URL连接获取InputStream为空问题排查及URL编码修复咨询

1. URL参数分隔符错误是核心问题 #

你在代码里构造URL时误用了HTML转义字符&来分隔参数，但Java的URL类会把&当作普通字符串处理，进而在解析时再次转义，导致最终URL变成了&——这会让服务器完全无法正确识别请求参数，自然返回异常。

正确的做法是直接用&作为URL参数的分隔符，修改后的URL代码：

URL UrlOpenRequest = new URL("http://example.com/docs/modules/content/applet_controller.php?action=editObject&objectType=resource&objectTable=res_version_business&objectId=206");

2. POST请求体的参数分隔符也犯了同样错误 #

在写入POST表单数据时，你同样用了&来分隔fileContent和fileExtension，这会导致服务器无法解析POST参数。同样替换成普通的&：

writer.write("fileContent=" + this.fileContentTosend + "&fileExtension=" + this.fileExtension);

3. 缺少必要的请求头设置 #

发送POST表单数据时，必须设置Content-Type请求头为application/x-www-form-urlencoded，否则服务器可能无法识别请求体格式。在打开连接后添加这行代码：

HttpOpenRequest.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

4. 不要依赖available()判断响应数据 #

HttpURLConnection.getInputStream().available()只能返回当前已读取到内存的字节数，不代表整个响应的总长度，用它来判断是否有数据完全不准确，直接读取输入流即可。

额外提示：参数编码问题 #

如果fileContentTosend或fileExtension包含特殊字符（比如空格、&、=等），一定要用URLEncoder.encode()进行编码，避免参数解析混乱：

String encodedFileContent = URLEncoder.encode(this.fileContentTosend, "UTF-8");
String encodedFileExtension = URLEncoder.encode(this.fileExtension, "UTF-8");
writer.write("fileContent=" + encodedFileContent + "&fileExtension=" + encodedFileExtension);

完整修复后的代码片段 #

public void sendHttpRequest(String theUrl, String postRequest) throws Exception {
    // 修复URL参数分隔符
    URL UrlOpenRequest = new URL("http://example.com/docs/modules/content/applet_controller.php?action=editObject&objectType=resource&objectTable=res_version_business&objectId=206");
    System.out.println("UrlOpenRequest: " + UrlOpenRequest.toString());
    
    HttpURLConnection HttpOpenRequest = (HttpURLConnection) UrlOpenRequest.openConnection();
    HttpOpenRequest.setRequestMethod("POST");
    HttpOpenRequest.setRequestProperty("Accept", "*/*");
    // 添加必要的Content-Type请求头
    HttpOpenRequest.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
    HttpOpenRequest.setDoInput(true);
    HttpOpenRequest.setDoOutput(true);
    
    if (!"none".equals(postRequest)) {
        // 修复POST参数分隔符 + 可选参数编码
        String encodedFileContent = URLEncoder.encode(this.fileContentTosend, "UTF-8");
        String encodedFileExtension = URLEncoder.encode(this.fileExtension, "UTF-8");
        OutputStreamWriter writer = new OutputStreamWriter(HttpOpenRequest.getOutputStream());
        writer.write("fileContent=" + encodedFileContent + "&fileExtension=" + encodedFileExtension);
        writer.flush();
        writer.close(); // 记得关闭流释放资源
    } else {
        OutputStreamWriter writer = new OutputStreamWriter(HttpOpenRequest.getOutputStream());
        writer.write("foo=bar");
        writer.flush();
        writer.close();
    }
    
    // 直接读取输入流解析XML
    this.parse_xml(HttpOpenRequest.getInputStream());
    HttpOpenRequest.disconnect();
}

内容的提问来源于stack exchange，提问作者Imane