检查请求参数是否等于 Java 中的字符串
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Check if the request parameter equals a string in Java
提问by steve
I want to do this in java
我想在java中做到这一点
if(request.getParameter("page") == "page1")
// page1
else if(request.getParameter("page") == "page2")
// page2
For someone new to java, why doesn't the above code work, and what is the best way to do what I want to do above?
对于 Java 新手，为什么上面的代码不起作用，上面我想做的最好的方法是什么？
回答by BalusC
Since Stringis an object, not a primitive, the ==would only compare them by reference, not by the object's internal representation. You need to compare them by equals()instead.
由于String是一个对象，而不是一个原始对象，==因此只能通过引用来比较它们，而不是通过对象的内部表示。你需要比较它们equals()。
if("page1".equals(request.getParameter("page")))
// do something
else if("page2".equals(request.getParameter("page")))
// do something else
(note, this style is done so to prevent potential NullPointerExceptionon for example request.getParameter("page").equals("page1")when the parameter returns null)
（注意，这种风格是为了防止潜在NullPointerException的，例如request.getParameter("page").equals("page1")当参数返回时null）
Related questions:
相关问题：
Unrelated to the problem, the JSP is not the best place for this job. Consider a Servlet.
与问题无关，JSP 不是这项工作的最佳场所。考虑一个Servlet。
回答by jmort253
You are using the wrong equals. Try this:
您使用了错误的等号。试试这个：
if(request.getParameter("page") != null) {
if(request.getParameter("page").equals("page1")) {
// do stuff
} else if(request.getParameter("page").equals("page2")) {
// do other stuff
}
}
== compares the object references to see if they are equal, whereas .equals checks to see if the values of those object references are equal.
== 比较对象引用以查看它们是否相等，而 .equals 检查这些对象引用的值是否相等。
