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public abstract class GenericServlet implements Servlet, ServletConfig, Serializable {

// abstract method

abstract void service(ServletRequest req, ServletResponse res);

void init() {

// Its implementation

}

// other method related to Servlet

}

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public class HttpServlet extends GenericServlet {

void service(ServletRequest req, ServletResponse res) {

// implementation

}

protected void doGet(HttpServletRequest req, HttpServletResponse resp) {

// Implementation

}

protected void doPost(HttpServletRequest req, HttpServletResponse resp) {

// Implementation

}

// some other methods related to HttpServlet

}

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public interface Externalizable extends Serializable {

void writeExternal(ObjectOutput out) throws IOException;

void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;

}

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public class Employee implements Externalizable {

int employeeId;

String employeeName;

@Override

public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {

employeeId = in.readInt();

employeeName = (String) in.readObject();

}

@Override

public void writeExternal(ObjectOutput out) throws IOException {

out.writeInt(employeeId);

out.writeObject(employeeName);

}

}