IOException, ClassNotFoundException{}. } Therefore, to use Protobuf, users simply need to prepare the description file.
All Java classes generated from Slice definitions implement the java.io.Serializable interface. this.passwordKeys = passwordKeys; The following table shows the time consumption of serialization and deserialization. @Override FST has supported Android since version 2.17. The scalability of Protobuf is the most convenient and natural. Use FST to serialize the test sample using JDK Serializable. Java Serialization API contains methods for serialization and deserialization. What is the difference between Augmented reality (AR) and Virtual Reality (VR) ? Protobuf has made a lot of efforts in scalability so it can support protocol extensions. Therefore, these functions cannot be tested. Above, we introduced serialization concepts and provided examples. It uses HTTP protocol to transmit data and supports binary serialization. Lets understand streams in computer systems before proceeding further. The following table displays the supports of Protobuf for data types: Note: List, Set, and Queue collection classes are defined and tested through the "repeated" modifier in Protobuf. Protocol Buffer (Protobuf) is a language-neutral, platform-independent, and scalable serialization framework. I/O operations can be performed for byte, char, boolean, short, int, long, float, double and strings efficiently and conveniently. However, for static languages, such as Java, avro-tools.jar is still necessary to compile and generate Java code. It relies on the underlying ASM library to generate bytecode, so it runs quickly. }, Serialization in Java Example 3 : DataObject.java, public class DataObject implements Serializable{. However, the current variety of serialization frameworks confuses people about the selection of serialization frameworks in different scenarios. Use Avro to serialize objects in the following three steps: (2) Use avro-tools.jar or Maven to compile and generate Java code: (3) Use BinaryEncoder and BinaryDecoder for encoding and decoding: Avro defines the data structure through schemas. This number will be compared to the other serialization frameworks. Calling serialization and deserialization methods. On the official website, Kryo is described as a Java binary serialization framework. The time consumed for serialization in FST is the shortest, while the time consumed for serialization and deserialization in Kryo are almost the same. Thank you for this excellent article, this is very informative. When deserialized the value of these transient fields will have the default value. The process of serialization is instance independent which means an object can be serialized on one platform and deserialized on an entirely different platform. The popular method to read an object in ObjectInputStream is: This method reads the stream of bytes and converts it back to an object which is called deserialization. Different data streams in the computer systems are: 1. Of course, your client and server code must have an implementation of JavaClass that derives from java.io.Serializable: You can implement this class in any way you see fit the Ice run time does not place any other requirements on the implementation. If a field is deleted after being added, the compatibility will be affected. Hessian 2.0 optimizes the serialization process, and its performance is significantly improved compared with Hessian 1.0. The default Kryo serializer FiledSerializer does not support field extension. Note: The corresponding Input.readxxx function must be used when using the Output.writeXxx function. This will read an object from the input stream. DataObject dataObject = new DataObject(); Apache Flink Community China - September 16, 2020. A class is made serializable by this process which looks like an Opt-In process. Thrift does not include short and char types, which are replaced with double and String types.
To perform serialization using Thrift, create the Thrift IDL file first and then compile the file to generate Java code. Although Hessian needs to implement the Serializable interface to serialize classes, it is not affected by serialVersionUID and supports field extension easily. The return value is again an object, so all that is needed is to cast it to a relevant data type. It is more complicated to write a Schema in Avro than in Thrift and Protobuf. Scalability is also one of the goals of Protobuf design. public void setStore(String store) { Persistence: If the state of operation is to be stored in a database, it is first serialized to a byte array and then stored in the database for retrieval at a later point in time. If the Serializer is implemented, users need to control the Version. Kryo aims to provide a serialization framework with fast serialization speed, small result size, and simple APIs. We protect those fields from getting saved during the process of serialization. In Java UNICODE system is followed to store characters as character stream. Avro does not need to generate code for dynamic languages. When we run our Serialization in Java program we can now observe the following output: client : Yolanda 2022 - EDUCBA. Using the keyword transient before any field of an object wont get serialized since transient objects are not eligible for serialization. } This will flush the current output stream. } The Kryo pre-registering feature and the FST pre-registering feature have excellent performance. public String getStore() { If the versions of serialized and deserialized classes are different, the exception message java.io.InvalidClassException is returned, indicating that the VUID of the serialized class is inconsistent with that of deserialized classes. Thrift uses IDL to define the serialization class. All serialization frameworks provide good API usage except JDK Serializer. public final Object readObject() throws IOException, ClassNotFoundException. This has been a guide to Serialization