我把上面的内容做了一些改变。我首先喜欢正逻辑，并且我认为HashSet可能比其他选项(比如通过String进行搜索)提供更好的性能。虽然，我不确定自动装箱的代价是否值得，但如果编译器针对ASCII字符进行了优化，那么装箱的代价就会很低。

/***
 * Replaces any character not specifically unreserved to an equivalent 
 * percent sequence.
 * @param s
 * @return
 */
public static String encodeURIcomponent(String s)
{
    StringBuilder o = new StringBuilder();
    for (char ch : s.toCharArray()) {
        if (isSafe(ch)) {
            o.append(ch);
        }
        else {
            o.append('%');
            o.append(toHex(ch / 16));
            o.append(toHex(ch % 16));
        }
    }
    return o.toString();
}

private static char toHex(int ch)
{
    return (char)(ch < 10 ? '0' + ch : 'A' + ch - 10);
}

// https://tools.ietf.org/html/rfc3986#section-2.3
public static final HashSet<Character> UnreservedChars = new HashSet<Character>(Arrays.asList(
        'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
        'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
        '0','1','2','3','4','5','6','7','8','9',
        '-','_','.','~'));
public static boolean isSafe(char ch)
{
    return UnreservedChars.contains(ch);
}

请注意，上面的大部分答案都是不正确的。

URLEncoder类，不管它的名字，不是这里需要的。不幸的是，Sun给这个类命名得如此烦人。URLEncoder用于作为参数传递数据，而不是用于对URL本身进行编码。

换句话说，“http://search.barnesandnoble.com/booksearch/first book.pdf”是URL。参数可以是，例如，“http://search.barnesandnoble.com/booksearch/first book.pdf?parameter1=this&param2=that”。参数是你使用URLEncoder的目的。

下面两个例子强调了两者之间的区别。

根据HTTP标准，下面会产生错误的参数。注意&号(&)和加号(+)编码错误。

uri = new URI("http", null, "www.google.com", 80, 
"/help/me/book name+me/", "MY CRZY QUERY! +&+ :)", null);

// URI: http://www.google.com:80/help/me/book%20name+me/?MY%20CRZY%20QUERY!%20+&+%20:)

下面的代码将生成正确的参数，并对查询进行正确编码。注意空格、&号和加号。

uri = new URI("http", null, "www.google.com", 80, "/help/me/book name+me/", URLEncoder.encode("MY CRZY QUERY! +&+ :)", "UTF-8"), null);

// URI: http://www.google.com:80/help/me/book%20name+me/?MY+CRZY+QUERY%2521+%252B%2526%252B+%253A%2529

也许可以试试org.springframework.web.util中的UriUtils

UriUtils.encodeUri(input, "UTF-8")

uri类可以提供帮助;你可以在URL的文档中找到

注意，URI类在某些情况下确实执行组件字段的转义。建议使用URI来管理url的编码和解码

使用一个具有多个参数的构造函数，例如:

URI uri = new URI(
    "http", 
    "search.barnesandnoble.com", 
    "/booksearch/first book.pdf",
    null);
URL url = uri.toURL();
//or String request = uri.toString();

(URI的单参数构造函数不转义非法字符)

上面的代码只转义了非法字符——它不会转义非ascii字符(参见fatih的评论)。 toASCIIString方法可用于获取仅包含US-ASCII字符的String:

URI uri = new URI(
    "http", 
    "search.barnesandnoble.com", 
    "/booksearch/é",
    null);
String request = uri.toASCIIString();

对于像http://www.google.com/ig/api?weather=São Paulo这样的查询URL，使用构造函数的5个参数版本:

URI uri = new URI(
        "http", 
        "www.google.com", 
        "/ig/api",
        "weather=São Paulo",
        null);
String request = uri.toASCIIString();

如果你的URL中有一个编码的“/”(%2F)，这仍然是一个问题。

RFC 3986 -章节2.2说:“如果URI组件的数据与保留字符作为分隔符的目的相冲突，那么冲突的数据必须在URI形成之前进行百分比编码。”(rfc3986 -第2.2节)

但是Tomcat有一个问题:

http://tomcat.apache.org/security-6.html - Fixed in Apache Tomcat 6.0.10 important: Directory traversal CVE-2007-0450 Tomcat permits '\', '%2F' and '%5C' [...] . The following Java system properties have been added to Tomcat to provide additional control of the handling of path delimiters in URLs (both options default to false): org.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH: true|false org.apache.catalina.connector.CoyoteAdapter.ALLOW_BACKSLASH: true|false Due to the impossibility to guarantee that all URLs are handled by Tomcat as they are in proxy servers, Tomcat should always be secured as if no proxy restricting context access was used. Affects: 6.0.0-6.0.9

因此，如果您有一个含有%2F字符的URL, Tomcat将返回:"400 Invalid URI: noSlash"

你可以在Tomcat启动脚本中切换bug修复:

set JAVA_OPTS=%JAVA_OPTS% %LOGGING_CONFIG%   -Dorg.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH=true 

你可以使用这样的函数。根据您的需要完成并修改:

/**
     * Encode URL (except :, /, ?, &, =, ... characters)
     * @param url to encode
     * @param encodingCharset url encoding charset
     * @return encoded URL
     * @throws UnsupportedEncodingException
     */
    public static String encodeUrl (String url, String encodingCharset) throws UnsupportedEncodingException{
            return new URLCodec().encode(url, encodingCharset).replace("%3A", ":").replace("%2F", "/").replace("%3F", "?").replace("%3D", "=").replace("%26", "&");
    }

使用示例:

String urlToEncode = ""http://www.growup.com/folder/intérieur-à_vendre?o=4";
Utils.encodeUrl (urlToEncode , "UTF-8")

结果是:http://www.growup.com/folder/int%C3%A9rieur-%C3%A0_vendre?o=4