除了马克的答案，您可能想知道在哪里拆分长字符串。为此，您可以使用PDFont 方法getStringWidth。
把所有东西放在一起你会得到这样的东西（根据 PDFBox 版本略有不同）：
PDFBox 1.8.x
PDDocument doc = null;
try
{
doc = new PDDocument();
PDPage page = new PDPage();
doc.addPage(page);
PDPageContentStream contentStream = new PDPageContentStream(doc, page);
PDFont pdfFont = PDType1Font.HELVETICA;
float fontSize = 25;
float leading = 1.5f * fontSize;
PDRectangle mediabox = page.findMediaBox();
float margin = 72;
float width = mediabox.getWidth() - 2*margin;
float startX = mediabox.getLowerLeftX() + margin;
float startY = mediabox.getUpperRightY() - margin;
String text = "I am trying to create a PDF file with a lot of text contents in the document. I am using PDFBox";
List<String> lines = new ArrayList<String>();
int lastSpace = -1;
while (text.length() > 0)
{
int spaceIndex = text.indexOf(' ', lastSpace + 1);
if (spaceIndex < 0)
spaceIndex = text.length();
String subString = text.substring(0, spaceIndex);
float size = fontSize * pdfFont.getStringWidth(subString) / 1000;
System.out.printf("'%s' - %f of %f\n", subString, size, width);
if (size > width)
{
if (lastSpace < 0)
lastSpace = spaceIndex;
subString = text.substring(0, lastSpace);
lines.add(subString);
text = text.substring(lastSpace).trim();
System.out.printf("'%s' is line\n", subString);
lastSpace = -1;
}
else if (spaceIndex == text.length())
{
lines.add(text);
System.out.printf("'%s' is line\n", text);
text = "";
}
else
{
lastSpace = spaceIndex;
}
}
contentStream.beginText();
contentStream.setFont(pdfFont, fontSize);
contentStream.moveTextPositionByAmount(startX, startY);
for (String line: lines)
{
contentStream.drawString(line);
contentStream.moveTextPositionByAmount(0, -leading);
}
contentStream.endText();
contentStream.close();
doc.save("break-long-string.pdf");
}
finally
{
if (doc != null)
{
doc.close();
}
}
（BreakLongString.java 测试 testBreakString 用于 PDFBox 1.8.x）
PDFBox 2.0.x
PDDocument doc = null;
try
{
doc = new PDDocument();
PDPage page = new PDPage();
doc.addPage(page);
PDPageContentStream contentStream = new PDPageContentStream(doc, page);
PDFont pdfFont = PDType1Font.HELVETICA;
float fontSize = 25;
float leading = 1.5f * fontSize;
PDRectangle mediabox = page.getMediaBox();
float margin = 72;
float width = mediabox.getWidth() - 2*margin;
float startX = mediabox.getLowerLeftX() + margin;
float startY = mediabox.getUpperRightY() - margin;
String text = "I am trying to create a PDF file with a lot of text contents in the document. I am using PDFBox";
List<String> lines = new ArrayList<String>();
int lastSpace = -1;
while (text.length() > 0)
{
int spaceIndex = text.indexOf(' ', lastSpace + 1);
if (spaceIndex < 0)
spaceIndex = text.length();
String subString = text.substring(0, spaceIndex);
float size = fontSize * pdfFont.getStringWidth(subString) / 1000;
System.out.printf("'%s' - %f of %f\n", subString, size, width);
if (size > width)
{
if (lastSpace < 0)
lastSpace = spaceIndex;
subString = text.substring(0, lastSpace);
lines.add(subString);
text = text.substring(lastSpace).trim();
System.out.printf("'%s' is line\n", subString);
lastSpace = -1;
}
else if (spaceIndex == text.length())
{
lines.add(text);
System.out.printf("'%s' is line\n", text);
text = "";
}
else
{
lastSpace = spaceIndex;
}
}
contentStream.beginText();
contentStream.setFont(pdfFont, fontSize);
contentStream.newLineAtOffset(startX, startY);
for (String line: lines)
{
contentStream.showText(line);
contentStream.newLineAtOffset(0, -leading);
}
contentStream.endText();
contentStream.close();
doc.save(new File(RESULT_FOLDER, "break-long-string.pdf"));
}
finally
{
if (doc != null)
{
doc.close();
}
}
（BreakLongString.java 测试 testBreakString 用于 PDFBox 2.0.x）
结果
这看起来符合预期。
当然还有很多改进要做，但这应该说明如何去做。
添加无条件换行
在 aleskv 的评论中问：
当字符串中有\n时，你能添加换行符吗？
通过首先将字符串拆分为 '\n' 字符，然后遍历拆分结果，可以轻松地将解决方案扩展为在换行符处无条件中断。
例如if 而不是上面的长字符串
String text = "I am trying to create a PDF file with a lot of text contents in the document. I am using PDFBox";
您想用嵌入的换行符处理这个更长的字符串
String textNL = "I am trying to create a PDF file with a lot of text contents in the document. I am using PDFBox.\nFurthermore, I have added some newline characters to the string at which lines also shall be broken.\nIt should work alright like this...";
你可以简单地替换
String text = "I am trying to create a PDF file with a lot of text contents in the document. I am using PDFBox";
List<String> lines = new ArrayList<String>();
int lastSpace = -1;
while (text.length() > 0)
{
[...]
}
在上述解决方案中
String textNL = "I am trying to create a PDF file with a lot of text contents in the document. I am using PDFBox.\nFurthermore, I have added some newline characters to the string at which lines also shall be broken.\nIt should work alright like this...";
List<String> lines = new ArrayList<String>();
for (String text : textNL.split("\n"))
{
int lastSpace = -1;
while (text.length() > 0)
{
[...]
}
}
（来自BreakLongString.java 测试testBreakStringNL）
结果：