The class libraries provided by java do not support all your existing functions. You must write your own classes.

It's an old problem. I never dared to do it before, but now I have to do it. What is it?

You need to add attachments when sending emails in java. However, I have no chance to add real files, only data streams, because the file data streams I get from the database are too late to be stored on the hard disk, however, javamail only supports sending FileSourceData. What should I do? As a result, I decomcompiled the code, modified the interface I needed, and then implemented BlobSourceData for sending blob files. The content is simple, but it is a huge step. It gives me a lot of confidence.

　　

/** BlobDataSource. java ** Created on 2008.7.9, am11: 48 ** To change this template, choose Tools | Template Manager * and open the template in the editor. */package mail; import java. io. inputStream; import java. io. outputStream; import java. io. file; import java. io. fileDescriptor; import java. io. fileNotFoundException; import java. io. fileInputStream; import java. io. fileOutputStream; import java. io. IOException; import java. SQL. SQLException; import javax. activation. *; import oracle. SQL. BLOB; import com. sun. activation. registries. mimeTypeFile; public class BlobDataSource implements DataSource {private BLOB _ blob = null; private FileTypeMap typeMap = null; private String _ fileName = null; public BlobDataSource (String fileName, BLOB blob) {_ fileName = fileName; _ blob = blob;}/*** This method will return an InputStream representing the * the data and will throw an IOException if it can not do so. this method will return a new * instance of InputStream with each invocation. ** @ return an InputStream */public InputStream getInputStream () throws IOException {try {return _ blob. getBinaryStream ();} catch (SQLException expection) {return null ;}} /*** This method will return an OutputStream representing the * the data and will throw an IOException if it can * not do so. this method will return a new instance of * OutputStream with each invocation. ** @ return an OutputStream */public OutputStream getOutputStream () throws IOException {try {return _ blob. getBinaryOutputStream ();} catch (SQLException expection) {return null ;}/ *** This method returns the MIME type of the data in the form of a * string. this method uses the currently installed FileTypeMap. if * there is no FileTypeMap explictly set, the FileDataSource will * callgetDefaultFileTypeMapMethod on * FileTypeMap to acquire a default FileTypeMap.Note: By * default, the FileTypeMap used will be a MimetypesFileTypeMap.** @ Return the MIME Type * @ see javax. activation. fileTypeMap # getDefaultFileTypeMap */public String getContentType () {return "application/octet-stream";}/*** ReturnNameOf this object. the FileDataSource * will return the file name of the object. ** @ return the name of the object. * @ see javax. activation. dataSource */public String getName () {return _ fileName;}/*** Return the File object that corresponds to this FileDataSource. * @ return the File object for the file represented by this object. */public File getFile () {return null;}/*** Set the FileTypeMap to use with this FileDataSource ** @ param map The FileTypeMap for this object. */public void setFileTypeMap (FileTypeMap map) {typeMap = map ;}}
 
 
Its call code is as follows:
    public boolean addFileAffix(String filename,BLOB blob) {                Logger.println("add file affix:" + filename);                try {                        BodyPart bp = new MimeBodyPart();                        BlobDataSource streamds = new BlobDataSource(filename,blob);                        bp.setDataHandler(new DataHandler(streamds));                        bp.setFileName(streamds.getName());                        mp.addBodyPart(bp);                        return true;                    } catch (Exception e) {                        System.err.println("add file affix:" + filename + " error ecured" + e);                        return false;                    }            }