java调用Http请求 -HttpURLConnection学习

public class HttpInvoker {

    public static final String GET_URL = "http://localhost:8080/welcome1";

    public static final String POST_URL = "http://localhost:8080/welcome1";

    public static void readContentFromGet() throws IOException {
        // 拼凑get请求的URL字串，使用URLEncoder.encode对特殊和不可见字符进行编码
        String getURL = GET_URL + "?username="
                + URLEncoder.encode("fat man", "utf-8");
        URL getUrl = new URL(getURL);
        // 根据拼凑的URL，打开连接，URL.openConnection函数会根据URL的类型，
        // 返回不同的URLConnection子类的对象，这里URL是一个http，因此实际返回的是HttpURLConnection
        HttpURLConnection connection = (HttpURLConnection) getUrl
                .openConnection();
        // 进行连接，但是实际上get request要在下一句的connection.getInputStream()函数中才会真正发到
        // 服务器
        connection.connect();
        // 取得输入流，并使用Reader读取
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                connection.getInputStream()));
        System.out.println("=============================");
        System.out.println("Contents of get request");
        System.out.println("=============================");
        String lines;
        while ((lines = reader.readLine()) != null) {
            System.out.println(lines);
        }
        reader.close();
        // 断开连接
        connection.disconnect();
        System.out.println("=============================");
        System.out.println("Contents of get request ends");
        System.out.println("=============================");
    }

    public static void readContentFromPost() throws IOException {
        // Post请求的url，与get不同的是不需要带参数
        URL postUrl = new URL(POST_URL);
        // 打开连接
        HttpURLConnection connection = (HttpURLConnection) postUrl
                .openConnection();
        // Output to the connection. Default is
        // false, set to true because post
        // method must write something to the
        // connection
        // 设置是否向connection输出，因为这个是post请求，参数要放在
        // http正文内，因此需要设为true
        connection.setDoOutput(true);
        // Read from the connection. Default is true.
        connection.setDoInput(true);
        // Set the post method. Default is GET
        connection.setRequestMethod("POST");
        // Post cannot use caches
        // Post 请求不能使用缓存
        connection.setUseCaches(false);
        // This method takes effects to
        // every instances of this class.
        // URLConnection.setFollowRedirects是static函数，作用于所有的URLConnection对象。
        // connection.setFollowRedirects(true);

        // This methods only
        // takes effacts to this
        // instance.
        // URLConnection.setInstanceFollowRedirects是成员函数，仅作用于当前函数
        connection.setInstanceFollowRedirects(true);
        // Set the content type to urlencoded,
        // because we will write
        // some URL-encoded content to the
        // connection. Settings above must be set before connect!
        // 配置本次连接的Content-type，配置为application/x-www-form-urlencoded的
        // 意思是正文是urlencoded编码过的form参数，下面我们可以看到我们对正文内容使用URLEncoder.encode
        // 进行编码
        connection.setRequestProperty("Content-Type",
                "application/x-www-form-urlencoded");
        // 连接，从postUrl.openConnection()至此的配置必须要在connect之前完成，
        // 要注意的是connection.getOutputStream会隐含的进行connect。
        connection.connect();
        DataOutputStream out = new DataOutputStream(connection
                .getOutputStream());
        // The URL-encoded contend
        // 正文，正文内容其实跟get的URL中‘?‘后的参数字符串一致
        String content = "firstname=" + URLEncoder.encode("一个大肥人", "utf-8");
        // DataOutputStream.writeBytes将字符串中的16位的unicode字符以8位的字符形式写道流里面
        out.writeBytes(content); 

        out.flush();
        out.close(); // flush and close
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                connection.getInputStream()));
        String line;
        System.out.println("=============================");
        System.out.println("Contents of post request");
        System.out.println("=============================");
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
        System.out.println("=============================");
        System.out.println("Contents of post request ends");
        System.out.println("=============================");
        reader.close();
        connection.disconnect();
    }

    /** *//**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        try {
            readContentFromGet();
            readContentFromPost();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

public static void readContentFromChunkedPost() throws IOException {
        URL postUrl = new URL(POST_URL);
        HttpURLConnection connection = (HttpURLConnection) postUrl
                .openConnection();
        connection.setDoOutput(true);
        connection.setDoInput(true);
        connection.setRequestMethod("POST");
        connection.setUseCaches(false);
        connection.setInstanceFollowRedirects(true);
        connection.setRequestProperty("Content-Type",
                "application/x-www-form-urlencoded");
        /**//*
         * 与readContentFromPost()最大的不同，设置了块大小为5字节
         */
        connection.setChunkedStreamingMode(5);
        connection.connect();
        /**//*
         * 注意，下面的getOutputStream函数工作方式于在readContentFromPost()里面的不同
         * 在readContentFromPost()里面该函数仍在准备http request，没有向服务器发送任何数据
         * 而在这里由于设置了ChunkedStreamingMode，getOutputStream函数会根据connect之前的配置
         * 生成http request头，先发送到服务器。
         */
        DataOutputStream out = new DataOutputStream(connection
                .getOutputStream());
        String content = "firstname=" + URLEncoder.encode("一个大肥人                                                                               " +
                "                                          " +
                "asdfasfdasfasdfaasdfasdfasdfdasfs", "utf-8");
        out.writeBytes(content); 

        out.flush();
        out.close(); // 到此时服务器已经收到了完整的http request了，而在readContentFromPost()函数里，要等到下一句服务器才能收到http请求。
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                connection.getInputStream()));
        
        out.flush();
        out.close(); // flush and close
        String line;
        System.out.println("=============================");
        System.out.println("Contents of post request");
        System.out.println("=============================");
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
        System.out.println("=============================");
        System.out.println("Contents of post request ends");
        System.out.println("=============================");
        reader.close();
        connection.disconnect();
    }