Generate previews Leave feedback

Interface	Method	Description
`com.groupdocs.parser.options.ICreatePageStream`	`createPageStream(pageNumber)`	Returns a `java.io.OutputStream` for the page preview. Required.
`com.groupdocs.parser.options.IReleasePageStream`	`releasePageStream(pageNumber, stream)`	Called when the page preview is written. Optional.
`com.groupdocs.parser.options.IPreviewPageRender`	`previewPageRender(pageRenderInfo)`	Receives `PageRenderInfo` before a page is rendered. Optional.

PreviewOptions also has setPreviewFormat (PreviewFormats.Png, PreviewFormats.Jpeg, PreviewFormats.Bmp), setDpi, setWidth, setHeight and setPageNumbers.

Here are the steps to generate document page previews:

Prepare the PreviewOptions object;
Instantiate the Parser object;
Call the generatePreview(PreviewOptions) method.

The following example shows how to generate document page previews:

const fs = require('fs');
const path = require('path');
const java = require('java');
const groupdocs = require('@groupdocs/groupdocs.parser');

const FileOutputStream = java.import('java.io.FileOutputStream');
const outputDir = 'previews';
fs.mkdirSync(outputDir, { recursive: true });

// Create an instance of Parser class to generate document page previews
const parser = new groupdocs.Parser('SampleWithToc.pdf');
try {
  // Implement ICreatePageStream: return a Java output stream for each page
  const createPageStream = java.newProxy('com.groupdocs.parser.options.ICreatePageStream', {
    createPageStream: (pageNumber) =>
      new FileOutputStream(path.join(outputDir, `preview_${pageNumber}.png`)),
  });
  // Create preview options
  const previewOptions = new groupdocs.PreviewOptions(createPageStream);
  // Set PNG as an output image format
  previewOptions.setPreviewFormat(groupdocs.PreviewFormats.Png);
  // Set DPI for the output image
  previewOptions.setDpi(72);
  // Generate previews
  parser.generatePreview(previewOptions);
} finally {
  parser.close();
}
process.exit(0);

For the three-page SampleWithToc.pdf this creates preview_1.png, preview_2.png and preview_3.png (612 x 792 pixels at 72 DPI).

Close page streams

To control when the page stream is closed, pass an IReleasePageStream implementation as the second constructor argument:

// Implement IReleasePageStream: close the stream when the page preview is written
const releasePageStream = java.newProxy('com.groupdocs.parser.options.IReleasePageStream', {
  releasePageStream: (pageNumber, stream) => stream.close(),
});
// Create preview options with both callbacks
const previewOptions = new groupdocs.PreviewOptions(createPageStream, releasePageStream);

Generate spreadsheet previews

Note
Spreadsheets are rendered by tiles. See the example below.

Here are the steps to generate spreadsheet page previews:

Prepare the PreviewOptions object;
Set the IPreviewPageRender callback to obtain the PageRenderInfo (row and column of each tile);
Instantiate the Parser object;
Call the generatePreview(PreviewOptions) method.

The following example shows how to generate spreadsheet page previews:

const fs = require('fs');
const path = require('path');
const java = require('java');
const groupdocs = require('@groupdocs/groupdocs.parser');

const FileOutputStream = java.import('java.io.FileOutputStream');
const outputDir = 'previews';

// Get the output file path. If the render info is set, then tile name is {PageNumber}/{Row}x{Column}.png
function getOutputPath(renderInfo, pageNumber) {
  const fileName = renderInfo == null
    ? `preview_${pageNumber}.png`
    : path.join(`${renderInfo.getPageNumber()}`,
      `${renderInfo.getRow(pageNumber)}x${renderInfo.getColumn(pageNumber)}.png`);
  const filePath = path.join(outputDir, fileName);
  fs.mkdirSync(path.dirname(filePath), { recursive: true });
  return filePath;
}

// Create an instance of Parser class to generate spreadsheet page previews
const parser = new groupdocs.Parser('sample.xlsx');
try {
  let renderInfo = null;
  // Create preview options
  const previewOptions = new groupdocs.PreviewOptions(
    java.newProxy('com.groupdocs.parser.options.ICreatePageStream', {
      createPageStream: (pageNumber) => new FileOutputStream(getOutputPath(renderInfo, pageNumber)),
    }));
  // Set the callback to obtain the render info
  previewOptions.setPreviewPageRender(
    java.newProxy('com.groupdocs.parser.options.IPreviewPageRender', {
      previewPageRender: (pageRenderInfo) => { renderInfo = pageRenderInfo; },
    }));
  // Set PNG as an output image format
  previewOptions.setPreviewFormat(groupdocs.PreviewFormats.Png);
  // Set DPI for the output image
  previewOptions.setDpi(72);
  // Generate previews
  parser.generatePreview(previewOptions);
} finally {
  parser.close();
}
process.exit(0);

For sample.xlsx (two worksheets) this creates previews/1/0x0.png and previews/2/0x0.png.

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Close page streams

Generate spreadsheet previews

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