带有jsp：useBean的Javabean它们如何工作？我不明白

问题描述

我在index.jsp和Servlet之间又做了一个jsp文件：

 <jsp:useBean id="binOp" class="beans.BinaryOperation" scope="session"/>
<jsp:setProperty name="binOp" property="*"/>.

这做到了“魔术”。

解决方法

我必须使用Java bean从jsp文件中获取2个数字和一个运算。提交数字后，将它们从该Java Bean带到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的数字来完成。所以，我有了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放在程序包servlet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();
    }
}

然后将bean BinaryOperation放入程序包bean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)));
}
}

在Apache日志中，我有if语句的下一个输出（请参阅servlet-System.out.println（binOp.getNr1（）+
binOp.getNr2（）+ binOp.getOp（））;）：nullnullnull

我的错误在哪里？

jsp

带有jsp：useBean的Javabean它们如何工作？我不明白

问题描述

解决方法

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