如何实现文章表publishedDate字段自动生成并写入数据库？

Hey there! Let's dig into why your publishedDate is ending up as NULL when you create a new article, and fix it for good.

First, let's break down the root issues with your current setup:

• The JSP's hidden field for publishedDate might not bind correctly to the Date type in your entity (since ${now} outputs a human-readable string that Spring can fail to parse into a valid Date object).
• The @Generated(GenerationTime.ALWAYS) annotation could conflict with your attempts to set the date, as it tells Hibernate to expect the database to generate this value—but your database column doesn’t have a default configured to do that.

Here are three reliable solutions, ordered by how robust and low-maintenance they are:

1. Use JPA's @PrePersist Annotation (Most Recommended) #

This method lets you set the date directly in the entity right before it’s saved to the database, so you don’t rely on front-end input or database configurations.

Update your Article entity class by adding a @PrePersist method:

@Entity
@Table
public class Article implements Serializable, Comparator<Article>{
    // ... your existing fields and methods

    @Column(name="publishedDate", columnDefinition = "TIMESTAMP")
    private Date publishedDate ;

    // Auto-set the date when the article is first saved
    @PrePersist
    protected void onCreate() {
        // Only set the date if it's null (avoids overwriting it during updates)
        if (publishedDate == null) {
            publishedDate = new Date();
        }
    }

    // ... your getters and setters
}

This method runs automatically when you save a new article, ensuring publishedDate is always populated with the current time. It leaves existing dates untouched when you update the article later.

2. Let the Database Auto-Generate the Date #

If you prefer to handle this at the database level, modify your entity’s publishedDate column to use a database default value:

@Entity
@Table
public class Article implements Serializable, Comparator<Article>{
    // ... your existing fields and methods

    // Remove the @Generated annotation, and add a DEFAULT rule to the column
    @Column(name="publishedDate", columnDefinition = "TIMESTAMP DEFAULT CURRENT_TIMESTAMP")
    private Date publishedDate ;

    // ... your getters and setters
}

This tells your database (like MySQL) to automatically insert the current timestamp whenever a new row is added and publishedDate isn’t provided explicitly.

3. Manually Set the Date in Your Controller #

If you want explicit control in your business logic, set the date in your save method before persisting the article:

@PostMapping("/admin/article/save")
public String saveArticle(@ModelAttribute Article article) {
    // Check if publishedDate is null (only applies to new articles)
    if (article.getPublishedDate() == null) {
        article.setPublishedDate(new Date());
    }
    // Save the article using your repository
    articleRepository.save(article);
    return "redirect:/admin/articles";
}

This bypasses any front-end date binding issues entirely.

Bonus: Fixing JSP Date Binding (If You Want to Keep Using It) #

If you still want to pass the date from the JSP, you need to format it correctly so Spring can parse it into a Date object:

1. Add the JSTL fmt taglib to your JSP:

<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>

2. Format the date into a parsable string:

<jsp:useBean id="now" class="java.util.Date" />
<fmt:formatDate value="${now}" pattern="yyyy-MM-dd HH:mm:ss" var="formattedNow" />
<form:hidden path="publishedDate" value="${formattedNow}" />

3. Add @DateTimeFormat to your entity’s field to tell Spring how to parse the string:

@DateTimeFormat(pattern = "yyyy-MM-dd HH:mm:ss")
@Column(name="publishedDate", columnDefinition = "TIMESTAMP")
private Date publishedDate ;

Note: This method is less reliable because front-end values can be tampered with or formatted incorrectly.

内容的提问来源于stack exchange，提问作者Quail UriBI