java - 如何从java servlet获取参数值

Question

我试图获取传递给 Java Servlet 的参数值，但返回的字符串不正确。我将值存储在映射中并检查键是否存在。

Map params;
params = request.getParameterMap();

String id = params.get("id").toString();
String data = params.get("data").toString();

System.out.println("streaming" + data + " with id of " + id);

但是，如果我通过 http://localhost:8080/Serv/stream/data?data=hereisdata&id=you 调用此 servlet，我的输出将如下所示:

streaming[Ljava.lang.String;@5e2091d3 with id of [Ljava.lang.String;@36314ab8

我错过了什么？

编辑:由于建议的答案不起作用，我将整个类(class)包括在内，因为我可能会在类(class)中搞砸一些事情:

import java.util.*;
import javax.servlet.http.HttpServletRequest;
import Engine.Streamer;


public class AnalyzerController {

    private Map params;
    private String pathInfo;
    private HttpServletRequest request;

    public AnalyzerController(HttpServletRequest request)
    {
        this.params = request.getParameterMap();
        this.pathInfo = request.getPathInfo();
    }

    public void processRequest()
    {
        System.out.println("procing with " + pathInfo);

        switch(pathInfo){
        case "/stream/data":
            if(params.containsKey("id") && params.containsKey("data")) processStream();
            break;
        }
    }

    private void processStream()
    {
        System.out.println("we are told to stream");
        String data = request.getParameter("data");
        String id = request.getParameter("id");
        Streamer stream = new Streamer();   

        stream.streamInput(data, "Analyzer", id);           
    }
}

这一行具体抛出了 NPE:String data = request.getParameter("data");

Answer 1

如果您查看 Request#getParameterMap() 的文档，它返回 Map类型 Map<String, String[]> 。因此，需要从值 String[] 中取出第一个元素从 map 返回的数组。

String id = params.get("id")[0];

当然，您可以避免这一切，直接使用 Request#getParameter() 从请求对象中获取参数。方法。

String id = request.getParameter("id");

编辑:查看您的类代码，似乎实例变量 request未初始化。在构造函数中初始化它，如下所示:

public AnalyzerController(HttpServletRequest request)
{
    this.request = request; // Initialize your instance variable request which is used in the other methods.
    this.params = request.getParameterMap();
    this.pathInfo = request.getPathInfo();
}