in Java. FST supports the compatibility of new fields with old data streams using the @Version comment. Cross JVM Synchronization: different JVMs running on different machines and architectures can be synchronized. Your email address will not be published. Alibaba Cloud (in partnership with Whale Cloud) helps telcos build an all-in-one telecommunication and digital lifestyle platform based on DingTalk. The above code will produce the following result , Some important points related to the program above are provided below . Ice allows you to pass Java serializable objects directly as operation parameters or as fields of another data type. For example: The generated code for MyStruct contains a memberi of type int and a membero of type SomePackage.JavaClass: Similarly, the signature for op has parameters of type JavaClass and MyStruct for the in-parameters, and Ice.Holder for the out-parameter. Therefore, in terms of universality, Protobuf is very powerful. On the whole, FST has scalability, but it is still complicated to use. In the same way, ObjectInputStream class contains the method for object deserializing. Operating Principle and Implementation of Flink: Memory Management, Use Apache Arrow to Assist PySpark in Data Processing, Introduction to Java Virtual Machine (JVM) Performance Tuning, Data Types and Serialization: Flink Advanced Tutorials, Simple Introduction: Building Dubbo-go from Scratch and Dubbo Usage, Service Mesh Goes from "Trending" to "Predictable". Delete fields: To delete fields, note that the corresponding field or tag cannot be used in subsequent updates. public String getId() { Now its time to implement our class to test the process of serialization and deserialization. Therefore, they support the same Java data types and syntax. One of the main advantages of Hessian over other cross-language PRC frameworks is that it does not use IDL to define data and services. Instead, it defines services by self-description. Its serialization speed is ten times faster than JDK Serializable, but the byte size is only 1/3 the size of JDK Serializable. All new fields must be marked with @Version comments. Asynchronous Method Invocation (AMI) in Java. A desirable Setting Screen for Xamarin.forms, Top mistakes developers make when using Python for Big Data Analytics, Core Java: a beginning step to be best Core Java developer, Benefits of Custom Web Development for Business, Metaverse: A Technological Revolution To Look Forward To, Advancements in Deep Learning to Improve Diagnostics in Healthcare Industry, 5 Main Programming Languages you should Master as a Web Developer, How to Optimize Your Local SEO for More Visibility.
In addition, no cross-language practices of Kryo are found on the Internet. In order to get our output we will print toString() method of data value object class. Avro is a data serialization framework. io. public String toString() { The Java program should have a buffered approach for I/O operations to process Byte Stream. Direct serialization will result in the following exception: Runnable Lambda does not implement the interfaces of JDK Serializable. Set a default value for all fields. The above method can be used to serialize an Object. Users can use the serialization mechanism of Java by implementing java.io.Serializable or java.io.Externalizable. Avro supports the basic Java data types (null, Boolean, int, long, float, double, bytes, and string) and complex Java data types (Record, Enum, Array, Map, Union, and Fixed.). Serializable in java is a marker interface. }. Protobuf uses interface definition language (IDL) to define the schema description file. The following demo shows how to use FST for serialization. return client; Deserialization is its reverse process. The exception above occurs because serialVersionUID is not defined but generated automatically by JDK Serializable through the hash algorithm. Therefore, the results of serialization and deserialization are inconsistent. Next, use TSerializer and TDeserializer to serialize and deserialize objects. A stream is simply a sequence of data elements. The field name cannot be modified, but an alias can be added. return store; public void setPasswordKeys(String passwordKeys) { Java methods cannot be defined in serialized classes. In this article you learned about how to serialize and deserialize an object. Although JDK Serializable is exclusive for Java, its performance is not so good. Although some articles have mentioned that the cross-language use of Kryo is very complicated, no related implementation in other languages is found. The latest FST version is 2.56. dataObject.setId(hhhhh); Such a mechanism persists the object. All fields of the class must be serializable. Serialization in Java Example 2 : SerializationImplDemo.java. We create an Employee class to study some features, and the code for the same is provided below. Modify the code below to serialize Lambda expressions: Fast-serialization (FST) is a Java serialization framework that is fully compatible with the JDK serialization protocol. This article compares open-source serialization frameworks in the industry by the universality, usability, scalability, performance, and supports for Java data types and syntax. Data Stream Data Stream allows to read-write primitive data types and used to perform binary I/O operations on primitive data types. public void close() throws IOException {}. Protobuf does not support defining Java methods because it uses IDL to define schemas. Therefore, cross-language serialization and deserialization are not supported. It is a sub-project of Apache Hadoop and a data serialization framework developed by Doug Cutting while he was in charge of Hadoop. which well be covering in our next article. Perform the same serialization operation on the test sample using Protobuf. Java Data types supported by the serialization frameworks: Note: The collection class tests cover most corresponding implementation classes.
