HttpURLConnection使用
URLConnection是JDK提供的网络请求的APi。URLConnection是一个抽象类，在实际使用中，我们创建它的子类HttpURLConnection的实例来进行网络请求。
1.HttpUrlConnection基本使用
调用URL的openConnection方法来创建实例。
| HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
|
常用方法
| // 设置连接超时时间
connection.setConnectTimeout(CONNECT_TIMEOUT);
// 设置读取超时时间
connection.setReadTimeout(READ_TIMEOUT);
//设置是否向HttpURLConnection输出，Post请求参数要放在正文中，因此需要设为true，默认情况为false。
connection.setDoOutput(true);
//设置是否从HttpURLConnection输入，默认情况下true
connection.setDoInput(true);
//设置请求方法
connection.setRequestMethod("POST");
//添加请求头
connection.addRequestProperty("Content-Length", "106512");
|
2.示例
接下来我们将用实例来演示HttpUrlConnection的用法
2.1Get请求
略
2.2Post请求
| public static String postRequest(String url, Map<String, String> headers, Map<String, String> params) {
try {
HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
connection.setConnectTimeout(CONNECT_TIMEOUT);
connection.setReadTimeout(READ_TIMEOUT);
connection.setDoOutput(true);
connection.setDoInput(true);
connection.setRequestMethod("POST");
connection.connect();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
if (headers != null) {
Set<String> keys = headers.keySet();
Iterator<String> iterator = keys.iterator();
while (iterator.hasNext()) {
String key = iterator.next();
String value = params.get(key);
// 添加请求头
connection.addRequestProperty(key, value);
}
}
if (params != null) {
Set<String> keys = params.keySet();
Iterator<String> iterator = keys.iterator();
while (iterator.hasNext()) {
String key = iterator.next();
String value = params.get(key);
if (baos.size() > 0) {
baos.write('&');
}
baos.write(URLEncoder.encode(key, "UTF-8").getBytes("UTF-8"));
baos.write('=');
baos.write(URLEncoder.encode(value, "UTF-8").getBytes("UTF-8"));
}
}
OutputStream os = connection.getOutputStream();
os.write(baos.toByteArray());
int status = connection.getResponseCode();
InputStream is;
if (status >= 400) {
is = connection.getErrorStream();
} else {
is = connection.getInputStream();
}
InputStreamReader isr = new InputStreamReader(is);
BufferedReader bufr = new BufferedReader(isr);
String line;
StringBuilder sb = new StringBuilder();
while ((line = bufr.readLine()) != null) {
sb.append(line);
}
return sb.toString();
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
|
2.3文件上传
从普通的web页面上传文件很简单，只需要在form标签标上enctype="multipart/form-data"即可，浏览器将自动完成数据收集并发送Http请求。由于脱离了浏览器的环境，我们就要自己去完成数据的收集并发送请求。首先我们写一个JSP页面来看看浏览器是如何发送Http请求的。
| <html>
<head>
<meta charset="UTF-8">
<title>TestSubmit</title>
</head>
<body>
<form name="upform" action="upload.do" method="POST" enctype="multipart/form-data">
参数<input type="text" name="username"/><br/>
文件1<input type="file" name="file1"/><br/>
文件2<input type="file" name="file2"/><br/>
<input type="submit" value="Submit" /><br/>
</form>
</body>
</html>
|
form提交的信息如下。
| -----------------------------7da2e536604c8
Content-Disposition: form-data; name="username"
hello word
-----------------------------7da2e536604c8
Content-Disposition: form-data; name="file1"; filename="D:/haha.txt"
Content-Type: text/plain
haha
hahaha
-----------------------------7da2e536604c8
Content-Disposition: form-data; name="file2"; filename="D:/huhu.txt"
Content-Type: text/plain
messi
huhu
-----------------------------7da2e536604c8--
|
我们只要模拟这个数据，并写入Http请求中就能实现文件的上传。
构建分割线
| private static byte[] buildBoundary(String boundary, boolean first, boolean last) {
try {
StringBuilder sb = new StringBuilder(boundary.length() + 8);
if (!first) {//不是第一行进行换行
sb.append("\r\n");
}
sb.append("--");
sb.append(boundary);
if (last) {
sb.append("--");
}
sb.append("\r\n");
return sb.toString().getBytes("UTF-8");
} catch (IOException ex) {
}
}
|
构建请求头
| private static byte[] buildHeader(String name, Object value) {
try {
String transferEncoding = "binary";
StringBuilder headers = new StringBuilder(128);
headers.append("Content-Disposition: form-data; name=\"");
headers.append(name);
long length = 0;
if (value instanceof File) {
String fileName = ((File) value).getName();
if (fileName != null) {
headers.append("\"; filename=\"");
headers.append(fileName);
}
headers.append("\"\r\nContent-Type: ");
headers.append(URLConnection.guessContentTypeFromName(((File) value).getPath()));
length = ((File) value).length();
} else if (value instanceof String) {
headers.append("\"\r\nContent-Type: ");
headers.append("text/plain;charset=UTF-8");
length = ((String) value).getBytes().length;
}
if (length != -1) {
headers.append("\r\nContent-Length: ").append(length);
}
headers.append("\r\nContent-Transfer-Encoding: ");
headers.append(transferEncoding);
headers.append("\r\n\r\n");
return headers.toString().getBytes("UTF-8");
} catch (IOException ex) {
}
}
|
上传方法
| public static String upload(String url, Map<String, String> headers, Map<String, Object> params) {
try {
String BOUNDARY = UUID.randomUUID().toString();
HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
connection.setConnectTimeout(CONNECT_TIMEOUT);
connection.setReadTimeout(READ_TIMEOUT);
connection.setDoOutput(true);
connection.setDoInput(true);
connection.setRequestMethod("POST");
ByteArrayOutputStream baos = new ByteArrayOutputStream();
if (headers != null) {
Set<String> keys = headers.keySet();
Iterator<String> iterator = keys.iterator();
while (iterator.hasNext()) {
String key = iterator.next();
String value = headers.get(key);
connection.addRequestProperty(key, value);
}
}
connection.addRequestProperty("Content-Type", "multipart/form-data; boundary=" + BOUNDARY);
boolean first = true;
if (params != null) {
Set<String> keys = params.keySet();
Iterator<String> iterator = keys.iterator();
while (iterator.hasNext()) {
String key = iterator.next();
Object value = params.get(key);
baos.write(buildBoundary(BOUNDARY, first, false));
baos.write(buildHeader(key, value));
first = false;
if (value instanceof String) {
baos.write((value + "\r\n").getBytes("UTF-8"));
} else if (value instanceof File) {
FileInputStream fis = new FileInputStream((File) value);
byte[] bytes = new byte[4096];
int hasRead;
while ((hasRead = fis.read(bytes)) != -1) {
baos.write(bytes, 0, hasRead);
}
}
}
}
baos.write(buildBoundary(BOUNDARY, first, true));
OutputStream os = connection.getOutputStream();
os.write(baos.toByteArray());
int status = connection.getResponseCode();
InputStream is;
if (status >= 400) {
is = connection.getErrorStream();
} else {
is = connection.getInputStream();
}
InputStreamReader isr = new InputStreamReader(is);
BufferedReader bufr = new BufferedReader(isr);
String line;
StringBuilder sb = new StringBuilder();
while ((line = bufr.readLine()) != null) {
sb.append(line);
}
return sb.toString();
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
|