如何为iText-PDF生成的PDF正确配置行间距？

我正在开发一款生成PDF的应用，目前使用iText-PDF库进行概念验证（POC）。配置行间距时遇到问题：手动生成的PDF中红色行与黑色行间距紧凑符合预期，但通过代码生成的PDF里两行间距过大。

当前生成代码如下：

@Test
void testDocumentWithCustomFont() throws FileNotFoundException {
    inDocument(CUSTOM_FONT_DESTINATION, document -> {
        try {
            FontProgram fontProgram = FontProgramFactory.createFont(CUSTOM_FONT);
            PdfFont customFont = PdfFontFactory.createFont(fontProgram, PdfEncodings.IDENTITY_H,
                    PdfFontFactory.EmbeddingStrategy.PREFER_EMBEDDED);

            Text title = new Text("THIS IS A TITLE").setFont(customFont);
            title.setFontSize(18);
            document.add(new Paragraph(title).setTextAlignment(TextAlignment.CENTER).setMarginBottom(12));

            Text chordLine = new Text("THIS IS A RED LINE").setFont(customFont);
            chordLine.setFontSize(12);
            chordLine.setFontColor(ColorConstants.RED);
            document.add(new Paragraph(chordLine).setMarginBottom(0));

            Text lyricLine = new Text("THIS IS A BLACK LINE THAT SHOULD BE NEAR TO THE RED").setFont(customFont);
            lyricLine.setFontSize(12);
            document.add(new Paragraph(lyricLine));
        } catch (IOException e) {
            LOGGER.error(e.getMessage(), e);
        }
    });
}

private void inDocument(String destination, Consumer<Document> documentConsumer) throws FileNotFoundException {
    try (Document document = new Document(new PdfDocument(new PdfWriter(destination)))){
        documentConsumer.accept(document);
    }
}

问题出在两个独立Paragraph之间的默认间距上，仅设置setMarginBottom(0)不足以消除段落间的额外间距，需要结合调整spacing属性：

1. 对红色行的Paragraph，同时设置setMarginBottom(0)和setSpacingAfter(0)，取消该段落后的所有额外间距
2. 对黑色行的Paragraph，设置setSpacingBefore(0)，取消该段落前的额外间距

修改后的完整代码：

@Test
void testDocumentWithCustomFont() throws FileNotFoundException {
    inDocument(CUSTOM_FONT_DESTINATION, document -> {
        try {
            FontProgram fontProgram = FontProgramFactory.createFont(CUSTOM_FONT);
            PdfFont customFont = PdfFontFactory.createFont(fontProgram, PdfEncodings.IDENTITY_H,
                    PdfFontFactory.EmbeddingStrategy.PREFER_EMBEDDED);

            Text title = new Text("THIS IS A TITLE").setFont(customFont);
            title.setFontSize(18);
            document.add(new Paragraph(title).setTextAlignment(TextAlignment.CENTER).setMarginBottom(12));

            Text chordLine = new Text("THIS IS A RED LINE").setFont(customFont);
            chordLine.setFontSize(12);
            chordLine.setFontColor(ColorConstants.RED);
            // 调整红色行段落的底部间距和后间距
            document.add(new Paragraph(chordLine).setMarginBottom(0).setSpacingAfter(0));

            Text lyricLine = new Text("THIS IS A BLACK LINE THAT SHOULD BE NEAR TO THE RED").setFont(customFont);
            lyricLine.setFontSize(12);
            // 调整黑色行段落的前间距
            document.add(new Paragraph(lyricLine).setSpacingBefore(0));
        } catch (IOException e) {
            LOGGER.error(e.getMessage(), e);
        }
    });
}

private void inDocument(String destination, Consumer<Document> documentConsumer) throws FileNotFoundException {
    try (Document document = new Document(new PdfDocument(new PdfWriter(destination)))){
        documentConsumer.accept(document);
    }
}

说明：iText中margin和spacing是独立的属性，spacing用于控制段落与其他元素之间的额外间距，仅清除margin无法完全消除段落间的默认空隙，两者结合才能实现两行紧凑排列的效果。

内容的提问来源于stack exchange，提问作者Alvaro Pedraza