Question

我尝试使用某些对象对ArrayList进行序列化和反序列化。第一次运行程序时，一切正常，但是下次运行时，则无效：

public class Test {

    private static final String FILE_NAME = "Objects.ser";

    public static void main(String[] args) {

        ArrayList<CustomObject> customObjects = getCustomObjects();
        System.out.println("CustomObjects count: "+customObjects.size());
        System.out.println("Adding 5 CustomObjects");
        Random rand = new Random();
        for(int i=0; i<5; i++){
            CustomObject obj = new CustomObject();
            obj.setIntValue(rand.nextInt());
            customObjects.add(obj);
        }
        System.out.println("CustomObjects count: "+customObjects.size());
        System.out.println("Save and load CustomObjects");
        saveCustomObjects(customObjects);
        customObjects = getCustomObjects();
        System.out.println("CustomObjects count: "+customObjects.size());
    }

    public static ArrayList<CustomObject> getCustomObjects(){
        try (
            FileInputStream fin = new FileInputStream(FILE_NAME);
            ObjectInputStream ois = new ObjectInputStream(fin);
        ){
            return (ArrayList<CustomObject>) ois.readObject();

        } catch (Exception ex) {
            return new ArrayList<>();
        }

    }

    public static void saveCustomObjects(ArrayList<CustomObject> strategies) {
        try(
            FileOutputStream fout = new FileOutputStream(FILE_NAME, true);
            ObjectOutputStream oos = new ObjectOutputStream(fout);
        ){
            oos.writeObject(strategies);
            //tried also with oos.flush();

        } catch (Exception ex) {

            ex.printStackTrace();
        }
    }
}
public class CustomObject implements Serializable{

    static final long serialVersionUID = 42L;

    private int intValue=0;
    private EnumTypes enumType=EnumTypes.ENUM_TYPE_ONE;

    public enum EnumTypes{
        ENUM_TYPE_ONE, ENUM_TYPE_TWO
    }

    public int getIntValue() {
        return intValue;
    }

    public void setIntValue(int intValue) {
        this.intValue = intValue;
    }

    public EnumTypes getEnumTypes() {
        return enumType;
    }

    public void setEnumTypes(EnumTypes enumTypes) {
        this.enumType = enumTypes;
    }

    @Override
    public int hashCode() {
        int hash = 3;
        hash = 97 * hash + this.intValue;
        hash = 97 * hash + Objects.hashCode(this.enumType);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final CustomObject other = (CustomObject) obj;
        if (this.intValue != other.intValue) {
            return false;
        }
        if (this.enumType != other.enumType) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "CustomObject{" + "intValue=" + intValue + ", enumTypes=" + enumType + '}';
    }
}

该应用程序首次运行的输出显示了所有与预期类似的内容：

CustomObjects count: 0
Adding 5 CustomObjects
CustomObjects count: 5
Save and load CustomObjects
CustomObjects count: 5

但是在下一次运行之后，输出看起来总是像带有序列化ArrayList中对象的文件无法被覆盖：

CustomObjects count: 5
Adding 5 CustomObjects
CustomObjects count: 10
Save and load CustomObjects
CustomObjects count: 5

我在Mac上的netbeans和控制台中进行了测试。有人知道问题出在哪里吗？

Answer 1

就是这样，什么也不会被覆盖，因为您在写入文件时明确选择了附加而不是覆盖：

new FileOutputStream(FILE_NAME, true);

因此，第一次运行不会读取任何内容，并将5个元素的列表附加到文件中。第二次运行读取唯一列表，并将另一个包含10个元素的列表追加到文件中。第三次运行读取文件中的第一个列表，并追加另一个包含10个元素的列表，依此类推。

删除第二个参数，或将其设置为false。

ArrayList的Java序列化/反序列化仅在首次执行程序时有效

1 个答案: