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HTTP发送的数据有两种方式，一种是GET请求，一种是POST请求，GET请求就是简单的URL拼接参数，发送的参数长度也有限制。

而POST的参数可以设置在FORM中，参数长度也可以满足大多要求，有时从服务器的性能上考虑，防止恶意的GET尝试，很多接口都是限制POST方式的。

那么POST请求发送参数来说常用也有两种方式，一种是拼接参数和GET一样，但是发送方式指定为POST。

发送的数据不同，也可以在头上进行指定，这里的示例基于HttpClient。

这里也写个简单GET请求：

/**
 * Get请求
 */
public static String HttpGet(String url)  throws Exception{
    String jsonString = "";
    HttpClient client = new HttpClient(new HttpClientParams(), 
new SimpleHttpConnectionManager(true));
    client.getHttpConnectionManager().getParams().setConnectionTimeout
(15000); //通过网络与服务器建立连接的超时时间
    client.getHttpConnectionManager().getParams().setSoTimeout(60000); 
//Socket读数据的超时时间，即从服务器获取响应数据需要等待的时间
    GetMethod method = new GetMethod(url);
    method.setRequestHeader("Content-Type", "text/html;charset=UTF-8");
    try {
        client.executeMethod(method);
        jsonString = method.getResponseBodyAsString();
    } catch (Exception e) {
        jsonString = "error";
        logger.error("HTTP请求路径时错误：" + url, e.getMessage());
        throw e; // 异常外抛
    } finally {
        if (null != method)
            method.releaseConnection();
    }
    return jsonString;
}

POST请求我们使用URLConnection来写：

public static String sendPost(String url, String param)  throws Exception{
    PrintWriter out = null;
    BufferedReader in = null;
    String result = "";
    try {
        URL realUrl = new URL(url);
        URLConnection conn = realUrl.openConnection();
        conn.setConnectTimeout(5000);
        conn.setReadTimeout(10*1000);
        conn.setDoOutput(true); // 发送POST请求必须设置如下两行
        conn.setDoInput(true);
        out = new PrintWriter(conn.getOutputStream());
        out.print(param);
        out.flush();
        in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        String line;
        while ((line = in.readLine()) != null) {
            result += line;
        }
    } catch (Exception e) {
        logger.error("HTTP请求路径时错误：" + url, e.getMessage());
        throw e; // 异常外抛
    } finally{
        try{
            if(out!=null)out.close();
            if(in!=null) in.close();
        }
        catch(Exception ex){
        }
    }
    return result;
}

此时，同一个连接，调用不同的方法，就是不同的发送方式。

服务器端接收的话可以参照这样，基于SpringMVC的写法：

@SuppressWarnings({ "unchecked" })
@RequestMapping(value="/testPost2",method = RequestMethod.POST)
public ResponseEntity<String> testPost2(HttpServletRequest req,HttpServletResponse res,
        @RequestParam(value="postXML") String postXML) throws Exception{
    System.out.println(postXML);
     
    Document docRe = DocumentHelper.createDocument();
    Element SyncAppOrderResp = docRe.addElement("reXML").addNamespace("",
"http://www.javacui.com/xml/schemas/");
    SyncAppOrderResp.addElement("status").addText("0");
    return new ResponseEntity(docRe.asXML(), HttpStatus.OK);
}

以上的写法，POST的参数是基于KEY和VALUE方式的，还有一种普遍做法是把参数XML直接写在头里面。

此时的写法就是把要发送的参数写在RequestBody里面，执行发送的内容是基于什么格式的，例如下面的示例，普通发送，JSON和XML：

/**
 * 普通POST请求
 */
@SuppressWarnings("deprecation")
public static String HttpPost(String url, String body)  throws Exception{
    String jsonString = "";
    HttpClient client = new HttpClient(new HttpClientParams(), 
new SimpleHttpConnectionManager(true));
    client.getHttpConnectionManager().getParams().setConnectionTimeout(15000); 
//通过网络与服务器建立连接的超时时间
    client.getHttpConnectionManager().getParams().setSoTimeout(60000); 
//Socket读数据的超时时间，即从服务器获取响应数据需要等待的时间
    PostMethod method = new PostMethod(url);
    method.setRequestHeader("Content-Type", "text/html;charset=UTF-8");
    method.setRequestBody(body);
    try {
        client.executeMethod(method);
        jsonString = method.getResponseBodyAsString();
    } catch (Exception e) {
        jsonString = "error";
        logger.error("HTTP请求路径时错误：" + url, e.getMessage());
        throw e; // 异常外抛
    } finally {
        if (null != method)
            method.releaseConnection();
    }
    return jsonString;
}
/**
 * JSON的POST请求
 */
@SuppressWarnings("deprecation")
public static String HttpPostJSON(String url, JSONObject body)  throws Exception{
    String jsonString = "";
    HttpClient client = new HttpClient(new HttpClientParams(), 
new SimpleHttpConnectionManager(true));
    client.getHttpConnectionManager().getParams().setConnectionTimeout(15000); 
//通过网络与服务器建立连接的超时时间
    client.getHttpConnectionManager().getParams().setSoTimeout(60000); 
//Socket读数据的超时时间，即从服务器获取响应数据需要等待的时间
    client.getHttpConnectionManager().getParams().setParameter(
HttpMethodParams.HTTP_CONTENT_CHARSET, "UTF-8");
    PostMethod method = new PostMethod(url);
    method.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
    method.setRequestBody(body.toString());
    try {
        client.executeMethod(method);
        jsonString = method.getResponseBodyAsString();
    } catch (Exception e) {
        jsonString = "error";
        logger.error("HTTP请求路径时错误：" + url, e.getMessage());
        throw e; // 异常外抛
    } finally {
        if (null != method)
            method.releaseConnection();
    }
    return jsonString;
}
/**
 * XML的POST请求
 */
@SuppressWarnings("deprecation")
public static String HttpPostXml(String url, String xmlBody)  throws Exception{
    String result = "";
    HttpClient client = new HttpClient(new HttpClientParams(), 
new SimpleHttpConnectionManager(true));
    client.getHttpConnectionManager().getParams().setConnectionTimeout(15000); 
//通过网络与服务器建立连接的超时时间
    client.getHttpConnectionManager().getParams().setSoTimeout(60000); 
//Socket读数据的超时时间，即从服务器获取响应数据需要等待的时间
    PostMethod method = new PostMethod(url);
    method.setRequestHeader("Content-Type", "application/xml");
    if(null != xmlBody){
        method.setRequestBody(xmlBody);
    }
    try {
        client.executeMethod(method);
        result = method.getResponseBodyAsString();
    } catch (Exception e) {
        result = "error";
        logger.error("HTTP请求路径时错误：" + url, e.getMessage());
        throw e; // 异常外抛
    } finally {
        if (null != method)
            method.releaseConnection();
    }
    return result;
}

而服务器端接收时，就需要从头中获取参数，代码参考：

@SuppressWarnings({ "unchecked" })
@RequestMapping(value="/testPost1",method = RequestMethod.POST)
public ResponseEntity<String> testPost1(HttpServletRequest req,HttpServletResponse res) 
throws Exception{
    BufferedReader bufferReader = req.getReader();//获取头部参数信息
    StringBuffer buffer = new StringBuffer();
    String line = " ";
    while ((line = bufferReader.readLine()) != null) {
        buffer.append(line);
    }
    String postData = buffer.toString();
    System.out.println(postData);
     
    Document docRe = DocumentHelper.createDocument();
    Element SyncAppOrderResp = docRe.addElement("reXML").addNamespace("",
"http://www.javacui.com/xml/schemas/");
    SyncAppOrderResp.addElement("status").addText("0");
    return new ResponseEntity(docRe.asXML(), HttpStatus.OK);
}

testPost1和testPost2这两种方式，我们可以写一个MAIN来测试：

public static void main(String[] args) {
    try {
        System.out.println(HttpPostXml("http://localhost:8008/api/testPost1",
                "<?xml version=\\"1.0\\" encoding=\\"UTF-8\\"?><root><status>1
</status></root>"));
        System.out.println(sendPost("http://localhost:8008/api/testPost2",
                "postXML=<?xml version=\\"1.0\\" encoding=\\"UTF-8\\"?><root>
<status>1</status></root>"));
    } catch (Exception e) {
        e.printStackTrace();
    }
}

发送接收的都是XML参数，发送和接收打印在控制台。

文章参考地址：java小强个人博客站点