带 jsp 的 Javabean :useBean. 它们如何工作？我不明白-6ren

带 jsp 的 Javabean :useBean. 它们如何工作？我不明白

转载作者：行者123 更新时间：2023-12-01 05:53:10

我必须使用 java bean 从 jsp 文件中获取 2 个数字和一个操作。提交数字后，将它们从该 Java Bean 传送到 servlet 并返回它们的结果。问题是 java bean 字段永远不会用文本框中写入的数字来完成。所以，我有index.jsp的主体:

<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>JSP Page</title>
    <link rel="stylesheet" type="text/css" href="style.css" />
</head>
<body>
    <h1>Calculator</h1>
    <FORM METHOD="POST" action="Controller">
        N1: <input type ="text" name="nr1" value="0">
        op: <input type ="text" name="op" value="+">
        N2: <input type ="text" name="nr2" value="0">
        <INPUT class ="button" TYPE="submit" NAME="actiune" VALUE="Calculate"/>
    </FORM>
    <jsp:useBean id="binOp" class="beans.BinaryOperation" scope="session"/>
    <jsp:setProperty name="binOp" property="*"/>
</body>

servlet 的 processRequest 方法 Controller.java，放置在 servlet 包中:

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    HttpSession session = request.getSession(true);
    BinaryOperation binOp = (BinaryOperation) session.getAttribute("binOp");

    try {
        if (!binOp.isComplete()) {
            System.out.println(binOp.getNr1() + binOp.getNr2() + binOp.getOp());
            response.sendRedirect("index.jsp");
        } else {
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet Controller</title>");
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Bean in controller " + binOp.getNr1() + "__" + binOp.getOp() + "__" + binOp.getNr2() + "</h1>");
            out.println(binOp.toString());
            out.println("</body>");
            out.println("</html>");
        }



    } finally {
        out.close();
    }
}

并将 bean BinaryOperation 放置在包 beans 中:

package beans;


public class BinaryOperation {

private String nr1;
private String op;
private String nr2;

public void setNr1(String nr1) {
    this.nr1 = nr1;
}

public void setOp(String op) {
    this.op = op;
}

public void setNr2(String nr2) {
    this.nr2 = nr2;
}

public String getNr1() {
    return nr1;
}

public String getOp() {
    return op;
}

public String getNr2() {
    return nr2;
}

public boolean isComplete() {
    return !(((nr1 == null) || (nr1.length() == 0))
            || ((op == null) || (op.length() == 0))
            || ((nr2 == null) || (nr2.length() == 0)));
}
}