如何解决带有jsp：useBean的Javabean它们如何工作？我不明白
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？
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