Adding appendHex method to StringBuilder

[Claes Redestad]

It’s possible to build up and combine unprocessed RAW template snippets, then combine and process them together:


static int[] val = new int[] { 2048, 31337, 0xbeefcace, 9000, 4711, 1337, 2100, 2600 };
@Benchmark
public String toStringFMTCombineHex8() {
    var templates = new ArrayList<StringTemplate>();
    for (int i = 0; i < 8; i++) {
        int h = val[i];
        templates.add(RAW."%x\{h}");
    }
    return StringTemplate.combine(templates).process(FMT);
}

Performance is… not great, but I think we can and should work on that:

Benchmark                                  Mode  Cnt     Score     Error  Units
StringBuilders.toStringFMTCombineHex8      avgt   15  2421,151 ± 646,501  ns/op

/Claes

2 okt. 2023 kl. 14:46 skrev 温绍锦(高铁) <shaojin.wensj at alibaba-inc.com>:

Using String Template FMT has better performance and better code readability. But String Template does not yet support for/while/if/switch. Is there any plan to enhance String Template to support for/while/if/switch? The following scenarios cannot be implemented using String.format or String Template. I think whether to build in support for foo(bar(x)) depends on whether it is a common enough method.

```java
package java.net;
class Inet6Address extends InetAddress {
    static String numericToTextFormat(byte[] src) {
        StringBuilder sb = new StringBuilder(39);
        for (int i = 0; i < (INADDRSZ / INT16SZ); i++) {
            sb.append(Integer.toHexString(((src[i<<1]<<8) & 0xff00)
                                          | (src[(i<<1)+1] & 0xff)));
            if (i < (INADDRSZ / INT16SZ) -1 ) {
              sb.append(":");
            }
        }
        return sb.toString();
    }
}
class SocketPermission {
  private boolean authorizedIPv6(String cname, byte[] addr) {
        String authHost = "";
        InetAddress auth;
        try {
            StringBuilder sb = new StringBuilder(39);
            for (int i = 15; i >= 0; i--) {
                sb.append(Integer.toHexString(((addr[i]) & 0x0f)));
                sb.append('.');
                sb.append(Integer.toHexString(((addr[i] >> 4) & 0x0f)));
                sb.append('.');
            }
        ...
  }
}
```
```java
package sun.security.krb5.internal.crypto.dk;
class DkCrypto {
    static String bytesToString(byte[] digest) {
        // Get character representation of digest
        StringBuilder digestString = new StringBuilder();
        for (int i = 0; i < digest.length; i++) {
            if ((digest[i] & 0x000000ff) < 0x10) {
                digestString.append('0').append(Integer.toHexString(digest[i] & 0x000000ff));
            } else {
                digestString.append(
                    Integer.toHexString(digest[i] & 0x000000ff));
            }
        }
        return digestString.toString();
    }
}
```

- wenshao

------------------------------------------------------------------
发件人：Mark Reinhold <mark.reinhold at oracle.com>
发送时间：2023年10月2日(星期一) 20:19
收件人：Claes Redestad <claes.redestad at oracle.com>
抄　送：温绍锦(高铁) <shaojin.wensj at alibaba-inc.com>; core-libs-dev at openjdk.org <core-libs-dev at openjdk.org>
主　题：Re: Adding appendHex method to StringBuilder

2023/10/2 7:22:55 -0400, claes.redestad at oracle.com:
> I think this goes against the grain: StringBuilder is a simple builder
> for non-localized unformatted output. For formatted output there’s
> Formatter, String.format and, with JEP 430[1], FMT."..." to help output
> string data in more advanced, formatted and localized ways.

Agreed.

If we were to introduce a `fooBar(x)` method for every common
`foo(bar(x))` expression in the JDK code base then our APIs
would fast become inscrutable.

- Mark


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