It only needs to implement the Serializable interface for serialized data. Both the classes ObjectInputStream and ObjectOutputStream are high-level streams and extend java.io.InputStream and java.io.OutputStream. Hessian is often used as a serialization framework because it supports cross-language and efficient binary serialization protocol. store : Programming Concepts In ObjectInputStream class we call the readObject() method which will carry out the actual deserialization. public String getPasswordKeys() { It shows how Protobuf is the best because it supports multiple programming languages. JDK Serializable is a serialization framework of Java. If a class object is to be serialized, then one needs to implement the java.io.Serializable interface. Serialization in Java is implemented by the two classesObjectInputStreamandObjectOutputStream. The deserialization method retrieves the object from a stream and deserializes the same. However, there are different serialization methods to serialize an object such as Serialization with Inheritance, Serialization with Aggregation, Serialization with static data number, Serialization with array or collection etc. JDK Serializable uses serialVersionUID to control the version of a serialized class. Kryo provides rich and flexible configurations, such as serializer customization and default serializer setting, but they are difficult to use. You may also look at the following article to learn more , Java Training (40 Courses, 29 Projects, 4 Quizzes). In terms of usability, FST is much better than JDK Serializable. Kryo is a fast and effective Java binary serialization framework. Once the object is serialized into written into a file, it can be read from the file and deserialized which means that the type of information and bytes that represent the object can be utilized to create object in the memory. The following demo shows encoding and decoding using JDK Serializable: JDK Serializable is a built-in serialization framework of Java. As Hessian uses Java self-description to serialize classes, the native data types, collection classes, custom classes, and enumeration types of Java are mostly supported (SynchronousQueue is not supported.) } Thrift is similar to Protobuf in terms of usability. Protobuf consumes less time in serialization than Thrift, while Thrift is better in deserialization. During deSerialize method we open the file in read mode using FileInputStream class and pass the object to BufferedInputStream class constructor. By doing so, JDK Serializable can support field extension. One FSTConfiguration can be called by multiple threads. This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy. Later, Facebook made Thrift open-source to Apache.
What type of CPU was used for executing the benchmarks? dataObject.setStore(Programming store); By signing up, you agree to our Terms of Use and Privacy Policy. The implementation of serialization interfaces means only the class can be serialized or deserialized. Deep Copy: If an exactreplica of an Object needs to be created and writing a specialized clone class is too much hard work, then only serializing the object and then de-serializing it to another object will achieve the goal. passwordKeys : null. (2) Use the compiler of Thrift to generate Java code: (3) Use TSerializer and TDeserializer for encoding and decoding: Similar to Protobuf, Thrift also uses IDL to define the description file. Lets understand the need for serialization in our concluding remarks. The class must implement a serializable interface. The encoding and decoding demo above is not user-friendly.
The byte size after serialization is 120 because the identity of the serialized class is a number instead of the class name. The class ObjectOutputStream, a serialization class mentioned in the above section, contains several writing methods for writing various data types, but one method is the most popular. The following table compares the universality of different serialization frameworks. This article compares open-source serialization frameworks in the industry by the universality, usability, scalability, performance, and supports for Java data types and syntax. The try/catch block above tries to catch a ClassNotFoundException. The following table lists the time consumption: Avro needs to use supported data types to write schema information. The following test sample will also be used for all other frameworks. A low-code development platform to make work easier, Help enterprises build high-quality, stable mobile apps. When this program is done with executing, a file named employee.ser would be created. Add fields: To add fields, make sure that the new fields have corresponding default values to interact with the old code. To make an object serializable we use java.io.Serializable interface.
Because of the same, the deserialized Employee SSN field object is 0. The object is then passed to the constructor class ObjectInputStream while instantiating. 3. transient private String id; So, if the byte size after serialization is restricted, choose Kryo or Avro. public final Object readObject() throws IOException, ClassNotFoundException{}. } Therefore, to use Protobuf, users simply need to prepare the description file.
