How to convert Blob to String and String to Blob in java

Question

I'm trying to get string from BLOB datatype by using

Blob blob = rs.getBlob(cloumnName[i]);
byte[] bdata = blob.getBytes(1, (int) blob.length());
String s = new String(bdata);

It is working fine but when I'm going to convert String to Blob and trying to insert into database then nothing inserting into database. I've used below code for converting String to Blob:

String value = (s);
byte[] buff = value.getBytes();
Blob blob = new SerialBlob(buff);

Can anyone help me about to converting of Blob to String and String to Blob in Java?

Lundquist

Firstly, you need to make sure you use the right term: it's blob, not blog. You'll get a lot further with web searches when you use the right name. Secondly, blobs are for binary data, not text data. Ideally you shouldn't be using them for text data in the first place, and if you do you should specify an encoding (e.g. UTF-8) when converting the text data to binary data. – Stonefly

Answer 1

try this (a2 is BLOB col)

PreparedStatement ps1 = conn.prepareStatement("update t1 set a2=? where id=1");
Blob blob = conn.createBlob();
blob.setBytes(1, str.getBytes());
ps1.setBlob(1, blob);
ps1.executeUpdate();

it may work even without BLOB, driver will transform types automatically:

   ps1.setBytes(1, str.getBytes);
   ps1.setString(1, str);

Besides if you work with text CLOB seems to be a more natural col type

Hessite

Answer 2

Use this to convert String to Blob. Where connection is the connection to db object.

    String strContent = s;
    byte[] byteConent = strContent.getBytes();
    Blob blob = connection.createBlob();//Where connection is the connection to db object. 
    blob.setBytes(1, byteContent);

Eyrie

Answer 3

How are you setting blob to DB? You should do:

 //imagine u have a a prepared statement like:
 PreparedStatement ps = conn.prepareStatement("INSERT INTO table VALUES (?)");
 String blobString= "This is the string u want to convert to Blob";
oracle.sql.BLOB myBlob = oracle.sql.BLOB.createTemporary(conn, false,oracle.sql.BLOB.DURATION_SESSION);
 byte[] buff = blobString.getBytes();
 myBlob.putBytes(1,buff);
 ps.setBlob(1, myBlob);
 ps.executeUpdate();

Sledge

First of all, the OP never stipulated that he is using Oracle RDMS. If he isn't, this code won't compile. – Albertson

Answer 4

And here is my solution, that always works for me

StringBuffer buf = new StringBuffer();
String temp;
BufferedReader bufReader = new BufferedReader(new InputStreamReader(myBlob.getBinaryStream()));
    while ((temp=bufReader.readLine())!=null) {
        bufappend(temp);
    }

Footprint

Answer 5

Here is my solution:

Retrieve blob column from the database and pass it to the below method.

 public static String blobToString(BLOB blob) throws Exception {

        byte[] data = new byte[(int) blob.length()];
        BufferedInputStream instream = null;
        try {
        instream = new BufferedInputStream(blob.getBinaryStream());
        instream.read(data);
        } catch (Exception ex) {
        throw new Exception(ex.getMessage());
        } finally {
        instream.close();
        }
        
        int chunk = 65536;
        ByteArrayInputStream bis = new ByteArrayInputStream(data);
        GZIPInputStream gis = new GZIPInputStream(bis);

         int length = 0;
        byte[] buffer = new byte[chunk];
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        while ((length = gis.read(buffer, 0, chunk)) != -1) {
        bos.write(buffer, 0, length);
        }

        gis.close();
        bis.close();
        bos.close();
        
        String str = bos.toString();
        System.out.println(str);
        return str;

    }

Corps

Answer 6

To convert Blob to String in Java:

byte[] bytes = baos.toByteArray();//Convert into Byte array
String blobString = new String(bytes);//Convert Byte Array into String

Statement

you will get the error "The method toByteArray() is undefined for the type Blob" for the first line – Fantasm