How to get the MD5 checksum for a file

MD5 Hashsums are use to confirm the integrity of files. That is especially important when very large files are downloaded or moved from one location to another. To check the integrity of a file, its corresponding MD5 file can be downloaded and compared to the MD5 created locally on the file downloaded.


The program below can be used to create the MD5 hash for a file using the Apache Commons Codec lib:



The Windows program "md5sums" creates MD5 hashes.

In Unix, the BSD program "md5sum" creates MD5 hashes.


Reference
http://www.rgagnon.com/javadetails/java-0416.html

http://commons.apache.org/codec/

http://www.pc-tools.net/win32/md5sums/

Reading a file into a Java String

Comparing Java Date and Oracle Timestamp

Oracle 9.2 through 10.2 jdbc drivers causes java.util.Date to be mapped to java.sql.Date which does not include time information. Hence a direct comparison of a Java Date object to an Oracle Timestamp column like below will throw database errors

new java.sql.Date( .getTime() )

ORA-00932: inconsistent datatypes: expected TIMESTAMP got NUMBER


To be able to compare an Oracle Timestamp to a Java Date object, follow the steps below:


Step 1: Convert the Java Date to a String

Example:

Step 2: Use the String value in the SQL and use Oracle to_date() to convert it into Oracle date

Example:


Step 3: Cast the Oracle date into an Oracle timestamp
Example:


Reference
Oracle JDBC FAQ

Java Snippets on Date and Timestamp

Creating a Java Timestamp object


Convert String to Date


Converting java.util.Date to java.sql.Date 

The difference between both these date formats is the extra millisecond in java.sql.date

java.util.date ---------->dd mm yyyy hh:mm:ss

java.sql.date----------->dd mm yyyy hh:mm:ss: ms

The conversion is simple


Setting Date fields in the database using PreparedStatement
While setting a date using PreparedStatement, using setDate strips out the Time value. If you need the time field to be retained, use PreparedStatement setTime instead.


Getting Date fields from the database using ResultSet
While retrieving the Date value from the database, using getDate on ResultSet normally strips out the Time Value. To preserve the time fields, use ResultSet getTimeStamp instead.

CLOB's and Java Spring Framework

A CLOB (Character Large Object) is an Oracle data type  that can hold up to 4 GB of data. CLOB's are handy for storing large text since a VARCHAR has a maximum limit of 4000-bytes.


Here is an example of how to create a table with a CLOB:


Some common operations on CLOB's:

Writing to a CLOB:


Substr:




Finding the length of a CLOB:



Some caveats when dealing with LOB's:

• LOBs are not allowed in GROUP BY, ORDER BY, SELECT DISTINCT, aggregates and JOINS
• You cannot alter a table to add a CLOB column after creation. CLOB's have to be created at table creation time
• The Oracle SQL parser can only handle string literals up to 4000 characters in length

Dealing with CLOB’s in Java using Spring Framework:

The code below shows the basic parts of how to read and write to a CLOB using Spring 2.x.




There are also other options like using a MappingSqlQuery to read from the CLOB.




Reference:
Short examples from ASKTOM

Handling CLOBs - Made easy with Oracle JDBC