如何通過Java發(fā)送HTTP請(qǐng)求，通俗點(diǎn)講，如何通過Java（模擬瀏覽器）發(fā)送HTTP請(qǐng)求。

Java有原生的API可用于發(fā)送HTTP請(qǐng)求，即java.net.URL、java.net.URLConnection，這些API很好用、很常用，但不夠簡(jiǎn)便；

所以，也流行有許多Java HTTP請(qǐng)求的framework，如，Apache的HttpClient。

目前項(xiàng)目主要用到Java原生的方式，所以，這里主要介紹此方式。

二、運(yùn)用原生Java Api發(fā)送簡(jiǎn)單的Get請(qǐng)求、Post請(qǐng)求步驟

1.通過統(tǒng)一資源定位器（java.net.URL）獲取連接器（java.net.URLConnection）

2.設(shè)置請(qǐng)求的參數(shù)

3.發(fā)送請(qǐng)求

4.以輸入流的形式獲取返回內(nèi)容

5.關(guān)閉輸入流

三、發(fā)送請(qǐng)求與接收響應(yīng)流類 HttpRequestor

package me.http; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.OutputStream; import java.io.OutputStreamWriter; import java.net.HttpURLConnection; import java.net.InetSocketAddress; import java.net.Proxy; import java.net.URL; import java.net.URLConnection; import java.util.Iterator; import java.util.Map; public class HttpRequestor { private String charset = "utf-8"; private Integer connectTimeout = null; private Integer socketTimeout = null; private String proxyHost = null; private Integer proxyPort = null; /** * Do GET request * @param url * @return * @throws Exception * @throws IOException */ public String doGet(String url) throws Exception { URL localURL = new URL(url); URLConnection connection = this.openConnection(localURL); HttpURLConnection httpURLConnection = (HttpURLConnection)connection; httpURLConnection.setRequestProperty("Accept-Charset", charset); httpURLConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); InputStream inputStream = null; InputStreamReader inputStreamReader = null; BufferedReader reader = null; StringBuffer resultBuffer = new StringBuffer(); String tempLine = null; //響應(yīng)失敗 if (httpURLConnection.getResponseCode() >= 300) { throw new Exception("HTTP Request is not success, Response code is " + httpURLConnection.getResponseCode()); } try { inputStream = httpURLConnection.getInputStream(); inputStreamReader = new InputStreamReader(inputStream); reader = new BufferedReader(inputStreamReader); while ((tempLine = reader.readLine()) != null) { resultBuffer.append(tempLine); } } finally { if (reader != null) { reader.close(); } if (inputStreamReader != null) { inputStreamReader.close(); } if (inputStream != null) { inputStream.close(); } } return resultBuffer.toString(); } /** * Do POST request * @param url * @param parameterMap * @return * @throws Exception */ public String doPost(String url, Map parameterMap) throws Exception { /* Translate parameter map to parameter date string */ StringBuffer parameterBuffer = new StringBuffer(); if (parameterMap != null) { Iterator iterator = parameterMap.keySet().iterator(); String key = null; String value = null; while (iterator.hasNext()) { key = (String)iterator.next(); if (parameterMap.get(key) != null) { value = (String)parameterMap.get(key); } else { value = ""; } parameterBuffer.append(key).append("=").append(value); if (iterator.hasNext()) { parameterBuffer.append("&"); } } } System.out.println("POST parameter : " + parameterBuffer.toString()); URL localURL = new URL(url); URLConnection connection = this.openConnection(localURL); HttpURLConnection httpURLConnection = (HttpURLConnection)connection; httpURLConnection.setDoOutput(true); httpURLConnection.setRequestMethod("POST"); httpURLConnection.setRequestProperty("Accept-Charset", charset); httpURLConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); httpURLConnection.setRequestProperty("Content-Length", String.valueOf(parameterBuffer.length())); OutputStream outputStream = null; OutputStreamWriter outputStreamWriter = null; InputStream inputStream = null; InputStreamReader inputStreamReader = null; BufferedReader reader = null; StringBuffer resultBuffer = new StringBuffer(); String tempLine = null; try { outputStream = httpURLConnection.getOutputStream(); outputStreamWriter = new OutputStreamWriter(outputStream); outputStreamWriter.write(parameterBuffer.toString()); outputStreamWriter.flush(); //響應(yīng)失敗 if (httpURLConnection.getResponseCode() >= 300) { throw new Exception("HTTP Request is not success, Response code is " + httpURLConnection.getResponseCode()); } //接收響應(yīng)流 inputStream = httpURLConnection.getInputStream(); inputStreamReader = new InputStreamReader(inputStream); reader = new BufferedReader(inputStreamReader); while ((tempLine = reader.readLine()) != null) { resultBuffer.append(tempLine); } } finally { if (outputStreamWriter != null) { outputStreamWriter.close(); } if (outputStream != null) { outputStream.close(); } if (reader != null) { reader.close(); } if (inputStreamReader != null) { inputStreamReader.close(); } if (inputStream != null) { inputStream.close(); } } return resultBuffer.toString(); } private URLConnection openConnection(URL localURL) throws IOException { URLConnection connection; if (proxyHost != null && proxyPort != null) { Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(proxyHost, proxyPort)); connection = localURL.openConnection(proxy); } else { connection = localURL.openConnection(); } return connection; } /** * Render request according setting * @param request */ private void renderRequest(URLConnection connection) { if (connectTimeout != null) { connection.setConnectTimeout(connectTimeout); } if (socketTimeout != null) { connection.setReadTimeout(socketTimeout); } } /* * Getter & Setter */ public Integer getConnectTimeout() { return connectTimeout; } public void setConnectTimeout(Integer connectTimeout) { this.connectTimeout = connectTimeout; } public Integer getSocketTimeout() { return socketTimeout; } public void setSocketTimeout(Integer socketTimeout) { this.socketTimeout = socketTimeout; } public String getProxyHost() { return proxyHost; } public void setProxyHost(String proxyHost) { this.proxyHost = proxyHost; } public Integer getProxyPort() { return proxyPort; } public void setProxyPort(Integer proxyPort) { this.proxyPort = proxyPort; } public String getCharset() { return charset; } public void setCharset(String charset) { this.charset = charset; } }

四、為測(cè)試方便,新建一個(gè)項(xiàng)目,并新建一個(gè)Servlet,接收post請(qǐng)求并對(duì)HttpRequestor請(qǐng)求響應(yīng),發(fā)出響應(yīng)流

LoginServlet.java代碼:此處使用了

注解: @WebServlet("/LoginServlet") ,也可以在web.xml配置Servlet