在Java中序列化并保存一个double []的ArrayList

Question

I want to serialize and save an arraylist that contains a double [] arraylist in java. Here is my code.

FileOutputStream fileOutputStream = null; 
ObjectOutputStream objectOutputStream = null; 
FileInputStream fileInputStream = null; 
ObjectInputStream objectInputStream = null; 

public void writeArrayListToFile(ArrayList<ArrayList<double []>> arraylist, String outputFilePath){

    System.out.println("Start saving the file at  : " + outputFilePath);

    try {
        fileOutputStream = new FileOutputStream(outputFilePath , true);
        objectOutputStream = new ObjectOutputStream(objectOutputStream);
        objectOutputStream.writeObject(arraylist);
        System.out.println("Arraylist Saved Successfully...");
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }       
}

But I get an error and following is the stack trace.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at java.io.ObjectOutputStream$BlockDataOutputStream.drain(Unknown Source) at java.io.ObjectOutputStream$BlockDataOutputStream.setBlockDataMode(Unknown Source) at java.io.ObjectOutputStream.(Unknown Source) at com.fyp.imur2.SaveArrayListToFile.writeArrayListToFile(SaveArrayListToFile.java:24) at com.fyp.imur2.JPanelJFreeChart.btnSaveGestureCollectionActionPerformed(JPanelJFreeChart.java:380) at com.fyp.imur2.JPanelJFreeChart.access$5(JPanelJFreeChart.java:375) at com.fyp.imur2.JPanelJFreeChart$6.actionPerformed(JPanelJFreeChart.java:166) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) at java.awt.Component.processMouseEvent(Unkn own Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$200(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doInt ersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)

Can someone help me to solve this issue? Any help would be appreciated. Thanks in advance.

Answer 1

在构造ObjectOutputStream的实例时需要传递fileOutputStream

objectOutputStream = new ObjectOutputStream(fileOutputStream);

Answer 2

on the line

objectOutputStream = new ObjectOutputStream(objectOutputStream);

You try to call the constructor with the objectOutputStream object, which is null. Looks like you meant to call it with fileOutputStream, like this:

objectOutputStream = new ObjectOutputStream(fileOutputStream);