encryptedslideshow.java

java 读写word excel ppt

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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
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       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
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   See the License for the specific language governing permissions and
   limitations under the License.
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package org.apache.poi.hslf;

import java.io.FileNotFoundException;

import org.apache.poi.hslf.exceptions.CorruptPowerPointFileException;
import org.apache.poi.hslf.record.CurrentUserAtom;
import org.apache.poi.hslf.record.DocumentEncryptionAtom;
import org.apache.poi.hslf.record.PersistPtrHolder;
import org.apache.poi.hslf.record.Record;
import org.apache.poi.hslf.record.UserEditAtom;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;
import org.apache.poi.poifs.filesystem.DocumentEntry;
import org.apache.poi.poifs.filesystem.DocumentInputStream;
import org.apache.poi.util.LittleEndian;

/**
 * This class provides helper functions for determining if a
 *  PowerPoint document is Encrypted. 
 * In future, it may also provide Encryption and Decryption
 *  functions, but first we'd need to figure out how 
 *  PowerPoint encryption is really done!
 *
 * @author Nick Burch
 */

public class EncryptedSlideShow
{
	/**
	 * Check to see if a HSLFSlideShow represents an encrypted
	 *  PowerPoint document, or not
	 * @param hss The HSLFSlideShow to check
	 * @return true if encrypted, otherwise false
	 */
	public static boolean checkIfEncrypted(HSLFSlideShow hss) {
		// Easy way to check - contains a stream
		//  "EncryptedSummary"
		POIFSFileSystem fs = hss.getPOIFSFileSystem();
		try {
			fs.getRoot().getEntry("EncryptedSummary");
			return true;
		} catch(FileNotFoundException fnfe) {
			// Doesn't have encrypted properties
		}
		
		// If they encrypted the document but not the properties,
		//  it's harder.
		// We need to see what the last record pointed to by the
		//  first PersistPrtHolder is - if it's a 
		//  DocumentEncryptionAtom, then the file's Encrypted
		DocumentEncryptionAtom dea = fetchDocumentEncryptionAtom(hss);
		if(dea != null) {
			return true;
		}
		return false;
	}
	
	/**
	 * Return the DocumentEncryptionAtom for a HSLFSlideShow, or
	 *  null if there isn't one.
	 * @return a DocumentEncryptionAtom, or null if there isn't one
	 */
	public static DocumentEncryptionAtom fetchDocumentEncryptionAtom(HSLFSlideShow hss) {
		// Will be the last Record pointed to by the 
		//  first PersistPrtHolder, if there is one
		
		CurrentUserAtom cua = hss.getCurrentUserAtom();
		if(cua.getCurrentEditOffset() != 0) {
			// Check it's not past the end of the file
			if(cua.getCurrentEditOffset() > hss.getUnderlyingBytes().length) {
				throw new CorruptPowerPointFileException("The CurrentUserAtom claims that the offset of last edit details are past the end of the file");
			}
			
			// Grab the details of the UserEditAtom there
			Record r = Record.buildRecordAtOffset(
					hss.getUnderlyingBytes(),
					(int)cua.getCurrentEditOffset()
			);
			if(! (r instanceof UserEditAtom)) { return null; }
			UserEditAtom uea = (UserEditAtom)r;
			
			// Now get the PersistPtrHolder
			Record r2 = Record.buildRecordAtOffset(
					hss.getUnderlyingBytes(),
					uea.getPersistPointersOffset()
			);
			if(! (r2 instanceof PersistPtrHolder)) { return null; }
			PersistPtrHolder pph = (PersistPtrHolder)r2;
			
			// Now get the last record
			int[] slideIds = pph.getKnownSlideIDs();
			int maxSlideId = -1;
			for(int i=0; i<slideIds.length; i++) {
				if(slideIds[i] > maxSlideId) { maxSlideId = slideIds[i]; }
			}
			if(maxSlideId == -1) { return null; }
			
			int offset = (
					(Integer)pph.getSlideLocationsLookup().get(
							new Integer(maxSlideId)
					) ).intValue();
			Record r3 = Record.buildRecordAtOffset(
					hss.getUnderlyingBytes(),
					offset
			);
			
			// If we have a DocumentEncryptionAtom, it'll be this one
			if(r3 instanceof DocumentEncryptionAtom) {
				return (DocumentEncryptionAtom)r3;
			}
		}
		
		return null;
	}
}