在log4j2 jdbcappender中设置日期时如何处理null？

Question

When I set null value in the date column I get "1900-01-01 00:00:00.000" value in my table and I am expecting NULL in that column. As this is handled properly in jdbc if I put like this

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>

Datatype of columns startdate and enddate is 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), "");

The same is for String with null value.

Answer 1

Inserting null

I don't think it's possible to get null into any column of any type using JDBCAppender with patterns like this.

This thread popped up a couple of years ago, followed by this Jira issue . None of it seems to have gotten any attention.

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.