java - 为什么 ObjectOutputStream 和 ObjectInputStream 抛出 EOFException 的这种奇怪行为？

Question

我编写了一个自定义序列化/反序列化逻辑来保存一些数据，因为 Java 默认序列化结果是时间和内存都非常昂贵。为此，我为需要持久化的类编写了 readObject(ObjectInput in) 和 writeObject(ObjectOutput out) 方法。但是我注意到，如果我不在 writeObject(ObjectOutput out) 方法中使用任何 out.writeObject(obj)，那么它总是会抛出 EOFException。

考虑以下示例:

数据.java

public class Data implements BaseData {

private String messageUID;
private String rawData;
private String data;
private Long type;
private Boolean processed = false;
private String processedMessage;
private String processedDetaildMessage;

// getter setter

public void readObject(ObjectInput in) throws IOException, ClassNotFoundException {
    messageUID = in.readUTF();
    rawData = in.readUTF();
    data = in.readUTF();
    type = in.readLong();
    processed = in.readBoolean();
    if (processed) {
        processedMessage = in.readUTF();
        processedDetaildMessage = in.readUTF();
    }
}

public void writeObject(ObjectOutput out) throws IOException {
    out.writeUTF(messageUID);
    out.writeUTF(rawData);
    out.writeUTF(data);
    out.writeLong(type);
    out.writeBoolean(processed);
    if (processed) {
        out.writeUTF(processedMessage);
        String tempDetailsMessage[] = processedDetaildMessage.split(" more");
        out.writeUTF(tempDetailsMessage[tempDetailsMessage.length - 1]);
    }
}

然而，每当我使用上面的代码时，out 流总是在末尾缺少一些信息(来自 processedDetaildMessage 字段)并且我得到 EOFException从 in 中读取它时，下面的堆栈跟踪(Data.java 第 216 行是 processedDetaildMessage = in.readUTF())；

java.io.EOFException
    at java.io.ObjectInputStream$BlockDataInputStream.readByte(ObjectInputStream.java:2766)
    at java.io.ObjectInputStream$BlockDataInputStream.readUTFChar(ObjectInputStream.java:3158)
    at java.io.ObjectInputStream$BlockDataInputStream.readUTFBody(ObjectInputStream.java:3055)
    at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:2864)
    at java.io.ObjectInputStream.readUTF(ObjectInputStream.java:1072)
    at com.smartstream.common.Data.readObject(Data.java:216)
    at com.smartstream.common.PerformanceTest.getObjectFromBytes(PerformanceTest.java:168)
    at com.smartstream.common.PerformanceTest.access$0(PerformanceTest.java:160)
    at com.smartstream.common.PerformanceTest$1.mapRow(PerformanceTest.java:119)
    at com.smartstream.common.PerformanceTest$1.mapRow(PerformanceTest.java:1)
    at org.springframework.jdbc.core.RowMapperResultSetExtractor.extractData(RowMapperResultSetExtractor.java:92)
    at org.springframework.jdbc.core.RowMapperResultSetExtractor.extractData(RowMapperResultSetExtractor.java:60)
    at org.springframework.jdbc.core.JdbcTemplate$1.doInPreparedStatement(JdbcTemplate.java:651)
    at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:589)
    at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:639)
    at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:668)
    at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:676)
    at org.springframework.jdbc.core.JdbcTemplate.queryForObject(JdbcTemplate.java:731)
    at com.smartstream.common.PerformanceTest.readFromDb(PerformanceTest.java:109)
    at com.smartstream.common.PerformanceTest.main(PerformanceTest.java:66)

所以我虽然在写完所有必填字段后会在末尾放置一些额外的字节信息，但不会读取它们，这样我在读取时就不会到达文件末尾。我尝试了所有这些 out.writeByte(-1)、out.writeInt(-1)、out.writeLong(2342343l)、out.writeUTF("END_OF_STREAM") 但这些没有区别。最后我做了这个 out.writeObject(new String("END_OF_STREAM")) 并且它工作正常。如果没有使用 writeObject() 方法写入信息，有人可以解释为什么输出流会遗漏一些信息。下面是我如何读写流；

private byte[] getObjectAsBytes(Data data) {
    byte[] byteArray = null;
    ByteArrayOutputStream bos = null;
    ObjectOutputStream oos = null;
    try {
        bos = new ByteArrayOutputStream();
        oos = new ObjectOutputStream(bos);
        // Use this for java default serialization
        // oos.writeObject(data);
        data.writeObject(oos);
        byteArray = bos.toByteArray();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (oos != null) {
            try {
                oos.flush();
                oos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    return byteArray;
}