All Java classes generated from Slice definitions implement the java.io.Serializable interface. this.passwordKeys = passwordKeys; The following table shows the time consumption of serialization and deserialization. @Override FST has supported Android since version 2.17. The scalability of Protobuf is the most convenient and natural. Use FST to serialize the test sample using JDK Serializable. Java Serialization API contains methods for serialization and deserialization. What is the difference between Augmented reality (AR) and Virtual Reality (VR) ? Protobuf has made a lot of efforts in scalability so it can support protocol extensions. Therefore, these functions cannot be tested. Above, we introduced serialization concepts and provided examples. It uses HTTP protocol to transmit data and supports binary serialization. Lets understand streams in computer systems before proceeding further. The following table displays the supports of Protobuf for data types: Note: List, Set, and Queue collection classes are defined and tested through the "repeated" modifier in Protobuf. Protocol Buffer (Protobuf) is a language-neutral, platform-independent, and scalable serialization framework. I/O operations can be performed for byte, char, boolean, short, int, long, float, double and strings efficiently and conveniently. However, for static languages, such as Java, avro-tools.jar is still necessary to compile and generate Java code. It relies on the underlying ASM library to generate bytecode, so it runs quickly. }, Serialization in Java Example 3 : DataObject.java, public class DataObject implements Serializable{. However, the current variety of serialization frameworks confuses people about the selection of serialization frameworks in different scenarios. Use Avro to serialize objects in the following three steps: (2) Use avro-tools.jar or Maven to compile and generate Java code: (3) Use BinaryEncoder and BinaryDecoder for encoding and decoding: Avro defines the data structure through schemas. This number will be compared to the other serialization frameworks. Calling serialization and deserialization methods. On the official website, Kryo is described as a Java binary serialization framework. The time consumed for serialization in FST is the shortest, while the time consumed for serialization and deserialization in Kryo are almost the same. Thank you for this excellent article, this is very informative. When deserialized the value of these transient fields will have the default value. The process of serialization is instance independent which means an object can be serialized on one platform and deserialized on an entirely different platform. The popular method to read an object in ObjectInputStream is: This method reads the stream of bytes and converts it back to an object which is called deserialization. Different data streams in the computer systems are: 1. Of course, your client and server code must have an implementation of JavaClass that derives from java.io.Serializable: You can implement this class in any way you see fit the Ice run time does not place any other requirements on the implementation. If a field is deleted after being added, the compatibility will be affected. Hessian 2.0 optimizes the serialization process, and its performance is significantly improved compared with Hessian 1.0. The default Kryo serializer FiledSerializer does not support field extension. Note: The corresponding Input.readxxx function must be used when using the Output.writeXxx function. This will read an object from the input stream. DataObject dataObject = new DataObject(); Apache Flink Community China - September 16, 2020. A class is made serializable by this process which looks like an Opt-In process. Thrift does not include short and char types, which are replaced with double and String types.
To perform serialization using Thrift, create the Thrift IDL file first and then compile the file to generate Java code. Although Hessian needs to implement the Serializable interface to serialize classes, it is not affected by serialVersionUID and supports field extension easily. The return value is again an object, so all that is needed is to cast it to a relevant data type. It is more complicated to write a Schema in Avro than in Thrift and Protobuf. Scalability is also one of the goals of Protobuf design. public void setStore(String store) { Persistence: If the state of operation is to be stored in a database, it is first serialized to a byte array and then stored in the database for retrieval at a later point in time. If the Serializer is implemented, users need to control the Version. Kryo aims to provide a serialization framework with fast serialization speed, small result size, and simple APIs. We protect those fields from getting saved during the process of serialization. In Java UNICODE system is followed to store characters as character stream. Avro does not need to generate code for dynamic languages. When we run our Serialization in Java program we can now observe the following output: client : Yolanda 2022 - EDUCBA. Using the keyword transient before any field of an object wont get serialized since transient objects are not eligible for serialization. } This will flush the current output stream. } The Kryo pre-registering feature and the FST pre-registering feature have excellent performance. public String getStore() { If the versions of serialized and deserialized classes are different, the exception message java.io.InvalidClassException is returned, indicating that the VUID of the serialized class is inconsistent with that of deserialized classes. Thrift uses IDL to define the serialization class. All serialization frameworks provide good API usage except JDK Serializer. public final Object readObject() throws IOException, ClassNotFoundException. This has been a guide to Serialization in Java. FST supports the compatibility of new fields with old data streams using the @Version comment. Cross JVM Synchronization: different JVMs running on different machines and architectures can be synchronized. Your email address will not be published. Alibaba Cloud (in partnership with Whale Cloud) helps telcos build an all-in-one telecommunication and digital lifestyle platform based on DingTalk. The above code will produce the following result , Some important points related to the program above are provided below . Ice allows you to pass Java serializable objects directly as operation parameters or as fields of another data type. For example: The generated code for MyStruct contains a memberi of type int and a membero of type SomePackage.JavaClass: Similarly, the signature for op has parameters of type JavaClass and MyStruct for the in-parameters, and Ice.Holder