public class SerializationUtils {
public static ByteArrayOutputStream serialize(Object object) throws IOException {
System.out.print("Serializing: " + object);
ByteArrayOutputStream bout = new ByteArrayOutputStream();
ObjectOutputStream out = new ObjectOutputStream(bout);
out.writeObject(object);
out.close();
return bout;
}
public static void deserialize(ByteArrayOutputStream bout) throws IOException,
ClassNotFoundException {
ByteArrayInputStream bin = new ByteArrayInputStream(bout.toByteArray());
ObjectInputStream in = new ObjectInputStream(bin);
Object readObject = in.readObject();
System.out.println(", deserialized: " + readObject);
}
}
Junit:
public class MySerializableClass implements Serializable {
}
public class MySerializationTest {
private String myJunitStringField = "hello";
static class MyStaticNestedSerializableClass implements Serializable {
public int getLength(String s) {
// Error: java: non-static variable this cannot be referenced from a static context
//System.out.println(MySerializationTest.this);// static nested class does not have reference to outer class
return s.length();
}
}
interface MySerializableFunction<T, R> extends Function<T, R>, Serializable {}
@Test
public void testSerialization() throws IOException, ClassNotFoundException {
deserialize(serialize(1)); // Serializing: 1, deserialized: 1
deserialize(serialize("aaa")); // Serializing: aaa, deserialized: aaa
deserialize(serialize(new MySerializableClass())); // Serializing: com.bawi.serialization.MySerializableClass@4520ebad, deserialized: com.bawi.serialization.MySerializableClass@4f933fd1
deserialize(serialize(new MyStaticNestedSerializableClass())); // Serializing: com.bawi.serialization.MySerializationTest$MyStaticNestedSerializableClass@4520ebad, deserialized: com.bawi.serialization.MySerializationTest$MyStaticNestedSerializableClass@4f933fd1
deserialize(serialize((MySerializableFunction<String, Integer>) s -> s.length()));
}
static class MyStaticNestedNonSerializableClass {} // missing implements Serializable
class MyInnerSerializableClass implements Serializable {
public int getLength(String s) {
System.out.println("myJunitStringField=" + myJunitStringField); // direct access to private outer class fields
System.out.println(MySerializationTest.this); // reference to enclosing instance of the outer class
return s.length();
}
}
@Test//(expected = java.io.NotSerializableException.class)
public void failWithNotSerializableException() throws IOException, ClassNotFoundException {
// NotSerializableException: com.bawi.serialization.MySerializationTest$MyStaticNestedNonSerializableClass
// deserialize(serialize(new MyStaticNestedNonSerializableClass()));
// inner (non static nested) class has reference to non-serializable outer class (junit com.bawi.serialization.MySerializationTest)
MyInnerSerializableClass myInnerSerializableClass = new MyInnerSerializableClass();
myInnerSerializableClass.getLength("a"); // myJunitStringField=hello
// com.bawi.serialization.MySerializationTest@1324409e
// java.io.NotSerializableException: com.bawi.serialization.MySerializationTest
// deserialize(serialize(myInnerSerializableClass));
class MyLocalSerializableClass implements Serializable {
@Override
public String toString() {
return MySerializationTest.this + "";
}
}
// java.io.NotSerializableException: com.bawi.serialization.MySerializationTest
// deserialize(serialize(new MyLocalSerializableClass()));
//anonymous is inner class: java.io.NotSerializableException: com.bawi.serialization.MySerializationTest
// deserialize(serialize(new Serializable(){
// @Override
// public String toString() {
// return MySerializationTest.this + "";
// }
// }));
// like local classes, anonymous classes have access to local variables of enclosing scope that are effectively final
// anonymous class definition (within {}) is an expression and must be part of the statement and end with semicolon
MyStaticNestedSerializableClass myAnonymousInnerSerializableClass = new MyStaticNestedSerializableClass() {
@Override
public int getLength(String s) {
System.out.println("myJunitStringField=" + myJunitStringField); // direct access to private outer class fields
System.out.println(MySerializationTest.this);
return s.length() + 2;
}
};
myAnonymousInnerSerializableClass.getLength("aa");
// java.io.NotSerializableException: com.bawi.serialization.MySerializationTest
// deserialize(serialize(myAnonymousInnerSerializableClass));
//java.io.NotSerializableException: com.bawi.serialization.MySerializationTest$$Lambda$1/1576861390
// deserialize(serialize((Function<String, Integer>) s -> s.length()));
}
}
If we make MySerializationTest implements Serializable then we will not get java.io.NotSerializableException: com.bawi.serialization.MySerializationTest
