自定义架构到XMP元数据

我想将自定义元数据写入pdf文件，这些文件不受XMP标准模式的支持，因此我编写了自己的模式，其中包含我自己的属性 . 我可以使用PDFBox或iTextPDF库将这些额外的自定义元数据成功写入我的PDF文件 . 但是，如果不解析XMP xml，我无法在客户端读取自定义元数据 .

我想应该有一些我不知道将自定义架构恢复到java类的API .

如果我正在考虑正确的方向，请帮助我，或者我是否真的需要解析xml以便在客户端获取我的自定义数据？

这是我用PDFBox库编写的代码

自定义元数据文件 .

package com.ecomail.emx.core.xmp;

import java.io.IOException;

import org.apache.jempbox.xmp.XMPMetadata;

public class EMXMetadata extends XMPMetadata {

public EMXMetadata() throws IOException {
    super();
}

public EMXSchema addEMXSchema() {
    EMXSchema schema = new EMXSchema(this);
    return (EMXSchema) basicAddSchema(schema);
}

public EMXSchema getEMXSchema() throws IOException {
    return (EMXSchema) getSchemaByClass(EMXSchema.class);
}
}

自定义架构文件 .

package com.ecomail.emx.core.xmp;

import java.util.List;

import org.apache.jempbox.xmp.XMPMetadata;
import org.apache.jempbox.xmp.XMPSchema;
import org.w3c.dom.Element;

public class EMXSchema extends XMPSchema {
public static final String NAMESPACE = "http://www.test.com/emx/elements/1.1/";

public EMXSchema(XMPMetadata parent) {
    super(parent, "test", NAMESPACE);
}

public EMXSchema(Element element, String prefix) {
    super(element, prefix);
}

public String getMetaDataType() {
    return getTextProperty(prefix + ":metaDataType");
}

public void setMetaDataType(String metaDataType) {
    setTextProperty(prefix + ":metaDataType", metaDataType);
}

public void removeRecipient(String recipient) {
    removeBagValue(prefix + ":recipient", recipient);
}

public void addRecipient(String recipient) {
    addBagValue(prefix + ":recipient", recipient);
}

public List<String> getRecipients() {
    return getBagList(prefix + ":recipient");
}
}

XML客户端文件 .

package com.ecomail.emx.core.xmp;

import java.util.GregorianCalendar;

import org.apache.jempbox.xmp.XMPMetadata;
import org.apache.jempbox.xmp.XMPSchemaDublinCore;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDDocumentCatalog;
import org.apache.pdfbox.pdmodel.PDDocumentInformation;
import org.apache.pdfbox.pdmodel.common.PDMetadata;

public class XMPClient {

private XMPClient() {
}

public static void main(String[] args) throws Exception {
    PDDocument document = null;

    try {
        document = PDDocument.load("/home/silver/SVNRoot/ecomail/trunk/sample.pdf");
        PDDocumentCatalog catalog = document.getDocumentCatalog();
        PDDocumentInformation info = document.getDocumentInformation();

        EMXMetadata metadata = new EMXMetadata();

        XMPSchemaDublinCore dcSchema = metadata.addDublinCoreSchema();
        dcSchema.setTitle(info.getTitle());
        dcSchema.addContributor("Contributor");
        dcSchema.setCoverage("coverage");
        dcSchema.addCreator("PDFBox");
        dcSchema.addDate(new GregorianCalendar());
        dcSchema.setDescription("description");
        dcSchema.addLanguage("language");
        dcSchema.setCoverage("coverage");
        dcSchema.setFormat("format");

        EMXSchema emxSchema = metadata.addEMXSchema();
        emxSchema.addRecipient("Recipient 1");
        emxSchema.addRecipient("Recipient 2");

        PDMetadata metadataStream = new PDMetadata(document);
        metadataStream.importXMPMetadata(metadata);
        catalog.setMetadata(metadataStream);

        document.save("/home/silver/SVNRoot/ecomail/trunk/sample1.pdf");
        document.close();

        document = PDDocument.load("/home/silver/SVNRoot/ecomail/trunk/sample1.pdf");

        PDDocumentCatalog catalog2 = document.getDocumentCatalog();
        PDMetadata metadataStream2 = catalog2.getMetadata();

        XMPMetadata metadata2 = metadataStream2.exportXMPMetadata();
        EMXSchema emxSchema2 = (EMXSchema) metadata2.getSchemaByClass(EMXSchema.class);
        System.out.println("recipients : " + emxSchema2.getRecipients());
    } finally {
        if (document != null) {
            document.close();
        }
    }
}
 }

在XMPClient文件中，我希望通过从类名中查询，从重新存在的元数据中获取EMXSchema对象 .

XMPMetadata metadata2 = metadataStream2.exportXMPMetadata();
EMXSchema emxSchema2 = (EMXSchema) metadata2.getSchemaByClass(EMXSchema.class);
System.out.println("recipients : " + emxSchema2.getRecipients());

但我得到Null指针异常表明找不到 . 任何人都可以帮助我，如果我正确的方式或我需要解析XMP以获得我的收件人 Value .

谢谢