Java 在 JSP 中定义类
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Defining a class in a JSP
提问by Vivin Paliath
Please don't punch me in the face! I know this flies in the face of good design, but I'm simply writing a test page to demonstrate something. Our webapp module (correctly) has no direct access to our domain classes. I don't want to create a whole class outside of the JSP, since the page is just for demonstration purposes, and I don't want to write a lot of extraneous code for the same reason. I was trying to define a class the usual way in the JSP, but that didn't work (threw a lot of compile-time errors). This is a quick-n-dirty, one-time deal (I'll be getting rid of it once I'm done). I'd just like to know if this is possible or not. If not, then I will go the long way.
请不要打我的脸！我知道这与好的设计背道而驰，但我只是在写一个测试页面来演示一些东西。我们的 webapp 模块（正确地）无法直接访问我们的域类。我不想在 JSP 之外创建一个完整的类，因为该页面仅用于演示目的，出于同样的原因，我不想编写很多无关的代码。我试图在 JSP 中以通常的方式定义一个类，但这不起作用（抛出了很多编译时错误）。这是一项快速而肮脏的一次性交易（完成后我将摆脱它）。我只想知道这是否可能。如果没有，那么我会走很长的路。
<%
public class Person {
private int id;
private int age;
private String name;
/*
... ctor and getters and setters
*/
}
%>
And the errors I got:
我得到的错误：
convert-jsp-to-java:
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
An error occurred at line: 57 in the generated java file
Syntax error on token "class", invalid VariableDeclarator
An error occurred at line: 73 in the generated java file
The return type is incompatible with Object.getClass()
An error occurred at line: 74 in the generated java file
Syntax error on token "class", Identifier expected
An error occurred at line: 77 in the generated java file
Syntax error on token "class", invalid VariableDeclaratorId
An error occurred at line: 78 in the generated java file
Syntax error on token "this", PrimitiveType expected
An error occurred at line: 78 in the generated java file
Syntax error on token "class", invalid Expression
An error occurred at line: 79 in the generated java file
Syntax error on token "class", invalid Expression
采纳答案by Hyman Leow
I don't see why it wouldn't be possible. A JSP is just another way of writing a Servlet, so you should be able to create classes as static (or for that matter, non-static) inner classes within the Servlet, as you would any other class, using the <%! %> convention.
我不明白为什么这不可能。JSP 只是编写 Servlet 的另一种方式，因此您应该能够在 Servlet 中将类创建为静态（或就此而言，非静态）内部类，就像创建任何其他类一样，使用 <%! %> 约定。
I was able to do a quick, functional, proof of concept:
我能够做一个快速的、功能性的、概念证明：
<%@page contentType="text/html" pageEncoding="MacRoman"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<%!
private static class NdBadIdea {
private final int foo = 42;
public int getFoo() {
return foo;
}
}
%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=MacRoman">
<title>JSP Page</title>
</head>
<body>
<h1>Hello World!</h1>
<%=new NdBadIdea().getFoo()%>
</body>
</html>
回答by axtavt
Just for information: code snippet from the question declares a nested class(i.e. a class, declared inside a method body). It would be legal without publickeyword:
仅供参考：问题中的代码片段声明了一个嵌套类（即在方法体内声明的类）。没有public关键字是合法的：
<%
class Person {
...
}
%>
