When reading the XML file, the message "content is not allowed in Prolog" is returned.

After the XML file is edited using some editors, the error "content is not allowed in Prolog" is returned when you use dom4j to read the file.

The BOM is described as follows.

There is a character named "Zero Width no-break space" in the UCS encoding, and its encoding is feff. Fffe does not exist in the UCs, so it should not appear in actual transmission. We recommend that you transmit the character "Zero Width no-break space" before transmitting the byte stream in the UCS specification ". In this way, if the receiver receives feff, it indicates that the byte stream is big-Endian; if it receives fffe, it indicates that the byte stream is little-Endian. Therefore, the character "Zero Width no-break space" is also called Bom.

The UTF-8 does not need BOM to indicate the byte order, but BOM can be used to indicate the encoding method. The UTF-8 code for the character "Zero Width no-break space" is ef bb bf. So if the receiver receives a byte stream starting with ef bb bf, it will know that this is UTF-8 encoding.

Windows uses BOM to mark the encoding of text files.

The solution is to delete the BOM header.

See

Http://blog.csdn.net/oscar999/article/category/801452