HashMap序列化和反序列化更改 [英] HashMap serialization and deserialization changes

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本文介绍了HashMap序列化和反序列化更改的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我们正在使用内存数据网格(IMDG),并且有一个迁移工具.为了验证是否成功迁移了所有对象,我们从其序列化版本中计算了对象的chucksum.

We are working with an in memory data grid (IMDG) and we have a migration tool. In order to verify that all the objects are migrated successfully, we calculate the chucksum of the objects from its serialized version.

我们看到了HashMap的一些问题,我们在其中进行了序列化,但是当我们对其进行反序列化时,校验和发生了变化.这是一个简单的测试用例:

We are seeing some problems with HashMap, where we serialize it, but when we deserialize it the checksum changes. Here is a simple test case:

@Test
public void testMapSerialization() throws IOException, ClassNotFoundException {
    TestClass tc1 = new TestClass();
    tc1.init();
    String checksum1 = SpaceObjectUtils.calculateChecksum(tc1);

    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ObjectOutput out = null;
    byte[] objBytes = null;
    out = new ObjectOutputStream(bos);
    out.writeObject(tc1);
    objBytes = bos.toByteArray();
    out.close();
    ByteArrayInputStream bis = new ByteArrayInputStream(objBytes);
    ObjectInputStream in = new ObjectInputStream(bis);
    TestClass tc2 = (TestClass) in.readObject();
    String checksum2 = SpaceObjectUtils.calculateChecksum(tc2);

    assertEquals(checksum1, checksum2);
}

TestClass看起来像这样:

The TestClass looks like this:

class TestClass implements Serializable {
    private static final long serialVersionUID = 5528034467300853270L;

    private Map<String, Object> map;

    public TestClass() {
    }

    public Map<String, Object> getMap() {
        return map;
    }

    public void setMap(Map<String, Object> map) {
        this.map = map;
    }

    public void init() {
        map = new HashMap<String, Object>();
        map.put("name", Integer.valueOf(4));
        map.put("type", Integer.valueOf(4));
        map.put("emails", new BigDecimal("43.3"));
        map.put("theme", "sdfsd");
        map.put("notes", Integer.valueOf(4));
        map.put("addresses", Integer.valueOf(4));
        map.put("additionalInformation", new BigDecimal("43.3"));
        map.put("accessKey", "sdfsd");
        map.put("accountId", Integer.valueOf(4));
        map.put("password", Integer.valueOf(4));
        map.put("domain", new BigDecimal("43.3"));
    }
}

这是计算校验和的方法:

And this is the method to calculate the checksum:

public static String calculateChecksum(Serializable obj) {
    if (obj == null) {
        throw new IllegalArgumentException("The object cannot be null");
    }
    MessageDigest digest = null;
    try {
        digest = MessageDigest.getInstance("MD5");
    } catch (java.security.NoSuchAlgorithmException nsae) {
        throw new IllegalStateException("Algorithm MD5 is not present", nsae);
    }
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ObjectOutput out = null;
    byte[] objBytes = null;
    try {
        out = new ObjectOutputStream(bos);
        out.writeObject(obj);
        objBytes = bos.toByteArray();
        out.close();
    } catch (IOException e) {
        throw new IllegalStateException(
                "There was a problem trying to get the byte stream of this object: " + obj.toString());
    }
    digest.update(objBytes);
    byte[] hash = digest.digest();
    StringBuilder hexString = new StringBuilder();
    for (int i = 0; i < hash.length; i++) {
        String hex = Integer.toHexString(0xFF & hash[i]);
        if (hex.length() == 1) {
            hexString.append('0');
        }
        hexString.append(hex);
    }
    return hexString.toString();
}

如果打印tc1和tc2的地图,您会发现元素不在同一位置:

If you print the maps of tc1 and tc2, you can see that the elements are not in the same place:

{accessKey=sdfsd, accountId=4, theme=sdfsd, name=4, domain=43.3, additionalInformation=43.3, emails=43.3, addresses=4, notes=4, type=4, password=4}
{accessKey=sdfsd, accountId=4, name=4, theme=sdfsd, domain=43.3, emails=43.3, additionalInformation=43.3, type=4, notes=4, addresses=4, password=4}

我希望能够序列化HashMap并在反序列化时获得相同的校验和.您知道是否有解决方案,或者我做错了什么?

I would like to be able to serialize the HashMap and get the same checksum when I deserialize it. Do you know if there is a solution or if I'm doing something wrong?

谢谢!

迭戈

推荐答案

您没有做错任何事情,只是使用HashMap无法做到.在HashMap中,不能保证顺序.使用 TreeMap .

You are doing nothing wrong, it just can't be done with a HashMap. In a HashMap, order is not guaranteed. Use a TreeMap instead.

基于哈希表的实现地图界面.这个实现提供所有可选地图操作,并允许空值和空键.(HashMap类大致相当于Hashtable,除了它是不同步的允许为空.)此类不允许保证地图的顺序;特别是,它不能保证顺序将保持不变随着时间的流逝.

来源: 哈希图

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