private Data getObjectFromBytes(byte[] byteArray) {
    Data data = new Data();
    ByteArrayInputStream bais = null;
    ObjectInputStream ois = null;
    try {
        bais = new ByteArrayInputStream(byteArray);
        ois = new ObjectInputStream(bais);
        // Use this for java default serialization
        // data = (Data) ois.readObject();
        data.readObject(ois);
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } finally {
        if (ois != null) {
            try {
                ois.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    return data;
}

如果有人感兴趣，下面是流中写的内容；

使用原始代码保留数据(抛出 EOFException 和丢失的信息)(不要将堆栈跟踪与原始问题混淆此堆栈跟踪作为字段 processedDetailedMessage)

¬í---z-------3507319347632941385----FEEDER-----1437052314954 ---This is a random string---N---þ%J---!this is message of processed dataÛ
Caused by: java.sql.SQLException: ORA-01691: unable to extend lob segment TLM_DBO.SYS_LOB0000076335C00008$$ by 8192 in tablespace WIN_SL_TABLE
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:439)
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:395)
at oracle.jdbc.driver.T4C8Oall.processError(T4C8Oall.java:802)
at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:436)
at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:186)
at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:521)
at oracle.jdbc.driver.T4CPreparedStatement.doOall8(T4CPreparedStatement.java:205)
at oracle.jdbc.driver.T4CPreparedStatement.executeForRows(T4CPreparedStatement.java:1008)
at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1307)
at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(OraclePreparedStatement.java:3449)
at oracle.jdbc.driver.OraclePre

使用 writeObject 方法在末尾写入额外字符串后保留数据

¬í---z-------3507319347632941385----FEEDER-----1437052314954 ---This is a random string---N---þ%J---!this is message of processed dataÛ
Caused by: java.sql.SQLException: ORA-01691: unable to extend lob segment TLM_DBO.SYS_LOB0000076335C00008$$ by 8192 in tablespace WIN_SL_TABLE
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:439)
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:395)
at oracle.jdbc.driver.T4C8Oall.processError(T4C8Oall.java:802)
at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:436)
at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:186)
at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:521)
at oracle.jdbc.driver.T4CPreparedStatement.doOall8(T4CPreparedStatement.java:205)
at oracle.jdbc.driver.T4CPreparedStatement.executeForRows(T4CPreparedStatement.java:1008)
at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1307)
at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(OraclePreparedStatement.java:3449)
at oracle.jdbc.driver.OraclePrz-----NeparedStatement.execute(OraclePreparedStatement.java:3550)
at oracle.jdbc.driver.OraclePreparedStatementWrapper.execute(OraclePreparedStatementWrapper.java:1374)
at com.ibm.ws.rsadapter.jdbc.WSJdbcPreparedStatement.pmiExecute(WSJdbcPreparedStatement.java:975)
at com.ibm.ws.rsadapter.jdbc.WSJdbcPreparedStatement.execute(WSJdbcPreparedStatement.java:642)
at com.smartstream.control.engine.config.dao.jdbc.ProcessExecutionAuditDetailDao$1.doInPreparedStatement(ProcessExecutionAuditDetailDao.java:115)
at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:586)
... 23t 
END_OF_STREAM

PS ----代表不可读字节

Answer 1

您的持久化数据不完整，因为您在刷新 ObjectOutputStream 之前创建字节数组。在 getObjectAsBytes(Data) 中，在 finally block 之后移动 byteArray = bos.toByteArray(); 以使其工作。或者，该方法可以更简洁地编写如下(需要 Java 7+):

private byte[] getObjectAsBytes(Data data) {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    try (ObjectOutputStream oos = new ObjectOutputStream(bos)) {
        data.writeObject(oos);
    } catch (IOException e) {
        e.printStackTrace();
    }
    return bos.toByteArray();
}

我在自己的程序中测试了这两种方式，它们都可以防止抛出 EOFException。

至于为什么有一个 writeObject 是有效的，那是因为 underlying writeObject implementation在方法的开头和结尾切换 block 数据模式，changing the block data mode performs a drain它将所有数据写入底层 OutputStream，对于 ByteArrayOutputStream，这实际上与刷新相同。