Darryl Lyons' Blog: Using Java BufferedWriter to create CSV files

Please note, new blog at http://www.acheron.org/darryl/

Sunday, February 19, 2006Using Java BufferedWriter to create CSV files

Someone recently asked me to expand upon my previous post about generating CSV files, and in particular, to focus on the Java method. In my previous post, I concluded that using the Java BufferedWriter class is a much more scalable and stable solution than using the typical concatenate-and-write-once-done method.

Step by Step

There really isn't much to using Java to write to a file. Essentially, there are three steps, 1) create the Java class instances, 2) get the data and write to the buffer, and 3) close the output stream.

Firstly, we instantiate the FileWriter class (which writes to the file) and then the BufferedWriter class, passing the FileWriter instance as a parameter.

CFM:

<cfscript>
outputFile = getDirectoryFromPath(GetCurrentTemplatePath()) & "dump.csv";
oFileWriter = CreateObject("java","java.io.FileWriter").init(outputFile,JavaCast("boolean","true"));
oBufferedWriter = CreateObject("java","java.io.BufferedWriter").init(oFileWriter);
</cfscript>

Then, we create the column headers, and loop over the data (query in this case) and write it to the buffer. The Java class manages the size of the buffer internally, so when threshold is reached, it will write to the file.

CFM:

<cfset oBufferedWriter.write("LASTNAME,FIRSTNAME" & chr(13) & chr(10))>
<cfloop query="qData">
<cfset oBufferedWriter.write(chr(34) & lastname & chr(34) & ",")>
<cfset oBufferedWriter.write(chr(34) & firstname & chr(34) & chr(13) & chr(10))>
</cfloop>

Lastly, we need to close the output stream, otherwise the file will not be released.

CFM:

<cfset oBufferedWriter.close()>

Full code

CFM:

<cfscript>
outputFile = getDirectoryFromPath(GetCurrentTemplatePath()) & "dump.csv";
oFileWriter = CreateObject("java","java.io.FileWriter").init(outputFile,JavaCast("boolean","true"));
oBufferedWriter = CreateObject("java","java.io.BufferedWriter").init(oFileWriter);
</cfscript>
<cfquery datasource="cfartgallery" name="qData">
SELECT *
FROM artists
ORDER BY lastname, firstname
</cfquery>
<cftimer type="inline" label="Generate CSV">
<cfset oBufferedWriter.write("LASTNAME,FIRSTNAME" & chr(13) & chr(10))>
<cfloop query="qData">
<cfset oBufferedWriter.write(chr(34) & lastname & chr(34) & ",")>
<cfset oBufferedWriter.write(chr(34) & firstname & chr(34) & chr(13) & chr(10))>
</cfloop>
<cfset oBufferedWriter.close()>
</cftimer>

By Anonymous, at 2/19/2006 09:30:00 pm

This is a great post. Once you start getting into large file sizes(50MB+), using buffered readers and writters are a necessity in ColdFusion MX. JRun instances are usually set anywhere from 100MB to 512MB. ColdFusion MX Standalone can be set to around 1500MB. You can max out your JRun instance with ColdFusion by tring to use CFFILE on large files.

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