Java 我不知道'；我不知道如何使用JPQL[AND]和[OR]

我做了一个可以搜索姓名和作者的书的应用程序。我使用JPQL来实现它。当我填写两个文本框（姓名和作者）时，它搜索正确。但我填写了一个文本框，它搜索不到。 如何修复

Book.java

@Table(name = "books")
@NamedQueries({
        @NamedQuery(name = "searchNameAndAuthor", query = "SELECT b FROM Book AS b WHERE b.book_name =:book_name and b.author=:author"),
        @NamedQuery(name = "searchNameAndAuthorCount", query = "SELECT count(b) FROM Book AS b WHERE b.book_name =:book_name and b.author=:author")
})
@Entity
public class Book {
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "isbn_code", length = 17)
    private Integer isbn_code;

    @Column(name = "book_name", length = 30, nullable = false)
    private String book_name;

    @Column(name = "author", length = 20)
    private String author;

    @Column(name = "publisher", length = 20)
    private String publisher;

    @Column(name = "publish_date", length = 8)
    private Date publish_date;

    @Column(name = "stock", length = 4)
    private Integer stock;

search.jsp

<c:import url="/WEB-INF/views/layout/app.jsp">
    <c:param name="content">
        <c:if test="${flush != null}">
            <div id="flush_success">
                <c:out value="${flush}"></c:out>
            </div>
        </c:if>
        <h2>図書館ようこそ</h2>
        <form method="POST" action="<c:url value='/books/search/result' />">
            <label for="book_name">調べたいタイトル</label><br /> <input type="text"
                name="book_name" value="${book_name}" /> <br />
            <br />
            <label for="author">著者</label><br /> <input type="text"
                name="author" value="${author}" /> <br />
            <br />
            <button type="submit">検索</button>
        </form>
    </c:param>
</c:import>

図書館ようこそ
調べたいタイトル




著者




検索

您还需要处理空案例。检查参数是否为null的一种方法是作为或条件

SELECT b FROM Book AS b WHERE (:book_name IS NULL OR b.book_name =:book_name) 
                          and (:author IS NULL OR  b.author=:author)

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我可以从数据库中选择数据。我非常感激！