Question

我正在构建一个处理Binary De / Serialization的类。方法open()会收到InputStream和OutputStream。这些是由另一个open()方法创建的，该方法接收路径作为参数。 InputStream实际上是ByteArrayInputStream。我已经做了一些测试来证明InputStream到达带有内容的open()方法 - 实际上是。但是当我尝试使用它设置ObjectInputStream时，它不起作用。没有抛出异常，但是当我尝试从中读取字节时，它总是给我-1。

BinaryStrategy类

public class BinaryStrategy implements SerializableStrategy{
  public BinaryStrategy(){
    try{
        open("products.ser");
    }catch(IOException ioe){

    }
  } 
  @Override
  public void open(InputStream input, OutputStream output) throws IOException  {
    try{
        this.ois = new ObjectInputStream(input);
    }catch(Exception ioe){
        System.out.println(ioe);
    }
    this.oos = new ObjectOutputStream(output);
  }
  @Override
  public void writeObject(fpt.com.Product obj) throws IOException {
    oos.writeObject(obj);
    oos.flush();
  }
  @Override
  public Product readObject() throws IOException {
    Product read = new Product();
    try{
        read.readExternal(ois);
    }catch(IOException | ClassNotFoundException exc){
        System.out.println(exc);
    }
    return read;
  }
}

interface SerializableStrategy（只是默认方法）

    default void open(Path path) throws IOException {
    if (path != null) {
        ByteArrayInputStream in = null;
        if (Files.exists(path)) {
            byte[] data = Files.readAllBytes(path);
            in = new ByteArrayInputStream(data);
        }
        OutputStream out = Files.newOutputStream(path);
        open(in, out);
    }

产品类

public class Product implements java.io.Externalizable {
    @Override
public void writeExternal(ObjectOutput out) throws IOException {
    out.writeLong(getId());
    out.writeObject(getName());
    out.writeObject(getPrice());
    out.writeObject(getQuantity());
}

@Override
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
    this.setId((Long)in.readLong());
    this.setName((String) in.readObject());
    this.setPrice((Double) in.readObject());
    this.setQuantity((Integer) in.readObject());
}

我必须对其进行个性化，因为属性为SimpleProperty s

在public void open(InputStream input, OutputStream output)，我尝试按照以下步骤进行测试：

    public void open(InputStream input, OutputStream output) throws IOException {
    try{
        System.out.println(input.available() + " " + input.read() + " " + input.read());
        //is gives me: 181 172 237
        //181 is the exact size of the file I have, so i think that the Output is ok
        //172 237 - just some chars that are in the file
        //I know that for now on it is going to give me an excepetion because
        // of the position of the index that is reading. I did it just to test
        this.ois = new ObjectInputStream(input);
    }catch(Exception ioe){
        System.out.println(ioe);
    }
    this.oos = new ObjectOutputStream(output);
}

然后另一个测试：

public void open(InputStream input, OutputStream output) throws IOException {
    try{
        this.ois = new ObjectInputStream(input);
        System.out.println(ois.available() + " " + ois.read());
        //here is where I am receiving -1 and 0 available bytes!
        //so something is going wrong right here.
        //i tried to just go on and try to read the object,
        //but I got a EOFException, in other words, -1.
    }catch(Exception ioe){
        System.out.println(ioe);
    }
    this.oos = new ObjectOutputStream(output);
}

Answer 1

请检查path表示的文件是否写入了java对象。
从ObjectInputStream API doc https://docs.oracle.com/javase/7/docs/api/java/io/ObjectInputStream.html

ObjectInputStream对先前使用ObjectOutputStream编写的基元数据和对象进行反序列化。

ObjectInputStream用于恢复先前序列化的对象。

如果您正在执行this.ois.readObject()，并且获得-1，则该文件可能不包含其中的对象。

更新：readObject返回一个对象，而不是int。如果您使用read中的ois方法，并且获得-1，则该文件为空。

此外，您的文件可能包含 -1 作为其内容;）

Answer 2

问题是我正在以错误的方式阅读ObjectInputStream。它就像：

read.readExternal(ois);

但正确的方法是：

read = (Product)ois.readObject();

由于我这样做的例外情况，我认为问题在于使用ObjectInputStream时构建ByteArrayInputStream。真是个大错！：d

感谢所有试图提供帮助的人。

Answer 3

ObjectInputStream，在内部使用BlockDataInputStream执行其读取操作。当您调用read时，这会读取一个数据块，而不仅仅是我们所期望的字节。它只读取一个字节，如果它是＆＃34;块＆＃34;

输出不是我所期望的。但是，如果你看一下ObjectInputStream.read()的代码，那就有道理了。

因此，在您的情况下，仅使用readObject来恢复您的对象是有意义的。状态。

再次见到你的代码......

class SimpleJava {

    public static void open(InputStream input, OutputStream output) throws IOException {

        try {
            ObjectInputStream ois = new ObjectInputStream(input);
            System.out.println(ois.available());// 0
            System.out.println(ois.available() + " " + ois.read() + " " + ois.read());// 0 -1 -1
            // Reads the object even if the available returned 0 
            // and ois.read() returned -1
            System.out.println("object:" + ois.readObject());// object:abcd
        }
        catch (Exception ioe) {
            ioe.printStackTrace();
        }
    }

    static void open(Path path) throws IOException {

        if (path != null) {
            ByteArrayInputStream in = null;
            if (Files.exists(path)) {
                byte[] data = Files.readAllBytes(path);
                in = new ByteArrayInputStream(data);
            }
            OutputStream out = Files.newOutputStream(path);
            open(in, out);
        }
    }

    public static void main(String[] args) throws Exception {

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(new File("/home/pradhan/temp.object")));
        oos.writeObject("abcd");//writes a string object for us to read later
        oos.close();
        //
        open(FileSystems.getDefault().getPath("/home/user/temp.object"));
    }
}

继承人的产出......

0
0 -1 -1
object:abcd

使用ByteArrayInputStream

3 个答案: