网上介绍了很多使用HttpURLConnection调用action上传附件的问题, 但是我试了很多遍问题还是得不到解决。

1. 我在服务端使用Servlet 3内置的Part来处理附件上传, 一开始直接在html页面调用, 一些没有问题, 并保存了输入流.

2. 然后我根据之前保存的输入流在HttpURLConnection中生成一样的String并发送到服务端, 发送的代码如下：

package com.alex.client.test;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

public class TestAccessor {

	private static final String BOUNDARY = "-----------------------------11538186919912";

	private static final String END = "\r\n";

	public static void main(String[] args) {

		String site = "http://localhost:8080/webTest/login";
		// String param = "internatID=caowj@cn.ibm.com&password=111";

		try {
			test(site, null);
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	static void test(String site, String param) throws IOException {

		URL url = new URL(site);
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();

		conn.setDoInput(true);
		conn.setDoOutput(true);
		conn.setRequestMethod("POST");
		conn.setRequestProperty("connection", "Keep-Alive");
		conn.setRequestProperty("Charsert", "UTF-8");
		conn.setRequestProperty("User-Agent",
				"Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");
		conn.setRequestProperty("Content-Type", "multipart/form-data; boundary="
				+ BOUNDARY);

		StringBuilder sb = new StringBuilder();

		Map<String, String> paramMap = new HashMap<String, String>();	
		paramMap.put("internatID", "caowj@cn.ibm.com");
		paramMap.put("password", "111");

		// append general parameters
		sb.append(generalParam(paramMap));

		// append file attachment
		sb.append(BOUNDARY).append(END);
		sb.append(
				"Content-Disposition: form-data; name=\"attachment\"; filename=\"focus_accounts.cmd\"")
				.append(END);
		sb.append("Content-Type: application/octet-stream").append(END);
		sb.append(END);

		BufferedReader reader = new BufferedReader(new FileReader(new File(
				"E:\\CMMouse\\focus_accounts.cmd")));

		String line = null;

		while ((line = reader.readLine()) != null) {
			sb.append(line + END);
		}

		reader.close();
		// extra file attachment, please do not remove
		sb.append(END);
		
		sb.append(BOUNDARY + "--");

		PrintWriter out = new PrintWriter(conn.getOutputStream());
		out.write(sb.toString());
		out.flush();
		out.close();

		// read return io stream
		BufferedReader rtReader = new BufferedReader(new InputStreamReader(
				conn.getInputStream()));

		
		System.out.println(conn.getResponseCode());
		String liner = null;

		while ((liner = rtReader.readLine()) != null) {
			System.out.println(liner);
		}

	}

	static StringBuilder generalParam(Map<String, String> generalParam) {

		StringBuilder sb = new StringBuilder();

		for (String key : generalParam.keySet()) {
			sb.append(BOUNDARY).append(END);
			sb.append("Content-Disposition: form-data; name=\"");
			sb.append(key);
			sb.append("\"");
			sb.append(END).append(END);
			sb.append(generalParam.get(key) + END);
		}
		return sb;
	}
}

但是调用的结果却始终是报错, 服务端的报错堆栈如下:

八月 12, 2013 3:18:01 下午 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [com.alex.test.LoginServlet] in context with path [/webTest] threw exception
java.lang.NullPointerException
	at com.alex.test.LoginServlet.doPost(LoginServlet.java:49)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)

客户端的异常信息如下:

java.io.IOException: Server returned HTTP response code: 500 for URL: http://localhost:8080/webTest/login
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
	at com.alex.client.test.TestAccessor.test(TestAccessor.java:86)
	at com.alex.client.test.TestAccessor.main(TestAccessor.java:26)

我在服务端打印出的输入流都是一模一样的, 对使用浏览器生成的IO流和代码产生的IO流进行MD5校验结果也是相同的, 我实在是找不出什么办法了, 求各位大神提点.