Java中的 ObjectInputStream enableResolveObject() 方法及示例

简介

在Java中，ObjectInputStream是用于读取Java对象的类。它是InputStream的子类，允许Java对象被读入InputStream并重新生成。enableResolveObject()方法是ObjectInputStream类中的一种方法，允许在读取对象时使用ObjectInputStream将相同对象的多个实例变成同一对象。

方法定义

protected void enableResolveObject(boolean enable);

方法参数

• enable：一个布尔值，指示是否启用了解析对象。

方法说明

该方法允许在读取对象时使用ObjectInputStream将相同对象的多个实例变成同一对象。如果启用了解析对象，则在读取对象时将调用resolveObject(Object obj)，并使用返回的对象替换从流中读取的对象。

例如，如果从流中读取了一个序列化的对象，并且该对象有一个字段引用另一个对象，而另一个对象已经早先被读入流中，则使用此方法将启用ObjectInputStream将此字段引用替换为此前读取的对象实例。

示例

public class Person implements Serializable {
    private String name;
    private transient Address address; // Address类实现了Serializable接口

    public Person(String name, Address address) {
        this.name = name;
        this.address = address;
    }

    private void writeObject(ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        out.writeObject(address.getStreet());
        out.writeObject(address.getCity());
        out.writeObject(address.getState());
        out.writeObject(address.getZipcode());
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        String street = (String) in.readObject();
        String city = (String) in.readObject();
        String state = (String) in.readObject();
        String zipcode = (String) in.readObject();
        address = new Address(street, city, state, zipcode);
    }

    private Object writeReplace() throws ObjectStreamException {
        return this;
    }

    private Object readResolve() throws ObjectStreamException {
        return this;
    }
}

public class Address implements Serializable {
    private String street;
    private String city;
    private String state;
    private String zipcode;

    public Address(String street, String city, String state, String zipcode) {
        this.street = street;
        this.city = city;
        this.state = state;
        this.zipcode = zipcode;
    }

    public String getStreet() {
        return street;
    }

    public String getCity() {
        return city;
    }

    public String getState() {
        return state;
    }

    public String getZipcode() {
        return zipcode;
    }
}

public class Main {
    public static void main(String[] args) throws Exception {
        Address address = new Address("123 Main St", "Anytown", "CA", "12345");
        Person person1 = new Person("John", address);
        Person person2 = new Person("Mary", address);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(person1);
        oos.writeObject(person2);
        oos.flush();
        byte[] bytes = baos.toByteArray();
        System.out.println("bytes.length=" + bytes.length);
        ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bytes));
        ois.enableResolveObject(true);
        Person readPerson1 = (Person) ois.readObject();
        Person readPerson2 = (Person) ois.readObject();
        ois.close();
        System.out.println("readPerson1.getName()=" + readPerson1.getName());
        System.out.println("readPerson2.getName()=" + readPerson2.getName());
        System.out.println("readPerson1.getAddress()=" + readPerson1.getAddress());
        System.out.println("readPerson2.getAddress()=" + readPerson2.getAddress());
    }
}

在上面这个例子中，我们将一个Address对象序列化为字节数组，并在两个Person对象中共享这个Address对象。当我们读取这两个Person对象时，enableResolveObject()方法允许ObjectInputStream将两个Person对象中的Address实例替换为同一个实例。我们还重载了Person类的writeReplace()和readResolve()方法，以确保序列化和反序列化过程中使用正确的Person对象。

总结

本文介绍了Java中的ObjectInputStream enableResolveObject()方法及其用法。它允许在读取对象时使用ObjectInputStream将相同对象的多个实例变成同一对象，从而提高性能和减小内存占用。在代码中，我们使用了一个完整的示例来演示如何使用此方法。