Empty file after download

问题

I tried to implement file store in PostgreSQL using OID:

public void upload() throws SQLException, GSSException
{
    if (file != null)
    {
        try
        {
            InputStream inputStream = file.getInputStream();
            Connection conn = ds.getConnection();
            PreparedStatement ps = null;
            boolean committed = false;
            try
            {
                conn.setAutoCommit(false);

                ps = conn.prepareStatement("INSERT INTO PROCEDURE_FILES (ID, PROCEDURE_ID, FILE_NAME, FILE) "
                    + " VALUES (?, ?, ?, ?)");
                ps.setInt(1, obj.number);
                ps.setInt(2, obj.number);
                ps.setString(3, file.getSubmittedFileName());

                ps.setBlob(4, inputStream, inputStream.available());

                ps.executeUpdate();
                ps.close();

                conn.commit();
                committed = true;
            }
            catch (SQLException e)
            {
                e.printStackTrace();
            }

            finally
            {
                if (!committed)
                {
                    conn.rollback();
                }

                if (ps != null)
                {
                    ps.close();
                }
                conn.close();
            }
        }
        catch (IOException e)
        {
            FacesContext.getCurrentInstance().addMessage(null, new FacesMessage("Upload failed!"));
        }
    }
}

public void initFileDBData() throws SQLException, IOException
    {
        Connection conn = ds.getConnection();
        PreparedStatement ps = null;

        try
        {
            conn.setAutoCommit(false);

            ps = conn.prepareStatement("SELECT * FROM PROCEDURE_FILES WHERE ID = ?");

            ps.setInt(1, id);
            ResultSet rs = ps.executeQuery();
            while (rs.next())
            {
                String file_name = rs.getString("FILE_NAME");
                Blob oid = rs.getBlob("FILE");
                InputStream binaryStreasm = oid.getBinaryStream();

                FacesContext fc = FacesContext.getCurrentInstance();
                ExternalContext ec = fc.getExternalContext();

                ec.responseReset();
                ec.setResponseContentLength(binaryStreasm.available());
                ec.setResponseHeader("Content-Disposition", "attachment; filename=\"" + file_name + "\"");

                byte[] buf;

                buf = new byte[binaryStreasm.available()];
                int offset = 0;
                int numRead = 0;
                while ((offset < buf.length) && ((numRead = binaryStreasm.read(buf, offset, buf.length - offset)) >= 0))
                {
                    offset += numRead;
                }

                HttpServletResponse response
                    = (HttpServletResponse) FacesContext.getCurrentInstance()
                    .getExternalContext().getResponse();

                response.setContentType("application/octet-stream");
                response.setHeader("Content-Disposition", "attachment;filename=" + file_name);
                response.getOutputStream().write(buf);
                response.getOutputStream().flush();
                response.getOutputStream().close();
                FacesContext.getCurrentInstance().responseComplete();
            }
        }
        finally
        {
            if (ps != null)
            {
                ps.close();
            }
            conn.close();
        }
    } 

But when I try to download the file I always get file with size 0 bytes. How I can fix this problem?

I suppose that I'm not downloading the the file in a proper way?

回答1:

Peter, this worked for me with PostgreSQL 9.3 and Java OpenJDK 7.

Writing with LargeObjectAPI:

public static void main(String[] args) throws SQLException, FileNotFoundException, IOException {
    Connection conn = DriverManager.getConnection("jdbc:postgresql://localhost:5432/test01", "postgres", "postgres");
    conn.setAutoCommit(false);
    File file = new File("/home/user/Pictures/somePicture.jpg");
    FileInputStream fis = new FileInputStream(file);
    LargeObjectManager lom = PGConnection.class.cast(conn).getLargeObjectAPI();
    long oid = lom.createLO(LargeObjectManager.READ | LargeObjectManager.WRITE);
    LargeObject lob = lom.open(oid, LargeObjectManager.WRITE);
    byte[] buffer = new byte[2048];
    int s = 0;
    while ((s = fis.read(buffer, 0, buffer.length)) > 0) {
        lob.write(buffer, 0, s);
    }
    lob.close();
    fis.close();

    PreparedStatement ps = conn.prepareStatement("insert into test(id, name, content) values (nextval('test_id_seq'), ?, ?)");
    ps.setString(1, "foto01");
    ps.setLong(2, oid);
    ps.executeUpdate();
    ps.close();
    conn.commit();
}

Reading large object from database:

public static void main(String[] args) throws SQLException, FileNotFoundException, IOException {
        Connection conn = DriverManager.getConnection("jdbc:postgresql://localhost:5432/test01", "postgres", "postgres");
        conn.setAutoCommit(false);

        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery("select id, name, content from test");

        LargeObjectManager lom = PGConnection.class.cast(conn).getLargeObjectAPI();
        byte[] buffer = new byte[2048];
        int s = 0;
        while(rs.next()) {
            File file = new File("/tmp", rs.getLong("id") + "_" + rs.getString("name"));
            FileOutputStream fos = new FileOutputStream(file);
            LargeObject lob = lom.open(rs.getLong("content"), LargeObjectManager.READ);
            while((s = lob.read(buffer, 0, buffer.length)) > 0) {
                fos.write(buffer, 0, buffer.length);
            }
            lob.close();
            fos.close();
        }

        conn.close();
    }

Test table was defined as

create table test (id serial, name varchar(256), content oid);

来源：https://stackoverflow.com/questions/37092628/empty-file-after-download