我正在以流的形式传递2个文档，并尝试将它们合并为单个pdf . 在循环的第一次迭代中，一切正常，但在第二次迭代期间奇迹般地抛出空指针异常 . 传递的两个流实际上是相同的，被用作两个独立的流 .
代码：
public synchronized void doMerge(InputStream[] streams,OutputStream out) throws Exception {
System.out.println("Starting To Merge Files...");
System.out.println("Total Number Of Files To Be Merged..." +
streams.length + "\n");
try {
int fileIndex = 0;
Document document = null;
PdfCopy writer = null;
PdfReader reader = null;
for (fileIndex = 0; fileIndex < streams.length; fileIndex++) {
System.out.println("Loop No : "+ (fileIndex+1));
reader = new PdfReader(streams[fileIndex]);
System.out.println("Reader "+ (fileIndex+1) +" created successfully");
if (fileIndex == 0) {
document = new Document();
System.out.println("Document created successfully");
writer = new PdfSmartCopy(document, out);
System.out.println("Reader created successfully");
document.open();
}
writer.addDocument(reader);
System.out.println("Document "+ (fileIndex+1)+" merged" );
reader.close();
System.out.println("Reader "+ (fileIndex+1)+" closed" );
}
document.close();
System.out.println("Document successfully closed");
System.out.println("File has been merged and written to-" + out);
}
catch (Exception e) {
System.out.println(in exception block");
System.out.println(e.toString());
}
}
这是我在输入中发送2个流时得到的输出：
Loop No : 1
Reader 1 created successfully
Document created successfully
Reader created successfully
Document 1 merged
Reader 1 closed
Loop No : 2
in exception block
java.lang.NullPointerException