How to save a complex java object in a MySQL table
If you want to save complex java objects to MySQL you can serialize and save them as BLOB in a MySQL table.
For example you have an object “complexObject” from class “ComplexObject” and you want to save it in database.
The ComplexObject class must implements Serializable interface and you can serialize the objects like this:
ByteArrayOutputStream baos;
ObjectOutputStream out;
baos = new ByteArrayOutputStream();
try {
out = new ObjectOutputStream(baos);
out.writeObject(complexObject);
out.close();
} catch (IOException e) {
e.printStackTrace();
}
byte[] byteObject = baos.toByteArray();
to deserialize the object :
ByteArrayInputStream bais;
ObjectInputStream in;
try {
bais = new ByteArrayInputStream(byteObject);
in = new ObjectInputStream(bais);
complexObject = (ComplexObject) in.readObject();
in.close();
} catch (IOException ex) {
ex.printStackTrace();
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
The MySQL table looks like this:

CREATE TABLE myTable(

complexObject BLOB,…

);
If you use Hibernate and Annotation you declare the complexObject transient, and a byte[] byteObject that will be persisted:
@Entity
@Table(name = “myTable”)
SomeClass{
private byte[] byteObject;
private ComplexObject complexObject;

@Transient
public ComplexObject getComplexObject() {
return complexObject;
}
public void setComplexObject(ComplexObject complexObject) {
this.complexObject = complexObject;
ByteArrayOutputStream baos;
ObjectOutputStream out;
baos = new ByteArrayOutputStream();
try {
out = new ObjectOutputStream(baos);
out.writeObject(complexObject);
out.close();
} catch (IOException e) {
e.printStackTrace();
}
this.byteObject = baos.toByteArray();
}
@Column(columnDefinition = “blob”)
public byte[] getByteObject() {
return byteObject;
}
public void setByteObject(byte[] byteObject) {
ByteArrayInputStream bais;
ObjectInputStream in;
try {
bais = new ByteArrayInputStream(byteObject);
in = new ObjectInputStream(bais);
complexObject = (ComplexObject) in.readObject();
in.close();
} catch (IOException ex) {
ex.printStackTrace();
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
this.byteObject= byteObject;
}
}
Attention the table column must be BLOB, not varchar.
Because the ComplexObject is transient it will not be save in database, but the byteObject will be save.

4 responses to “Serializable java objects in MySQL

  1. hi i worked out in your code. but the foloowing error occured.
    How to solve it?

    20:41:32,129 [main] INFO Version : Hibernate Annotations 3.3.0.GA
    20:41:32,153 [main] INFO Environment : Hibernate 3.1
    20:41:32,160 [main] INFO Environment : hibernate.properties not found
    20:41:32,164 [main] INFO Environment : using CGLIB reflection optimizer
    20:41:32,166 [main] INFO Environment : using JDK 1.4 java.sql.Timestamp handling
    20:41:32,268 [main] INFO Configuration : configuring from resource: /hibernate.cfg.xml
    20:41:32,269 [main] INFO Configuration : Configuration resource: /hibernate.cfg.xml
    20:41:32,426 [main] INFO Configuration : Reading mappings from resource: org/jbpm/graph/action/Script.hbm.xml
    Exception in thread “main” java.lang.IllegalAccessError: tried to access field org.hibernate.cfg.Configuration.xmlHelper from class org.hibernate.cfg.AnnotationConfiguration
    at org.hibernate.cfg.AnnotationConfiguration.addInputStream(AnnotationConfiguration.java:712)
    at org.hibernate.cfg.Configuration.addResource(Configuration.java:481)
    at org.hibernate.cfg.AnnotationConfiguration.parseMappingElement(AnnotationConfiguration.java:581)
    at org.hibernate.cfg.Configuration.parseSessionFactory(Configuration.java:1411)
    at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1392)
    at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1368)
    at org.hibernate.cfg.Configuration.configure(Configuration.java:1288)
    at org.hibernate.cfg.Configuration.configure(Configuration.java:1274)
    at MainClass.main(MainClass.java:28)

  2. how to read stored files from blob column….,

    i am using hibernate java and mysql……….

    plz help me with some sample code

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