如何在log4j2 jdbcappender中设置日期时处理null？

Question

当我在日期列中设置空值时,我在表中得到"1900-01-01 00:00:00.000"值,我期望该列中为NULL.因为这样在jdbc中正确处理,如果我这样说

preparedStatement.setBindParam(Types.TIMESTAMP, 12, startdate);

log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="debug">

    <CustomLevels>
        <CustomLevel name="TESTLOG" intLevel="552" />
    </CustomLevels>

    <Appenders>

        <JDBC name="myAppender" tableName="MYTABLE">
            <DataSource jndiName="java:MyDataSource" />
            <Column name="ID" pattern="%X{ID}" isUnicode="false"/>
            <Column name="startdate" pattern="%X{startdate}" isUnicode="false"/>
            <Column name="enddate" pattern="%X{enddate}" isUnicode="false"/>
        </JDBC>

    </Appenders>

    <Loggers>
        <Root level="trace"  includeLocation="false">
            <AppenderRef ref="myAppender" level="TESTLOG" />
        </Root>
    </Loggers>

</Configuration>

列startdate和enddate的数据类型是datetime

ThreadContext.put("startdate", startdate != null ? startdate.toString() : null);
ThreadContext.put("enddate", a_reportEndDate != null ? enddate.toString() : null);
final Logger LOGGER = LogManager.getLogger();
LOGGER.log(Level.forName("TESTLOG", 552), "");

对于具有空值的String也是如此.

Answer 1

插入空值

我认为使用这样的模式不可能进入null任何类型的任何列。JDBCAppender

该帖子几年前出现，随后出现了Jira 问题。这些似乎都没有引起任何注意。

The short version is that a StringBuilder is used between pattern and prepared statement, and thus the INSERT always gets a non-null string, even if (in your example) null is the value in the ThreadContext. So it's possible to insert an empty string, or the string "null", but it doesn't appear to be possible to insert the value null.

January 1, 1900

When I run your example against a MySQL database, the insert fails up front, because MySQL doesn't know how to construct a DATETIME from an empty string.

I'm guessing you're using SQL Server, which will happily turn an empty string into 1900-01-01 00:00:00.000, because of course that's what you meant.

Regardless of the database you use, JDBCAppender is going to fill the INSERT statement with non-null strings. What happens from there will vary from DB to DB.

Why?

At first it may seem strange that the framework is changing your value (null) to another value (empty string). However, at its core, logging is about strings of text.

Yes, there's an appender that will write these strings to a database. And yes, your database can in turn coax those strings into types like DATETIME or INTEGER. But to any given appender, it's all really just about manipulating and outputting strings.

Possible work-around

If you really want to get null into the database using JDBCAppender, you may be able to write a trigger.

Final Observation

Not sure if this helps any, but I may as well present all my findings:

Using ColumnMapping instead of Column in your log4j config allows you to specify a class name. The presence (or absence) and value of this class name does change the value that is inserted into the database. For example, using SQL Server Express 2014:

<ColumnMapping name="startdate" pattern="%X{startdate}" type="java.sql.Timestamp"/>

Will cause the current date and time to be logged when startdate is null, instead of 1900-01-01. Using java.sql.Date instead will log the current date without time.