Java 空指针异常jnlp.FileSaveService

我正在尝试使用jnlp.FileSaveService来保存在java web app的contoroller中生成的“saveAs”.txt文件。我在这里找到了一些例子 我不完全理解这是如何工作的，我在这一行得到null poniter异常：

fc = fss.saveFileDialog(null, null, new ByteArrayInputStream(txt.getBytes()), null);

我是否向方法saveFileDialog传递了错误信息，还是传递了其他信息？我将感谢任何帮助

static private FileOpenService fos = null;
static private FileSaveService fss = null;
static private FileContents fc = null;

private static synchronized void initialize() {
    try {
        fos = (FileOpenService)ServiceManager.lookup("javax.jnlp.FileOpenService");
        fss = (FileSaveService)ServiceManager.lookup("javax.jnlp.FileSaveService");
    } catch (UnavailableServiceException e) {
    }
}

public static void save(String txt) {
    initialize();
    try {
        // Show save dialog if no name is already given
        if (fc == null) {
            fc = fss.saveFileDialog(null, null, new ByteArrayInputStream(txt.getBytes()), null);
            // file saved, done
            return;
        }
        // use this only when filename is known
        if (fc != null) {
            writeToFile(txt, fc);
        }
    } catch (IOException ioe) {ioe.printStackTrace(System.out);
    }
}

public static void saveAs(String txt) {
    initialize();
    try {
        if (fc == null) {
            // If not already saved. Save-as is like save
            save(txt);
        } else {
            fc = fss.saveAsFileDialog(null, null, fc);
            save(txt);
        }
    } catch (IOException ioe) {
        ioe.printStackTrace(System.out);
    }
}

private static void writeToFile(String txt, FileContents fc) throws IOException {
    int sizeNeeded = txt.length() * 2;
    if (sizeNeeded > fc.getMaxLength()) {
        fc.setMaxLength(sizeNeeded);
    }
    BufferedWriter os = new BufferedWriter(new OutputStreamWriter(fc.getOutputStream(true)));
    os.write(txt);
    os.close();
}

@RequestMapping(value = "/exportPhonebook.html", method = RequestMethod.POST)
public String exportPhonebook(Model model) {

    List<User> listOfAllUsers = phoneBookSer.fetchAllUsers();
    String phonebook = "";

    for (User user : listOfAllUsers) {
        phonebook = phonebook + user.getSurname() + " " + user.getName() + 
        ", Phone Number: " + user.getPhoneNumber() + ";\r\n" ;
    }

    saveAs(phonebook);
}

---

我采取了不同的方法来解决我的问题。我使用

content-disposition

保存控制器中生成的.txt文件。你可以在下面看到我的代码

private void setResponseHeaderTXT(HttpServletResponse response) {
    response.setContentType("text/plain; charset=UTF-8");
    response.setHeader("content-disposition", "attachment; filename=imenik.txt" );
} 
@RequestMapping(value = "/exportPhonebook.html", method = RequestMethod.POST)
public void exportPhonebook(Model model, HttpServletResponse response) {

    List<User> listOfAllUsers = phoneBookSer.fetchAllUsers();
    String phonebook = "";

    for (User user : listOfAllUsers) {
        phonebook = phonebook + user.getSurname() + " " + user.getName() + ", + 
        ", Phone number: " + user.getPhoneNumber() + ";\r\n" ;
    }

    try {
        setResponseHeaderTXT(response);
        OutputStream outputStream = response.getOutputStream();
        outputStream.write(phonebook.getBytes(Charset.forName("UTF-8")));
        outputStream.flush();
        outputStream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }   
}

private void setresponseheaderText（HttpServletResponse）{
response.setContentType（“text/plain；charset=UTF-8”）；
setHeader（“内容处置”、“附件；文件名=imenik.txt”）；
} 
@RequestMapping（value=“/exportPhonebook.html”，method=RequestMethod.POST）
public void exportPhonebook（模型，HttpServletResponse）{
List listOfAllUsers=phoneBookSer.fetchAllUsers（）；
字符串phonebook=“”；
for（用户：所有用户列表）{
phonebook=phonebook+user.getName（）+“”+user.getName（）+“”，+
，电话号码：“+user.getPhoneNumber（）+”；\r\n”；
}
试一试{
SetResponseHeaderText（响应）；
OutputStream OutputStream=response.getOutputStream（）；
outputStream.write（phonebook.getBytes（Charset.forName（“UTF-8”）））；
outputStream.flush（）；
outputStream.close（）；
}捕获（IOE异常）{
e、 printStackTrace（）；
}   
}

