如何使用PDFBox将多个小型PDF合并为一个，而不会耗尽堆空间？

Finni McFinger 发表于 Dev

寻找麦芬格

我一直在尝试将多个较小的PDF（到目前为止，我使用的最大的6 MB）合并为一个PDF。每当我尝试使用超过14 MB的输入时，都会收到“内存不足”错误。

合并时，该进程的内存使用量将跃升至550MB以上。对于14MB的输入来说，这似乎过多。

我正在使用PDFBox版本1.8.5在IBM Websphere Application Server上本地运行此应用程序

我将堆大小增加到1024MB，尽管这使我可以使用更多文件进行输入，但是我很快遇到了相同的问题。

在评论者的建议下，我更改了将文档对合并在一起，然后进一步合并以前合并的对的方法。这使我比以前更进一步。我仍然遇到内存不足错误，文件大小约为30 MB，但是它更可行。

File sourceLoc = new File(System.getProperty("java.io.tmpdir") + "source_files");
File scratch = new File(System.getProperty("java.io.tmpdir") + "scratch.txt");
PDFMergerUtility merger = new PDFMergerUtility();

merger.setDestinationFileName(System.getProperty("java.io.tmpdir") + "merged.pdf");
for(File file : sourceLoc.listFiles())
    merger.addSource(file);
merger.mergeDocumentsNonSeq(new org.apache.pdfbox.io.RandomAccessFile(scratch, "rw"));

这是生成的日志：

JVMDUMP039I Processing dump event "systhrow", detail "java/lang/OutOfMemoryError" at      2014/08/01 13:01:50 - please wait.
JVMDUMP032I JVM requested System dump using 'C:\Working\IntranetApps\I-Document\Services\core.20140801.130150.2408.0001.dmp' in response to an event
JVMDUMP010I System dump written to C:\Working\IntranetApps\I-Document\Services\core.20140801.130150.2408.0001.dmp
JVMDUMP032I JVM requested Heap dump using 'C:\Working\IntranetApps\I-Document\Services\heapdump.20140801.130150.2408.0002.phd' in response to an event
JVMDUMP010I Heap dump written to C:\Working\IntranetApps\I-Document\Services\heapdump.20140801.130150.2408.0002.phd
JVMDUMP032I JVM requested Java dump using 'C:\Working\IntranetApps\I-Document\Services\javacore.20140801.130150.2408.0003.txt' in response to an event
JVMDUMP010I Java dump written to C:\Working\IntranetApps\I-Document\Services\javacore.20140801.130150.2408.0003.txt
JVMDUMP032I JVM requested Snap dump using 'C:\Working\IntranetApps\I-Document\Services\Snap.20140801.130150.2408.0004.trc' in response to an event
JVMDUMP010I Snap dump written to C:\Working\IntranetApps\I-Document\Services\Snap.20140801.130150.2408.0004.trc
JVMDUMP013I Processed dump event "systhrow", detail "java/lang/OutOfMemoryError".
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at org.apache.pdfbox.io.RandomAccessBuffer.clone(RandomAccessBuffer.java:69)
    at org.apache.pdfbox.cos.COSStream.clone(COSStream.java:72)
    at org.apache.pdfbox.cos.COSStream.<init>(COSStream.java:96)
    at org.apache.pdfbox.pdfparser.NonSequentialPDFParser.parseCOSStream(NonSequentialPDFParser.java:1513)
    at org.apache.pdfbox.pdfparser.NonSequentialPDFParser.parseObjectDynamically(NonSequentialPDFParser.java:1266)
    at org.apache.pdfbox.pdfparser.NonSequentialPDFParser.parseObjectDynamically(NonSequentialPDFParser.java:1192)
    at org.apache.pdfbox.pdfparser.NonSequentialPDFParser.parseDictObjects(NonSequentialPDFParser.java:1166)
    at org.apache.pdfbox.pdfparser.NonSequentialPDFParser.initialParse(NonSequentialPDFParser.java:479)
    at org.apache.pdfbox.pdfparser.NonSequentialPDFParser.parse(NonSequentialPDFParser.java:740)
    at org.apache.pdfbox.pdmodel.PDDocument.loadNonSeq(PDDocument.java:1306)
    at org.apache.pdfbox.pdmodel.PDDocument.loadNonSeq(PDDocument.java:1289)
    at org.apache.pdfbox.util.PDFMergerUtility.mergeDocuments(PDFMergerUtility.java:232)
    at org.apache.pdfbox.util.PDFMergerUtility.mergeDocumentsNonSeq(PDFMergerUtility.java:201)
    at com.my.pkg.MyMergeClass.main(MyMergeClass.java:90)