疑问

1. 空格变成了+？
2. -*.不能转换url编码？

解惑

1. URL 编码通常使用加号（+）或 %20 替代空格。
   如果要转换为%20，可以先进行转换编码，再替换 + 为 %20
   注意：在JavaScript中，空格被编码成%20

     //解决urlecode空格问题
    String message = "我是空  格";
    System.out.println(URLEncoder.encode(message, "UTF-8").replace("+","%20"));
    System.out.println(URLDecoder.decode(URLEncoder.encode(message, "UTF-8"), "UTF-8"));

1. 同样将 -*. 替换成响应的URL编码

// . -> %2E
// * -> %2A
// - -> %2D
URLEncoder.encode(message, "UTF-8").replace(".","%2E").replace("*","%2A").replace("-","%2D")

只转变汉字

public class URLtoUTF8 {
    //转换为url编码
    public static String toUtf8String(String s) {
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c >= 0 && c <= 255) {
                sb.append(c);
            } else {
                byte[] b;
                try {
                    b = String.valueOf(c).getBytes("utf-8");
                } catch (Exception ex) {
                    System.out.println(ex);
                    b = new byte[0];
                }
                for (int j = 0; j < b.length; j++) {
                    int k = b[j];
                    if (k < 0)
                        k += 256;
                    sb.append("%" + Integer.toHexString(k).toUpperCase());
                }
            }
        }
        return sb.toString();
    }
    //将url编码转换为汉字 
    public static String unescape(String s) {
        StringBuffer sbuf = new StringBuffer();
        int l = s.length();
        int ch = -1;
        int b, sumb = 0;
        for (int i = 0, more = -1; i < l; i++) {
            /* Get next byte b from URL segment s */
            switch (ch = s.charAt(i)) {
            case '%':
                ch = s.charAt(++i);
                int hb = (Character.isDigit((char) ch) ? ch - '0'
                        : 10 + Character.toLowerCase((char) ch) - 'a') & 0xF;
                ch = s.charAt(++i);
                int lb = (Character.isDigit((char) ch) ? ch - '0'
                        : 10 + Character.toLowerCase((char) ch) - 'a') & 0xF;
                b = (hb << 4) | lb;
                break;
            case '+':
                b = ' ';
                break;
            default:
                b = ch;
            }
            /* Decode byte b as UTF-8, sumb collects incomplete chars */
            if ((b & 0xc0) == 0x80) { // 10xxxxxx (continuation byte)   
                sumb = (sumb << 6) | (b & 0x3f); // Add 6 bits to sumb   
                if (--more == 0)
                    sbuf.append((char) sumb); // Add char to sbuf   
            } else if ((b & 0x80) == 0x00) { // 0xxxxxxx (yields 7 bits)   
                sbuf.append((char) b); // Store in sbuf   
            } else if ((b & 0xe0) == 0xc0) { // 110xxxxx (yields 5 bits)   
                sumb = b & 0x1f;
                more = 1; // Expect 1 more byte   
            } else if ((b & 0xf0) == 0xe0) { // 1110xxxx (yields 4 bits)   
                sumb = b & 0x0f;
                more = 2; // Expect 2 more bytes   
            } else if ((b & 0xf8) == 0xf0) { // 11110xxx (yields 3 bits)   
                sumb = b & 0x07;
                more = 3; // Expect 3 more bytes   
            } else if ((b & 0xfc) == 0xf8) { // 111110xx (yields 2 bits)   
                sumb = b & 0x03;
                more = 4; // Expect 4 more bytes   
            } else /*if ((b & 0xfe) == 0xfc)*/{ // 1111110x (yields 1 bit)   
                sumb = b & 0x01;
                more = 5; // Expect 5 more bytes   
            }
            /* We don't test if the UTF-8 encoding is well-formed */
        }
        return sbuf.toString();
    }

    public static void main(String[] args){
        System.out.println(URLtoUTF8.toUtf8String("你"));
        System.out.println(URLtoUTF8.unescape("%E4%BD%A0%20%E5%A5%BD"));

    }
}

参考

HTML URL 编码参考手册