我用IText将电话簿导出为pdf格式时也做了类似的事情

private void setResponseHeaderPDF(HttpServletResponse response) {
    response.setContentType("application/pdf");
    response.setHeader("content-disposition", "attachment; filename=imenik.pdf" );
} 

@RequestMapping(value = "/exportPhonebook.html", method = RequestMethod.POST)
public void exportPhonebook(Model model, @RequestParam("buttonSpremiImenik") String buttonSpremiImenik, HttpServletResponse response, HttpServletRequest request) {

    try {
        setResponseHeaderPDF(response);
        Document document = new Document();
        ByteArrayOutputStream baosPDF = new ByteArrayOutputStream();
        PdfWriter pdfWriter = null;
        pdfWriter = PdfWriter.getInstance(document, baosPDF);
        document.open();
        addMetaData(document);
        addTitlePage(document);
        addContent(document);
        document.close();
        pdfWriter.close();
        OutputStream os = response.getOutputStream();
        baosPDF.writeTo(os);
        os.flush();
        os.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

private static Font catFont = new Font(Font.FontFamily.TIMES_ROMAN, 18,Font.BOLD);
private static Font smallBold = new Font(Font.FontFamily.TIMES_ROMAN, 12,Font.BOLD);
private static Font tableHeaderFont = new Font(Font.FontFamily.TIMES_ROMAN, 10,Font.BOLD);
public static String[][] FONTS = {{"c:/windows/fonts/arial.ttf", BaseFont.IDENTITY_H}};


private static void addMetaData(Document document) {
    document.addTitle("Phonebook");
    document.addSubject("phonebook");
    document.addKeywords("phonebook");
    document.addAuthor("John Smith");
    document.addCreator("John Smith");
}
private static void addTitlePage(Document document) throws DocumentException {
    Paragraph preface = new Paragraph();
    addEmptyLine(preface, 1);
    preface.add(new Paragraph("Phonebook", catFont));
    addEmptyLine(preface, 1);
    preface.add(new Paragraph("Generated: " + new Date(), smallBold));
    addEmptyLine(preface, 1);
    document.add(preface);
}

private void addContent(Document document) throws DocumentException {

    Paragraph paragraph = new Paragraph();
    addEmptyLine(paragraph, 1);

    // Add a table
    createTable(paragraph);

    // Now add all this to the document
    document.add(paragraph);
}


private static void addEmptyLine(Paragraph paragraph, int number) {
    for (int i = 0; i < number; i++) {
        paragraph.add(new Paragraph(" "));
    }
}
private void createTable(Paragraph paragraf) throws DocumentException {

    PdfPTable table = new PdfPTable(9);
    table.setTotalWidth(new float[]{ 58, 50, 95, 60, 60, 135, 60, 42, 30 });
    table.setLockedWidth(true);

    List<User> listOfAllUsers = phoneBookSer.fetchAllUsers();

    PdfPCell c1 = new PdfPCell(new Phrase("Prezime", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Ime", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Organizacijska jedinica", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Telefon", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Telefaks", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("E-mail", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Lokacija", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Kat", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Soba", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    table.setHeaderRows(1);


    BaseFont bf = null;
    try {
        bf = BaseFont.createFont(FONTS[0][0], FONTS[0][1], BaseFont.EMBEDDED);
    } catch (IOException e) {
        e.printStackTrace();
    }
    Font fontArial = new Font(bf, 9);

