279 lines
11 KiB
XML
279 lines
11 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!--
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====================================================================
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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====================================================================
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-->
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<!DOCTYPE faqs PUBLIC "-//APACHE//DTD FAQ V1.1//EN" "./dtd/faq-v11.dtd">
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<faqs title="Frequently Asked Questions">
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<faq>
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<question>
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My code uses some new feature, compiles fine but fails when live with a "MethodNotFoundException"
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</question>
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<answer>
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<p>You almost certainly have an older version of POI
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on your classpath. Quite a few runtimes and other packages
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will ship an older version of POI, so this is an easy problem
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to hit without your realising.</p>
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<p>The best way to identify the offending earlier jar file is
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with a few lines of java. These will load one of the core POI
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classes, and report where it came from.</p>
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<source>
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ClassLoader classloader =
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org.apache.poi.poifs.filesystem.POIFSFileSystem.class.getClassLoader();
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URL res = classloader.getResource(
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"org/apache/poi/poifs/filesystem/POIFSFileSystem.class");
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String path = res.getPath();
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System.out.println("Core POI came from " + path);
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</source>
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</answer>
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</faq>
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<faq>
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<question>
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My code uses the scratchpad, compiles fine but fails to run with a "MethodNotFoundException"
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</question>
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<answer>
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<p>You almost certainly have an older version earlier on your
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classpath. See the prior answer.</p>
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</answer>
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</faq>
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<faq>
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<question>
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Why is reading a simple sheet taking so long?
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</question>
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<answer>
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<p>You've probably enabled logging. Logging is intended only for
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autopsy style debugging. Having it enabled will reduce performance
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by a factor of at least 100. Logging is helpful for understanding
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why POI can't read some file or developing POI itself. Important
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errors are thrown as exceptions, which means you probably don't need
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logging.</p>
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</answer>
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</faq>
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<faq>
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<question>
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What is the HSSF "eventmodel"?
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</question>
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<answer>
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<p>The SS eventmodel package is an API for reading Excel files without loading the whole spreadsheet into memory. It does
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require more knowledge on the part of the user, but reduces memory consumption by more than
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tenfold. It is based on the AWT event model in combination with SAX. If you need read-only
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access, this is the best way to do it.</p>
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</answer>
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</faq>
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<faq>
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<question>
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Why can't read the document I created using Star Office 5.1?
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</question>
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<answer>
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<p>Star Office 5.1 writes some records using the older BIFF standard. This causes some problems
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with POI which supports only BIFF8.</p>
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</answer>
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</faq>
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<faq>
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<question>
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Why am I getting an exception each time I attempt to read my spreadsheet?
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</question>
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<answer>
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<p>It's possible your spreadsheet contains a feature that is not currently supported by POI.
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If you encounter this then please create the simplest file that demonstrates the trouble and submit it to
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<link href="http://issues.apache.org/bugzilla/buglist.cgi?product=POI">Bugzilla.</link></p>
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</answer>
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</faq>
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<faq>
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<question>
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How do you tell if a spreadsheet cell contains a date?
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</question>
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<answer>
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<p>Excel stores dates as numbers therefore the only way to determine if a cell is
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actually stored as a date is to look at the formatting. There is a helper method
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in HSSFDateUtil that checks for this.
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Thanks to Jason Hoffman for providing the solution.</p>
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<source>
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case HSSFCell.CELL_TYPE_NUMERIC:
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double d = cell.getNumericCellValue();
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// test if a date!
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if (HSSFDateUtil.isCellDateFormatted(cell)) {
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// format in form of M/D/YY
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cal.setTime(HSSFDateUtil.getJavaDate(d));
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cellText =
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(String.valueOf(cal.get(Calendar.YEAR))).substring(2);
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cellText = cal.get(Calendar.MONTH)+1 + "/" +
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cal.get(Calendar.DAY_OF_MONTH) + "/" +
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cellText;
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}
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</source>
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</answer>
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</faq>
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<faq>
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<question>
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I'm trying to stream an XLS file from a servlet and I'm having some trouble. What's the problem?
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</question>
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<answer>
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<p>
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The problem usually manifests itself as the junk characters being shown on
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screen. The problem persists even though you have set the correct mime type.
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</p>
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<p>
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The short answer is, don't depend on IE to display a binary file type properly if you stream it via a
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servlet. Every minor version of IE has different bugs on this issue.
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</p>
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<p>
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The problem in most versions of IE is that it does not use the mime type on
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the HTTP response to determine the file type; rather it uses the file extension
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on the request. Thus you might want to add a
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<strong>.xls</strong> to your request
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string. For example
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<em>http://yourserver.com/myServelet.xls?param1=xx</em>. This is
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easily accomplished through URL mapping in any servlet container. Sometimes
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a request like
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<em>http://yourserver.com/myServelet?param1=xx&dummy=file.xls</em> is also
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known to work.
