在 servlet 中使用 POST 方法时接收空值？

Question

我想在 servlet 中使用 POST 方法发送一个字符串，以便它可以与其他域中的其他 servlet 应用程序通信。但我在 Input steam 对象中收到 null。

我的代码：

    String content = "10 141 nahush123 01";
    URL url = new URL("http://52.220.37.12:8080/servers/servers");
    System.out.println(url.toString());
    HttpURLConnection httpCon = (HttpURLConnection)url.openConnection();
    httpCon.setDoInput(true);
    httpCon.setDoOutput(true);
    httpCon.setRequestMethod("POST");
    httpCon.setRequestProperty("Content-Type", "text/plain;charset=UTF-8");

    OutputStream os = httpCon.getOutputStream();
    BufferedWriter out = new BufferedWriter(new OutputStreamWriter(os));
    out.write(content);
    //br = BufferReader(out);
    System.out.println(httpCon.getResponseCode());
    System.out.println(httpCon.getResponseMessage());
    writer.println(httpCon.getResponseMessage());


    httpCon.connect();
    br = new BufferedReader(new InputStreamReader(httpCon.getInputStream()));
    //reading response 
    //String resp;
    //if(br != null){
        content = br.readLine();
    //}
    System.out.println(content);
    writer.println(content);
    out.flush();
    writer.flush();
    writer.close();
    out.close();
    os.close();

Answer 1

使用您的传递字符串参数调用此方法：

public String postData(String reqStr) {
ObjectOutputStream objOS = null;
ObjectInputStream objIS = null;
HttpURLConnection servletCon = null;
try {
if (reqStr != null) {
Thread.sleep(1000);
objOS.writeObject(reqStr);
} else {
throw new Exception("request is null.");
}
} catch (Exception ex) {
        logger.error("Failed to send request to server.", ex);
    }
    String response = null;
    try {
        objIS = new ObjectInputStream(servletCon.getInputStream());
        response = (String) objIS.readObject();
    } catch (Exception ex) {
        logger.error("Failed to get response from server.", ex);
        response = null;
    }
    return response;
}

像你一样初始化连接，但调用方式不同：

public void initializeUrlConnection(String servletURL, String contentType, String method) {

    try {

        logger.debug("Servlet URL " + servletURL);
        url = new URL(servletURL);
        servletCon = (HttpURLConnection) url.openConnection();
        servletCon.setUseCaches(false);
        servletCon.setDefaultUseCaches(false);
        servletCon.setDoInput(true);
        servletCon.setDoOutput(true);
        servletCon.setRequestProperty("Content-Type", contentType);
        servletCon.setRequestMethod(method);
        objOS = new ObjectOutputStream(servletCon.getOutputStream());
    } catch (IOException ex) {

        logger.error("Failed to initialize Http Connection.", ex);
    }
}

调用初始化连接方法的第一个参数：

Object.initializeUrlConnection(url, contentType,method);

然后使用您的字符串/json 参数调用 posDataMethod：

Object.postData(str);

Answer 2

在我的 servlet 中复制粘贴代码运行良好

1. 检查您是否覆盖了 servlet 中的 doPost 方法

2. 检查您的帖子方法是否正常工作并返回值，我使用 "DHC Rest Client" chrome 插件。这是一个很酷的工具

3. 尝试删除 httpCon.connect() 行。没必要。

   来自关于 connect() 方法的 oracle 文档：

依赖于连接的操作，如 getContentLength，将 如有必要，隐式执行连接。

操作 getResponseMessage、getResponseCode 执行连接。

更新

我尝试使用我的本地测试 url 进行测试，它可以工作。然后我尝试了您的网址，但它不起作用。

您需要在使用输入流之前刷新输出流。

此代码有效并返回“0#5#26#Temperature#Living_Room#555555581#0+0#7#0#Room1#Master_bedroom#555555581#1+1#7#0#Door1#Living_Room#555555581#2 +1#6#0#frontdoor#Living_Room#555555581#2+0#6#0#doorback#Balcony#555555581#2+"

PrintWriter writer = res.getWriter();
String content = "10 141 nahush123 01";
URL url = new URL("http://52.220.37.12:8080/servers/servers");
System.out.println(url.toString());
HttpURLConnection httpCon = (HttpURLConnection)url.openConnection();
httpCon.setDoInput(true);
httpCon.setDoOutput(true);
httpCon.setRequestMethod("POST");
httpCon.setRequestProperty("Content-Type", "text/plain;charset=UTF-8");

OutputStream os = httpCon.getOutputStream();
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(os));
out.write(content);
out.flush();
//br = BufferReader(out);
System.out.println(httpCon.getResponseCode());
System.out.println(httpCon.getResponseMessage());
writer.println(httpCon.getResponseMessage());


//httpCon.connect();
BufferedReader br = new BufferedReader(new InputStreamReader(httpCon.getInputStream()));
//reading response
//String resp;
//if(br != null){
content = br.readLine();
//}
System.out.println(content);
writer.println(content);
writer.flush();
writer.close();
out.close();
os.close();

Answer 3

尝试在 servlet 中使用 getparameter() 函数