    //Automatically detects fonts
    //FontFactory.registerDirectories();
    //Font fontArial9 = FontFactory.getFont("Arial", 9);

    for (User user : listOfAllUsers) {
        PdfPCell cell1 = new PdfPCell(new Phrase(user.getPrezime(), fontArial));
        table.addCell(cell1);
        PdfPCell cell2 = new PdfPCell(new Phrase(user.getIme(), fontArial));
        table.addCell(cell2);
        PdfPCell cell3 = new PdfPCell(new Phrase(user.getOrganizacijskaJedinica(), fontArial));
        table.addCell(cell3);
        PdfPCell cell4 = new PdfPCell(new Phrase(user.getTelefon(), fontArial));
        table.addCell(cell4);
        PdfPCell cell5 = new PdfPCell(new Phrase(user.getTelefaks(), fontArial));
        table.addCell(cell5);
        PdfPCell cell6 = new PdfPCell(new Phrase(user.getEmail(), fontArial));
        table.addCell(cell6);
        PdfPCell cell7 = new PdfPCell(new Phrase(user.getLokacija(), fontArial));
        table.addCell(cell7);
        PdfPCell cell8 = new PdfPCell(new Phrase(user.getKat(), fontArial));
        table.addCell(cell8);
        PdfPCell cell9 = new PdfPCell(new Phrase(user.getBrojSobe(), fontArial));
        table.addCell(cell9);
    }

    paragraf.add(table);
}

private void setResponseHeaderPDF（HttpServletResponse）{
response.setContentType（“application/pdf”）；
setHeader（“内容处置”、“附件；文件名=imenik.pdf”）；
} 
@RequestMapping（value=“/exportPhonebook.html”，method=RequestMethod.POST）
public void exportPhonebook（模型，@RequestParam（“buttonspremimenik”）字符串buttonspremimenik，HttpServletResponse，HttpServletRequest）{
试一试{
setResponseHeaderPDF（响应）；
文档=新文档（）；
ByteArrayOutputStream=newbytearrayoutputstream（）；
PdfWriter PdfWriter=null；
pdfWriter=pdfWriter.getInstance（文档，pdf）；
document.open（）；
添加元数据（文件）；
添加标题页（文件）；
添加内容（文件）；
document.close（）；
pdfWriter.close（）；
OutputStream os=response.getOutputStream（）；
pdf.writeTo(os);；
os.flush（）；
os.close（）；
}捕获（例外e）{
e、 printStackTrace（）；
}
}
私有静态字体catFont=新字体（Font.FontFamily.TIMES_ROMAN，18，Font.BOLD）；
私有静态字体smallBold=新字体（Font.fontf家族.TIMES_-ROMAN，12，Font.BOLD）；
private static Font tableHeaderFont=新字体（Font.fontf家族.TIMES_-ROMAN，10，Font.BOLD）；
公共静态字符串[][]字体={{“c:/windows/FONTS/arial.ttf”，BaseFont.IDENTITY_H}；
私有静态void addMetaData（文档）{
文件。addTitle（“电话簿”）；
文件。添加主题（“电话簿”）；
document.addKeywords（“电话簿”）；
文件作者（以下简称“约翰·史密斯”）；
文件。addCreator（“约翰·史密斯”）；
}
私有静态void addTitlePage（文档文档）引发DocumentException{
段落前言=新段落（）；
addEmptyLine（前言，1）；
序言。添加（新段落（“电话簿”，catFont））；
addEmptyLine（前言，1）；
序言.添加（新段落（“生成：“+new Date（），smallBold））；
addEmptyLine（前言，1）；
文件.增加（序言）；
}
私有void addContent（文档）引发DocumentException{
段落=新段落（）；
addEmptyLine（第1款）；
//添加一个表
表（第段）；
//现在将所有这些添加到文档中
文件.添加（第段）；
}
专用静态void addEmptyLine（段落，整数）{
for（int i=0；iprivate void setResponseHeaderPDF(HttpServletResponse response) {
    response.setContentType("application/pdf");
    response.setHeader("content-disposition", "attachment; filename=imenik.pdf" );
} 

