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    <p>You can't.</p> <p>As <a href="http://poi.apache.org/overview.html" rel="nofollow">explained on the POI Components page</a>, HSSF is for working with .xls files (OLE2 based), and XSSF/SXSSF is for working with .xlsx files (.xlsx)</p> <p>If you want to generate a .xls file, you'll have to use the HSSF UserModel. There is no streaming write support for HSSF, only <a href="http://poi.apache.org/spreadsheet/how-to.html#event_api" rel="nofollow">streaming read</a>.</p> <p>The .xls file format isn't so well suited to streaming write as .xlsx (more back/forwards references, offsets etc), so there's no streaming write support in HSSF. Just bump up your Java heap size, or switch to SXSSF for .xlsx, or just use something simple like CSV!</p> <p>.</p> <p><strong>Update</strong> If you need to test how much memory you ought to be giving to your system for writing with HSSF, or even XSSF, I'd suggest you try using the <a href="https://svn.apache.org/repos/asf/poi/trunk/src/examples/src/org/apache/poi/ss/examples/SSPerformanceTest.java" rel="nofollow">SSPerformanceTest example</a>, which can be run on the command line. Fire that up with all the jars, and a given heap size, and see if it completes. It takes arguments of the number of rows and columns, and the type of file to create. Using a nightly build and trying for a 40k row / 10 columns, I can get it to complete quickly in a 90mb heap:</p> <pre><code>$ java -Xmx90m -classpath poi-3.10-beta3-20131219.jar:poi-examples-3.10-beta3-20131219.jar:poi-ooxml-3.10-beta3-20131219.jar \ org.apache.poi.ss.examples.SSPerformanceTest HSSF 40000 10 1 Elapsed 1 seconds </code></pre>
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    1. POSaving SXSSF as .xls file
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    1. COI've set 2k ram heap for app but that wasn't enough. And there's no mode ram on the users pc, so i can't make heap size bigger. Then the only way is to use .xlsx?
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    2. COIf you're exporting huge amounts of data, you'll need to use .xlsx anyway as .xls has fairly small (by modern standards) limits on the number of rows and columns. If you're managing to use 2gb of memory, then you're almost certainly at those limits!
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    3. COi have ~40k rows and ~7-10 columns there. As far as i know, xls files can handle up to 65536, that might be enought for me
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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