动态jsp页面转PDF输出到页面的实现方法

实现将动态jsp页面转成PDF输出到页面的方法可以通过Java的iText库来实现。主要思路是生成jsp页面的HTML文本，然后使用iText将HTML转换成PDF格式的文档，并将生成的PDF文档输出到页面上。

以下是实现该方法的详细步骤：

1. 引入iText库

在项目中引入iText库的jar包。iText提供了将HTML转换成PDF的功能，可通过以下代码引入iText：

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13.2</version>
</dependency>

2. 生成jsp页面的HTML文本

使用Java代码来生成jsp页面的HTML文本。具体可参考以下代码：

StringBuffer sb = new StringBuffer();
try {
    URL url = new URL("http://example.com/your-page.jsp");
    URLConnection conn = url.openConnection();
    BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
    String inputLine;
    while ((inputLine = br.readLine()) != null) {
        sb.append(inputLine);
    }
    br.close();
} catch (Exception ex) {
    ex.printStackTrace();
}
String htmlContent = sb.toString();

此代码将从指定的URL读取jsp页面的HTML代码并存储在htmlContent 变量中。

3. 将HTML转换成PDF

使用iText库中提供的XMLWorkerHelper类，将上一步中获得的HTML文本转换成PDF格式的文件。

此步骤的代码示例如下：

OutputStream file = new FileOutputStream(new File("example.pdf"));
Document document = new Document();
PdfWriter writer = PdfWriter.getInstance(document, file);
document.open();
InputStream is = new ByteArrayInputStream(htmlContent.getBytes());
XMLWorkerHelper.getInstance().parseXHtml(writer, document, is);
document.close();
file.close();

这段代码创建了一个Document对象，然后从HTML文本创建了一个InputStream对象。最后使用XMLWorkerHelper类将HTML转换成PDF，并将生成的PDF文件输出到指定的文件路径上。

4. 将PDF文件输出到页面

通过以下方法将生成的PDF文件输出到页面上：

response.setContentType("application/pdf");
response.setHeader("Content-Disposition", "inline; filename=" + fileName);
response.setContentLength((int)file.length());

ServletOutputStream out = response.getOutputStream();
byte[] bytes = new byte[1024];
int bytesRead = -1;
while ((bytesRead = fileInputStream.read(bytes)) != -1) {
    out.write(bytes, 0, bytesRead);
}
out.flush();
fileInputStream.close();

这段代码设置了response的content type和一些header信息。然后获取response的输出流，从生成的PDF文件中读取文件并将其写入到输出流中来输出到页面。

示例：

示例1：

以下是一个在jsp中生成PDF并输出到页面的完整示例。

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@page import="java.net.*,java.io.*"%>
<%@page import="com.itextpdf.text.*,com.itextpdf.text.pdf.*,com.itextpdf.text.Font.*,com.itextpdf.text.pdf.parser.*"%>

<%
    String pdfFileName = "example.pdf";
    String url = "http://example.com/your-page.jsp";

    // get the jsp page's HTML content as a string
    StringBuffer sb = new StringBuffer();
    try {
        URL urlObj = new URL(url);
        URLConnection conn = urlObj.openConnection();
        BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        String inputLine;
        while ((inputLine = br.readLine()) != null) {
            sb.append(inputLine);
        }
        br.close();
    } catch (Exception ex) { 
        ex.printStackTrace(); 
    }
    String htmlContent = sb.toString();

    // create a PDF writer object
    Document document = new Document();
    PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream(pdfFileName));
    document.open();

    // add the jsp page's HTML content as a paragraph to the PDF document object
    Paragraph paragraph = new Paragraph();
    paragraph.add(new Paragraph("\n"));
    HTMLWorker htmlWorker = new HTMLWorker(document);
    htmlWorker.parse(new StringReader(htmlContent));
    document.add(paragraph);

    // close the document
    document.close();
%>

<% 
    // output the PDF file to the client browser
    response.setContentType("application/pdf");
    response.setHeader("Content-disposition", "inline; filename=" + pdfFileName);

    ServletOutputStream out = response.getOutputStream();
    FileInputStream fileInputStream = new FileInputStream(pdfFileName);
    byte[] bytes = new byte[1024];
    int bytesRead = -1;
    while ((bytesRead = fileInputStream.read(bytes)) != -1) {
        out.write(bytes, 0, bytesRead);
    }
    out.flush();
    fileInputStream.close();
%>

示例2：

以下是一个用 Spring MVC 实现在jsp中生成PDF并输出到页面的完整示例。

在pom.xml文件引入iText库

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13.2</version>
</dependency>

编写Servlet控制器

在Spring MVC控制器中处理HTTP请求。

@Controller
public class PdfController {

    @RequestMapping(value="/pdf", method=RequestMethod.GET)
    public void pdf(HttpServletRequest request, HttpServletResponse response) throws Exception {

        String htmlContent = getHtmlContent(request);

        // create a PDF writer object
        Document document = new Document();
        PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream("example.pdf"));
        document.open();

        // add the jsp page's HTML content as a paragraph to the PDF document object
        Paragraph paragraph = new Paragraph();
        paragraph.add(new Paragraph("\n"));
        HTMLWorker htmlWorker = new HTMLWorker(document);
        htmlWorker.parse(new StringReader(htmlContent));
        document.add(paragraph);

        // close the document
        document.close();

        // output the PDF file to the client browser
        response.setContentType("application/pdf");
        response.setHeader("Content-disposition", "inline; filename=example.pdf");

        ServletOutputStream out = response.getOutputStream();
        FileInputStream fileInputStream = new FileInputStream("example.pdf");
        byte[] bytes = new byte[1024];
        int bytesRead = -1;
        while ((bytesRead = fileInputStream.read(bytes)) != -1) {
            out.write(bytes, 0, bytesRead);
        }
        out.flush();
        fileInputStream.close();
    }

    private String getHtmlContent(HttpServletRequest request) throws Exception {
        URL urlObj = new URL(request.getRequestURL().toString().replaceFirst("http", "https"));
        URLConnection conn = urlObj.openConnection();
        BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        String inputLine;
        StringBuilder sb = new StringBuilder();
        while ((inputLine = br.readLine()) != null) {
            sb.append(inputLine);
        }
        return sb.toString();
    }

}

在jsp页面中添加链接来转到生成PDF的控制器

<a href="${pageContext.request.contextPath}/pdf" target="_blank">Click Here</a> to generate PDF

总之，在jsp页面中生成PDF并输出到页面，需要引入iText库，将jsp页面的HTML文本转换成PDF格式，并输出到页面上。在实现过程中，需要注意文件保存的位置及输出流的流程问题。

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