@RequestMapping(value = "/exportPhonebook.html", method = RequestMethod.POST)
public void exportPhonebook(Model model, @RequestParam("buttonSpremiImenik") String buttonSpremiImenik, HttpServletResponse response, HttpServletRequest request) {

    try {
        setResponseHeaderPDF(response);
        Document document = new Document();
        ByteArrayOutputStream baosPDF = new ByteArrayOutputStream();
        PdfWriter pdfWriter = null;
        pdfWriter = PdfWriter.getInstance(document, baosPDF);
        document.open();
        addMetaData(document);
        addTitlePage(document);
        addContent(document);
        document.close();
        pdfWriter.close();
        OutputStream os = response.getOutputStream();
        baosPDF.writeTo(os);
        os.flush();
        os.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

private static Font catFont = new Font(Font.FontFamily.TIMES_ROMAN, 18,Font.BOLD);
private static Font smallBold = new Font(Font.FontFamily.TIMES_ROMAN, 12,Font.BOLD);
private static Font tableHeaderFont = new Font(Font.FontFamily.TIMES_ROMAN, 10,Font.BOLD);
public static String[][] FONTS = {{"c:/windows/fonts/arial.ttf", BaseFont.IDENTITY_H}};


private static void addMetaData(Document document) {
    document.addTitle("Phonebook");
    document.addSubject("phonebook");
    document.addKeywords("phonebook");
    document.addAuthor("John Smith");
    document.addCreator("John Smith");
}
private static void addTitlePage(Document document) throws DocumentException {
    Paragraph preface = new Paragraph();
    addEmptyLine(preface, 1);
    preface.add(new Paragraph("Phonebook", catFont));
    addEmptyLine(preface, 1);
    preface.add(new Paragraph("Generated: " + new Date(), smallBold));
    addEmptyLine(preface, 1);
    document.add(preface);
}

private void addContent(Document document) throws DocumentException {

    Paragraph paragraph = new Paragraph();
    addEmptyLine(paragraph, 1);

    // Add a table
    createTable(paragraph);

    // Now add all this to the document
    document.add(paragraph);
}


private static void addEmptyLine(Paragraph paragraph, int number) {
    for (int i = 0; i < number; i++) {
        paragraph.add(new Paragraph(" "));
    }
}
private void createTable(Paragraph paragraf) throws DocumentException {

    PdfPTable table = new PdfPTable(9);
    table.setTotalWidth(new float[]{ 58, 50, 95, 60, 60, 135, 60, 42, 30 });
    table.setLockedWidth(true);

    List<User> listOfAllUsers = phoneBookSer.fetchAllUsers();

    PdfPCell c1 = new PdfPCell(new Phrase("Prezime", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Ime", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Organizacijska jedinica", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Telefon", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Telefaks", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("E-mail", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Lokacija", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Kat", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    c1 = new PdfPCell(new Phrase("Soba", tableHeaderFont));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    table.addCell(c1);

    table.setHeaderRows(1);


    BaseFont bf = null;
    try {
        bf = BaseFont.createFont(FONTS[0][0], FONTS[0][1], BaseFont.EMBEDDED);
    } catch (IOException e) {
        e.printStackTrace();
    }
    Font fontArial = new Font(bf, 9);

    //Automatically detects fonts
    //FontFactory.registerDirectories();
    //Font fontArial9 = FontFactory.getFont("Arial", 9);

    for (User user : listOfAllUsers) {
        PdfPCell cell1 = new PdfPCell(new Phrase(user.getPrezime(), fontArial));
        table.addCell(cell1);
        PdfPCell cell2 = new PdfPCell(new Phrase(user.getIme(), fontArial));
        table.addCell(cell2);
        PdfPCell cell3 = new PdfPCell(new Phrase(user.getOrganizacijskaJedinica(), fontArial));
        table.addCell(cell3);
        PdfPCell cell4 = new PdfPCell(new Phrase(user.getTelefon(), fontArial));
        table.addCell(cell4);
        PdfPCell cell5 = new PdfPCell(new Phrase(user.getTelefaks(), fontArial));
        table.addCell(cell5);
        PdfPCell cell6 = new PdfPCell(new Phrase(user.getEmail(), fontArial));
        table.addCell(cell6);
        PdfPCell cell7 = new PdfPCell(new Phrase(user.getLokacija(), fontArial));
        table.addCell(cell7);
        PdfPCell cell8 = new PdfPCell(new Phrase(user.getKat(), fontArial));
        table.addCell(cell8);
        PdfPCell cell9 = new PdfPCell(new Phrase(user.getBrojSobe(), fontArial));
        table.addCell(cell9);
    }

    paragraf.add(table);
}