Write data in file

Question

I found this example how to read binary file from PostgreSQL.

conn.setAutoCommit(false);

        // Get the Large Object Manager to perform operations with
        LargeObjectManager lobj = ((org.postgresql.PGConnection) conn).getLargeObjectAPI();

        ps = conn.prepareStatement("SELECT FILE FROM KNOWLEDGEBASE_FILES WHERE ID = ?");
        ps.setInt(1, 333);
        ResultSet rs = ps.executeQuery();
        while (rs.next())
        {
            // Open the large object for reading
            long oid = rs.getLong(1);
            LargeObject obj = lobj.open(oid, LargeObjectManager.READ);

            // Read the data
            byte buf[] = new byte[obj.size()];
            obj.read(buf, 0, obj.size());
            // Do something with the data read here


            FileChannel rwChannel = new RandomAccessFile("License_Agreement.pdf", "rw").getChannel();
            ByteBuffer wrBuf = rwChannel.map(FileChannel.MapMode.READ_WRITE, 0, buffer.length * number_of_lines);
            for (int i = 0; i < obj.size(); i++)
            {
                wrBuf.put(obj);
            }

            // Close the object
            obj.close();
        }
        rs.close();
        ps.close();

        // Finally, commit the transaction.
        conn.commit();

How I can write the data into file using NIO?

At this line wrBuf.put(obj); I get error:

no suitable method found for put(LargeObject) method ByteBuffer.put(byte) is not applicable (argument mismatch; LargeObject cannot be converted to byte) method ByteBuffer.put(ByteBuffer) is not applicable (argument mismatch; LargeObject cannot be converted to ByteBuffer) method ByteBuffer.put(byte[]) is not applicable (argument mismatch; LargeObject cannot be converted to byte[])

Meiko Rachimow · Accepted Answer · 2016-04-04 21:28:22Z

1

You could use LargeObject::getInputStream:

import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;
//...
while (rs.next())
{
    long oid = rs.getLong(1);
    LargeObject obj = lobj.open(oid, LargeObjectManager.READ);
    Path targetPath = FileSystems.getDefault().getPath("License_Agreement.pdf");
    Files.copy(obj.getInputStream(), targetPath, StandardCopyOption.REPLACE_EXISTING);
    obj.close();
}

answered Apr 4, 2016 at 21:28

Meiko Rachimow

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5 Comments

Peter Penzov Over a year ago

For some reason the file is not created after I run the code.

Meiko Rachimow Over a year ago

the file is not writeable, has the user the necessary rights? did you get a stacktrace?

Peter Penzov Over a year ago

Yes, there are no write restrictions

Peter Penzov Over a year ago

I found the problem. How I can configure the Java code to write in JUnit resource directory - src\test\resources

Meiko Rachimow Over a year ago

this should do it: FileSystems.getDefault().getPath("src/test/resources", "License_Agreement.pdf"); (see: docs.oracle.com/javase/7/docs/api/java/nio/file/…)

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