试试下面的方法:

添加一个新的依赖项

<!-- https://mvnrepository.com/artifact/org.apache.tomcat/tomcat-catalina -->
<dependency>
    <groupId>org.apache.tomcat</groupId>
    <artifactId>tomcat-catalina</artifactId>
    <version>10.0.13</version>
</dependency>

现在按照下面的步骤做:

String str = "Hello+World"; // For "Hello World", decoder is not required
// import java.net.URLDecoder;
String newURL = URLDecoder.decode(str, StandardCharsets.UTF_8);
// import org.apache.catalina.util.URLEncoder;
System.out.println(URLEncoder.DEFAULT.encode(newURL, StandardCharsets.UTF_8));

你会得到如下的输出:

Hello%20World

使用MyUrlEncode。URLencoding(String url, String enc)来处理这个问题

    public class MyUrlEncode {
    static BitSet dontNeedEncoding = null;
    static final int caseDiff = ('a' - 'A');
    static {
        dontNeedEncoding = new BitSet(256);
        int i;
        for (i = 'a'; i <= 'z'; i++) {
            dontNeedEncoding.set(i);
        }
        for (i = 'A'; i <= 'Z'; i++) {
            dontNeedEncoding.set(i);
        }
        for (i = '0'; i <= '9'; i++) {
            dontNeedEncoding.set(i);
        }
        dontNeedEncoding.set('-');
        dontNeedEncoding.set('_');
        dontNeedEncoding.set('.');
        dontNeedEncoding.set('*');
        dontNeedEncoding.set('&');
        dontNeedEncoding.set('=');
    }
    public static String char2Unicode(char c) {
        if(dontNeedEncoding.get(c)) {
            return String.valueOf(c);
        }
        StringBuffer resultBuffer = new StringBuffer();
        resultBuffer.append("%");
        char ch = Character.forDigit((c >> 4) & 0xF, 16);
            if (Character.isLetter(ch)) {
            ch -= caseDiff;
        }
        resultBuffer.append(ch);
            ch = Character.forDigit(c & 0xF, 16);
            if (Character.isLetter(ch)) {
            ch -= caseDiff;
        }
         resultBuffer.append(ch);
        return resultBuffer.toString();
    }
    private static String URLEncoding(String url,String enc) throws UnsupportedEncodingException {
        StringBuffer stringBuffer = new StringBuffer();
        if(!dontNeedEncoding.get('/')) {
            dontNeedEncoding.set('/');
        }
        if(!dontNeedEncoding.get(':')) {
            dontNeedEncoding.set(':');
        }
        byte [] buff = url.getBytes(enc);
        for (int i = 0; i < buff.length; i++) {
            stringBuffer.append(char2Unicode((char)buff[i]));
        }
        return stringBuffer.toString();
    }
    private static String URIEncoding(String uri , String enc) throws UnsupportedEncodingException { //对请求参数进行编码
        StringBuffer stringBuffer = new StringBuffer();
        if(dontNeedEncoding.get('/')) {
            dontNeedEncoding.clear('/');
        }
        if(dontNeedEncoding.get(':')) {
            dontNeedEncoding.clear(':');
        }
        byte [] buff = uri.getBytes(enc);
        for (int i = 0; i < buff.length; i++) {
            stringBuffer.append(char2Unicode((char)buff[i]));
        }
        return stringBuffer.toString();
    }

    public static String URLencoding(String url , String enc) throws UnsupportedEncodingException {
        int index = url.indexOf('?');
        StringBuffer result = new StringBuffer();
        if(index == -1) {
            result.append(URLEncoding(url, enc));
        }else {
            result.append(URLEncoding(url.substring(0 , index),enc));
            result.append("?");
            result.append(URIEncoding(url.substring(index+1),enc));
        }
        return result.toString();
    }

}

只是在Android上也在挣扎，设法偶然发现了Uri。encode(字符串，字符串)而特定于android (android.net.Uri)可能对一些有用。

静态字符串编码(字符串s，字符串允许)

以https://developer.android.com/reference/android/net/Uri.html编码(以)

这是预期的行为。URLEncoder实现了如何在HTML表单中编码url的HTML规范。

来自javadocs:

该类包含的静态方法 将String转换为 应用程序/ x-www-form-urlencoded MIME 格式。

和来自HTML规范:

应用程序/ x-www-form-urlencoded 使用此内容类型提交的表单 必须编码如下: 控件名称和值被转义。空格字符被替换 通过“+”

你必须更换它，例如:

System.out.println(java.net.URLEncoder.encode("Hello World", "UTF-8").replace("+", "%20"));

它不是一行代码，但是你可以使用:

URL url = new URL("https://some-host.net/dav/files/selling_Rosetta Stone Case Study.png.aes");
URI uri = new URI(url.getProtocol(), url.getUserInfo(), url.getHost(), url.getPort(), url.getPath(), url.getQuery(), url.getRef());
System.out.println(uri.toString());

这将给你一个输出:

https://some-host.net/dav/files/selling_Rosetta%20Stone%20Case%20Study.png.aes

“+”是正确的。如果你真的需要%20，然后自己替换加。

警告:这个答案有很大的争议(+8 vs. -6)，所以对这个答案持保留态度。