第一步，读取blob数据，

第二步，将blob数据转换成byte数组

第三步，将byte数据进行base64加密转换成字符串并回传

第四步，接收字符串

第五步，将img控件的src设置成"data:image/jpeg;base64,"+接收的字符串;

相关代码：

java：

public String getAccountImg(String alias)
{
String sql = "SELECT imgrawdata FROM wx_account WHERE alias = ?";
PreparedStatement ps = DBUtils.createPreparedStatement(DBUtils.connection, sql);
DBUtils.setString(ps, 1, alias);
ResultSet res = DBUtils.executeQuery(ps);
DBUtils.next(res);

Blob imagerawdata = http://www.mamicode.com/DBUtils.getBlob(res,"imgrawdata");
byte[] b = blobToBytes(imagerawdata);
return Base64.encode(b);
}
private byte[] blobToBytes(Blob blob) {

BufferedInputStream is = null;

try {
is = new BufferedInputStream(blob.getBinaryStream());
byte[] bytes = new byte[(int) blob.length()];
int len = bytes.length;
int offset = 0;
int read = 0;

while (offset < len && (read = is.read(bytes, offset, len - offset)) >= 0) {
offset += read;
}
return bytes;
} catch (Exception e) {
return null;
} finally {
try {
is.close();
is = null;
} catch (IOException e) {
return null;
}
}
}

~~~~~~~~~~~~~~

js：

var img= xmlhttp.responseText;
alert(img);
document.getElementById("image").src = "data:image/jpeg;base64,"+img;