How To Serialize Java Object
- How To Serialize Java Object To File
- How To Serialize Java Object To Byte Array
- How To Serialize A Java Object
- How To Save A Serialized Java Object
- Java Serializable Example
- Java Tutorial
- Java Object Oriented
Java provides a mechanism, called object serialization where an object can be represented as a sequence of bytes that includes the object's data as well as information about the object's type and the types of data stored in the object. Jun 07, 2018 Kryo is a Java Object Serialization Framework. Because it is faster and more efficient than Java’s native serialization, it is widely used, for instance, in Spark and Flink which process the.
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Java provides a mechanism, called object serialization where an object can be represented as a sequence of bytes that includes the object's data as well as information about the object's type and the types of data stored in the object.
After a serialized object has been written into a file, it can be read from the file and deserialized that is, the type information and bytes that represent the object and its data can be used to recreate the object in memory.
Most impressive is that the entire process is JVM independent, meaning an object can be serialized on one platform and deserialized on an entirely different platform.
Classes ObjectInputStream and ObjectOutputStream are high-level streams that contain the methods for serializing and deserializing an object.
The ObjectOutputStream class contains many write methods for writing various data types, but one method in particular stands out −
The above method serializes an Object and sends it to the output stream. Similarly, the ObjectInputStream class contains the following method for deserializing an object −
This method retrieves the next Object out of the stream and deserializes it. The return value is Object, so you will need to cast it to its appropriate data type.
To demonstrate how serialization works in Java, I am going to use the Employee class that we discussed early on in the book. Suppose that we have the following Employee class, which implements the Serializable interface −
Example
Notice that for a class to be serialized successfully, two conditions must be met −
The class must implement the java.io.Serializable interface.
All of the fields in the class must be serializable. If a field is not serializable, it must be marked transient.
If you are curious to know if a Java Standard Class is serializable or not, check the documentation for the class. The test is simple: If the class implements java.io.Serializable, then it is serializable; otherwise, it's not.
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Serializing an Object
The ObjectOutputStream class is used to serialize an Object. The following SerializeDemo program instantiates an Employee object and serializes it to a file.
When the program is done executing, a file named employee.ser is created. The program does not generate any output, but study the code and try to determine what the program is doing.
Note − When serializing an object to a file, the standard convention in Java is to give the file a .ser extension.
Example
Deserializing an Object
The following DeserializeDemo program deserializes the Employee object created in the SerializeDemo program. Study the program and try to determine its output −
Example
This will produce the following result −
Output
Here are following important points to be noted −
The try/catch block tries to catch a ClassNotFoundException, which is declared by the readObject() method. For a JVM to be able to deserialize an object, it must be able to find the bytecode for the class. If the JVM can't find a class during the deserialization of an object, it throws a ClassNotFoundException.
Notice that the return value of readObject() is cast to an Employee reference.
The value of the SSN field was 11122333 when the object was serialized, but because the field is transient, this value was not sent to the output stream. The SSN field of the deserialized Employee object is 0.
I am able to serialize an object into a file and then restore it again as is shown in the next code snippet. I would like to serialize the object into a string and store into a database instead. Can anyone help me?
How To Serialize Java Object To File
casperOne13 Answers
Sergio:
You should use BLOB. It is pretty straighforward with JDBC.
The problem with the second code you posted is the encoding. You should additionally encode the bytes to make sure none of them fails.
If you still want to write it down into a String you can encode the bytes using java.util.Base64.
Still you should use CLOB as data type because you don't know how long the serialized data is going to be.
Here is a sample of how to use it.
Output:
NOTE: for Java 7 and earlier you can see the original answer here
How To Serialize Java Object To Byte Array
OscarRyzHow about writing the data to a ByteArrayOutputStream instead of a FileOutputStream?
Otherwise, you could serialize the object using XMLEncoder, persist the XML, then deserialize via XMLDecoder.
Outlaw ProgrammerOutlaw ProgrammerThanks for great and quick replies. I will gives some up votes inmediately to acknowledge your help. I have coded the best solution in my opinion based on your answers.
Note i did not considered using JSON because is less efficient.
Note: I will considered your advice about not storing serialized object as strings in the database but byte[] instead.
Sergio del AmoSergio del AmoXStream provides a simple utility for serializing/deserializing to/from XML, and it's very quick. Storing XML CLOBs rather than binary BLOBS is going to be less fragile, not to mention more readable.
skaffmanskaffmanIf you're storing an object as binary data in the database, then you really should use a BLOB datatype. The database is able to store it more efficiently, and you don't have to worry about encodings and the like. JDBC provides methods for creating and retrieving blobs in terms of streams. Use Java 6 if you can, it made some additions to the JDBC API that make dealing with blobs a whole lot easier.
If you absolutely need to store the data as a String, I would recommend XStream for XML-based storage (much easier than XMLEncoder), but alternative object representations might be just as useful (e.g. JSON). Your approach depends on why you actually need to store the object in this way.
Java8 approach, converting Object from/to String, inspired by answer from OscarRyz. For de-/encoding, java.util.Base64 is required and used.
Markus SchulteMarkus SchulteTake a look at the java.sql.PreparedStatement class, specifically the function
Then take a look at the java.sql.ResultSet class, specifically the function
How To Serialize A Java Object
Keep in mind that if you are serializing an object into a database, and then you change the object in your code in a new version, the deserialization process can easily fail because your object's signature changed. I once made this mistake with storing a custom Preferences serialized and then making a change to the Preferences definition. Suddenly I couldn't read any of the previously serialized information.
You might be better off writing clunky per property columns in a table and composing and decomposing the object in this manner instead, to avoid this issue with object versions and deserialization. Or writing the properties into a hashmap of some sort, like a java.util.Properties object, and then serializing the properties object which is extremely unlikely to change.
JoshJoshHow To Save A Serialized Java Object
The serialised stream is just a sequence of bytes (octets). So the question is how to convert a sequence of bytes to a String, and back again. Further it needs to use a limited set of character codes if it is going to be stored in a database.
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The obvious solution to the problem is to change the field to a binary LOB. If you want to stick with a characer LOB, then you'll need to encode in some scheme such as base64, hex or uu.
Tom Hawtin - tacklineJava Serializable Example
Tom Hawtin - tacklineYou can use the build in classes sun.misc.Base64Decoder and sun.misc.Base64Encoder to convert the binary data of the serialize to a string. You das not need additional classes because it are build in.