java – HashMap序列化和反序列化更改

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我们正在使用内存数据网格(IMDG),我们有一个迁移工具.为了验证所有对象是否已成功迁移,我们从序列化版本计算对象的chucksum.

我们看到HashMap存在一些问题,我们将序列化它,但是当我们反序列化它时,校验和会发生变化.这是一个简单的测试用例：

@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：

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：

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,可以看到元素不在同一个地方：

{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.你知道是否有解决方案,或者我做错了什么？

谢谢！

迭戈

解决方法:

你没有做错任何事,只是不能用HashMap完成.在HashMap中,无法保证顺序.请改用TreeMap.

Hash table based implementation of the
Map interface. This implementation
provides all of the optional map
operations, and permits null values
and the null key. (The HashMap class
is roughly equivalent to Hashtable,
except that it is unsynchronized and
permits nulls.) This class makes no
guarantees as to the order of the map;
in particular, it does not guarantee
that the order will remain constant
over time.

资料来源：Hashmap

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