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</p>
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<p>
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To guarantee opening the file properly in Excel from IE, write out your file to a
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temporary file under your web root from your servelet. Then send an http response
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to the browser to do a client side redirection to your temp file. (Note that using a
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server side redirect using RequestDispatcher will not be effective in this case)
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</p>
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<p>
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Note also that when you request a document that is opened with an
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external handler, IE sometimes makes two requests to the webserver. So if your
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generating process is heavy, it makes sense to write out to a temporary file, so that multiple
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requests happen for a static file.
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</p>
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<p>
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None of this is particular to Excel. The same problem arises when you try to
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generate any binary file dynamically to an IE client. For example, if you generate
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pdf files using
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<link href="http://xml.apache.org/fop">FOP</link>, you will come across many of the same issues.
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</p>
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<!-- Thanks to Avik for the answer -->
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</answer>
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</faq>
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<faq>
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<question>
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I want to set a cell format (Data format of a cell) of a excel sheet as ###,###,###.#### or ###,###,###.0000. Is it possible using POI ?
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</question>
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<answer>
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<p>
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Yes. You first need to get a DataFormat object from the workbook and call getFormat with the desired format. Some examples are <link href="spreadsheet/quick-guide.html#DataFormats">here</link>.
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</p>
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</answer>
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</faq>
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<faq>
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<question>
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I want to set a cell format (Data format of a cell) of a excel sheet as text. Is it possible using POI ?
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</question>
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<answer>
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<p>
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Yes. This is a built-in format for excel that you can get from DataFormat object using the format string "@". Also, the string "text" will alias this format.
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</p>
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</answer>
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</faq>
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<faq>
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<question>
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How do I add a border around a merged cell?
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</question>
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<answer>
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<p>Add blank cells around where the cells normally would have been and set the borders individually for each cell.
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We will probably enhance HSSF in the future to make this process easier.</p>
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</answer>
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</faq>
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<faq>
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<question>
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I am using styles when creating a workbook in POI, but Excel refuses to open the file, complaining about "Too Many Styles".
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</question>
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<answer>
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<p>You just create the styles OUTSIDE of the loop in which you create cells.</p>
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<p>GOOD:</p>
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<source>
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HSSFWorkbook wb = new HSSFWorkbook();
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HSSFSheet sheet = wb.createSheet("new sheet");
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HSSFRow row = null;
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// Aqua background
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HSSFCellStyle style = wb.createCellStyle();
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style.setFillBackgroundColor(HSSFColor.AQUA.index);
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style.setFillPattern(HSSFCellStyle.BIG_SPOTS);
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HSSFCell cell = row.createCell((short) 1);
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cell.setCellValue("X");
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cell.setCellStyle(style);
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// Orange "foreground",
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// foreground being the fill foreground not the font color.
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style = wb.createCellStyle();
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style.setFillForegroundColor(HSSFColor.ORANGE.index);
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style.setFillPattern(HSSFCellStyle.SOLID_FOREGROUND);
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for (int x = 0; x < 1000; x++) {
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// Create a row and put some cells in it. Rows are 0 based.
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row = sheet.createRow((short) k);
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for (int y = 0; y < 100; y++) {
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cell = row.createCell((short) k);
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cell.setCellValue("X");
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cell.setCellStyle(style);
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}
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}
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// Write the output to a file
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FileOutputStream fileOut = new FileOutputStream("workbook.xls");
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wb.write(fileOut);
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fileOut.close();
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</source>
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<p>BAD:</p>
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<source>
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HSSFWorkbook wb = new HSSFWorkbook();
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HSSFSheet sheet = wb.createSheet("new sheet");
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HSSFRow row = null;
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for (int x = 0; x < 1000; x++) {
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// Aqua background
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HSSFCellStyle style = wb.createCellStyle();
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style.setFillBackgroundColor(HSSFColor.AQUA.index);
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style.setFillPattern(HSSFCellStyle.BIG_SPOTS);
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HSSFCell cell = row.createCell((short) 1);
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cell.setCellValue("X");
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cell.setCellStyle(style);
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// Orange "foreground",
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// foreground being the fill foreground not the font color.
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style = wb.createCellStyle();
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style.setFillForegroundColor(HSSFColor.ORANGE.index);
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style.setFillPattern(HSSFCellStyle.SOLID_FOREGROUND);
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// Create a row and put some cells in it. Rows are 0 based.
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row = sheet.createRow((short) k);
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for (int y = 0; y < 100; y++) {
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cell = row.createCell((short) k);
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cell.setCellValue("X");
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cell.setCellStyle(style);
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}
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}
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// Write the output to a file
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FileOutputStream fileOut = new FileOutputStream("workbook.xls");
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wb.write(fileOut);
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fileOut.close();
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</source>
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</answer>
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</faq>
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</faqs>
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