java web实现实现一个“个人日志”系统：第一阶段实现功能：用户可注册、登录，发表个人日志（每个用户可以看到其他用户发的日志），可以对所有个人日志进行评论，可退出系统；第二阶段实现功能：用户可以修改或删除自己发布的个人日志，可以删除自己日志下的评论，可以删除自己对其他用户日志的评论（相关细节可自行根据合理性设计）的代码

好的，这里给您提供一份大致的代码实现参考，仅供参考：

1. 用户注册功能

@RequestMapping(value = "/register", method = RequestMethod.POST)
public String register(User user, Model model) {
    if (userService.createUser(user)) {
        model.addAttribute("msg", "注册成功，请登录！");
        return "login";
    } else {
        model.addAttribute("msg", "注册失败，请重试！");
        return "register";
    }
}

2. 用户登录功能

@RequestMapping(value = "/login", method = RequestMethod.POST)
public String login(User user, HttpSession session, Model model) {
    User loginUser = userService.checkUser(user);
    if (loginUser != null) {
        session.setAttribute("user", loginUser);
        return "redirect:/home";
    } else {
        model.addAttribute("msg", "用户名或密码错误！");
        return "login";
    }
}

3. 发表个人日志功能

@RequestMapping(value = "/addBlog", method = RequestMethod.POST)
public String addBlog(Blog blog, HttpSession session) {
    User user = (User) session.getAttribute("user");
    blog.setUserId(user.getId());
    blogService.addBlog(blog);
    return "redirect:/home";
}

4. 查看个人日志和评论功能

@RequestMapping(value = "/viewBlog/{id}", method = RequestMethod.GET)
public String viewBlog(@PathVariable("id") Long id, Model model) {
    Blog blog = blogService.getBlogById(id);
    List<Comment> comments = commentService.getCommentsByBlogId(id);
    model.addAttribute("blog", blog);
    model.addAttribute("comments", comments);
    return "viewBlog";
}

5. 评论个人日志和删除评论功能

@RequestMapping(value = "/addComment", method = RequestMethod.POST)
public String addComment(Comment comment, HttpSession session) {
    User user = (User) session.getAttribute("user");
    comment.setUserId(user.getId());
    commentService.addComment(comment);
    return "redirect:/viewBlog/" + comment.getBlogId();
}

@RequestMapping(value = "/deleteComment/{id}", method = RequestMethod.GET)
public String deleteComment(@PathVariable("id") Long id) {
    Comment comment = commentService.getCommentById(id);
    commentService.deleteComment(id);
    return "redirect:/viewBlog/" + comment.getBlogId();
}

6. 删除和修改个人日志功能

@RequestMapping(value = "/deleteBlog/{id}", method = RequestMethod.GET)
public String deleteBlog(@PathVariable("id") Long id) {
    blogService.deleteBlog(id);
    commentService.deleteCommentsByBlogId(id);
    return "redirect:/home";
}

@RequestMapping(value = "/editBlog/{id}", method = RequestMethod.GET)
public String editBlog(@PathVariable("id") Long id, Model model) {
    Blog blog = blogService.getBlogById(id);
    model.addAttribute("blog", blog);
    return "editBlog";
}

@RequestMapping(value = "/updateBlog", method = RequestMethod.POST)
public String updateBlog(Blog blog) {
    blogService.updateBlog(blog);
    return "redirect:/home";
}

以上代码仅供参考，具体实现过程可能还需要考虑其他因素。