使用抽象方法设计通用API，但在传递给匿名类时必须使用final 变量。有更好的方法来实现这一点吗？

Question

我正在尝试创建一个在 iText 之上运行的通用 API。该API的功能之一是允许用户将PDF分割为单独的页面，并允许用户在分割后将文本列表添加到每个pdf页面上。例如，一个20页的pdf，运行此过程后，我将有20个1页pdf，第一个pdf上将有一个文本000001，最后一个pdf上将有000020 pdf。因此，为了实现这一目标，我使用抽象方法，允许开发人员根据给定当前页码的文本格式编写代码。

public abstract class GenericText {

    /**
     * The X position of the text. (0, 0) is at the bottom left
     */
    private float x;

    /**
     * The Y position of the text. (0, 0) is at the bottom left
     */
    private float y;

    /**
     * The rotation of the text. Rotation 0, 90, 180, 270
     */
    private float rotation;

    /**
     * <code>com.itextpdf.text.pdf.BaseFont</code>. Determine the font for the text
     */
    private BaseFont font;

    /**
     * Determine the font size of the text
     */
    private float fontSize;

    /**
     * This tells whether text can only be placed first page or on every page
     */
    private ComponentPlacement placement;

    /**
     * Since the text that the user want to insert onto the Pdf might vary
     * from page to page, or from logical document to logical document, we allow
     * the user to write their own implementation of the text. To give the user enough
     * flexibility, we give them the reference to the physical page index, the logical page index. 
     * @param physcialPage The actual page number that the user current looking at
     * @param logicalPage A Pdf might contain multiples sub-documents, <code>logicalPage</code>
     * tell the user which logical sub-document the system currently looking at
     */
    public abstract String generateText(int physicalPage, int logicalPage);
    ...
}

PdfPrcessor.java：这是分割发生的地方

/**
 * This is the main process that will split the pdf into individual page, and text to each page
 */
public void splitPdf(String inputPdf, boolean isSplit, List<GenericText> textList, 
             String outputDir, String baseOutputName, String outputPdfName) throws IOException, DocumentException{
    ...
    PdfReader reader = new PdfReader(inputPdf)
    PdfContentByte cb = ... ;
    for(int physicalPageIndex=1 ; physicalPageIndex<=reader.getNumberOfPages(); physicalPageIndex ++)
       ...
       //Code to split PDF. Write each page to a separate pdf. For each pdf, insert all text inside `textList` onto the pdf
       ...
       //Insert text
       if(textList != null){
         for(GenericText textComponent : textList){
            String text = textComponent.generateText(physicalPageIndex, logicalPageIndex);
            addText(text, cb, textComponent.getFont(), textComponent.getFontSize(), textComponent.getX(), textComponent.getY(), textComponent.getRotation());
         }
       }
    }
    ...
}

所以在我的主类中我会这样做，

final String printName = printNameLookup.get(baseOutputName);
final String seq = config.getPrintJobSeq();
GenericText keyline = new GenericText(90, 640, 0, arial, 7, ComponentPlacement.FIRST_PAGE){
    @Override
    public String generateText(int physicalPage, int logicalPage) {
         return printName + seq + " " + Utils.right(String.valueOf(logicalPage), 6, '0');
    }
};
textList.add(keyline);
pdfProcess.splitPdf(inputPdfPath, true, textList, outputDir, baseOutputName, outputPdfName);

这工作很好，而且我认为它非常灵活，printName和seq已被声明为 final 以便在 generateText(intphysicalPage, int LogicalPage) 内传递。我如何设计它，以便它不需要 final 字段。 界面有帮助吗？我使用guava API，我可以做这个

ImmutableListMultimap<String, File> groups = Multimaps.index(pdfList,
new Function<File, String>(){
    public String apply(File input){
        String[] ids = getId(input.getName());
        PackageLog pl = logProcessor.lookUp(new Long(ids[0]), ids[1]);
        String printName = printNameLookup.get(getPackageName(pl, s));
    }   
});

logProcessor，并且printNameLookup不是final，我喜欢他们的方式设计，我现在正在阅读他们的资料，但这需要一些时间，任何具有设计知识的专家都可以给我一些启发吗？

Answer 1

将它们复制到最终变量中并使用它们。

String printName = printNameLookup.get(baseOutputName);
String seq = config.getPrintJobSeq();
// use these in the anonymous class.
final String finalPrintName = printName;
final String finalSeq = seq;

或使用数组

final String[] printName = { printNameLookup.get(baseOutputName) };
final String[] seq = { config.getPrintJobSeq() };

// use printName[0] and seq[0] everywhere.

Answer 2

您已经发现了模板方法设计模式。在这种情况下，将值复制到最终变量中就可以了。