Java聊天项目在DBUtil类中添加删除好友的代码；

在DBUtil类中添加和删除好友的代码如下：

// 添加好友
public static void addFriend(String username, String friendName) {
    Connection conn = null;
    PreparedStatement pstmt = null;
    try {
        conn = getConnection();
        String sql = "INSERT INTO friends (username, friendname) VALUES (?, ?)";
        pstmt = conn.prepareStatement(sql);
        pstmt.setString(1, username);
        pstmt.setString(2, friendName);
        pstmt.executeUpdate();
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        close(conn, pstmt, null);
    }
}

// 删除好友
public static void deleteFriend(String username, String friendName) {
    Connection conn = null;
    PreparedStatement pstmt = null;
    try {
        conn = getConnection();
        String sql = "DELETE FROM friends WHERE username = ? AND friendname = ?";
        pstmt = conn.prepareStatement(sql);
        pstmt.setString(1, username);
        pstmt.setString(2, friendName);
        pstmt.executeUpdate();
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        close(conn, pstmt, null);
    }
}

其中，`addFriend`方法将好友关系插入到数据库中的`friends`表中，`deleteFriend`方法将好友关系从数据库中删除。这里假设`friends`表的结构为：

CREATE TABLE friends (
    id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(50) NOT NULL,
    friendname VARCHAR(50) NOT NULL
);