Parse a URI String into Name-Value Collection

Navigating complex URI structures

Invoking Java 8 features for elegance

Java 8's Streams API simplifies parsing of URI query strings. It effectively means you're cool and modern:

import java.net.URI;
import java.util.Map;
import java.util.stream.Collectors;

// ...

URI uri = new URI("http://example.com/?param1=value1&param2=");
Map<String, List<String>> query_pairs = 
    URLEncodedUtils.parse(uri, StandardCharsets.UTF_8).stream()
        .collect(Collectors.groupingBy(
            NameValuePair::getName,
            Collectors.mapping(NameValuePair::getValue, Collectors.toList())
        ));
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Highlights:

• Dealing with same keys having multiple values. Yes, it happens.
• Stream actions for clever and readable parsing. You're doing it, Peter!

Tricky URI scenarios like a pro

Empty values or repeating keys can bring eyebrows together. Here's a strategy:

// ...
Map<String, List<String>> query_pairs = new LinkedHashMap<>();
String query = uri.getQuery();
if (query != null) {
    for (String pair : query.split("&")) {
        int idx = pair.indexOf("=");
        query_pairs.computeIfAbsent(
            URLDecoder.decode(pair.substring(0, idx), StandardCharsets.UTF_8.name()),
            k -> new ArrayList<>()
        ).add(idx > 0 && pair.length() > idx + 1
            ? URLDecoder.decode(pair.substring(idx + 1), StandardCharsets.UTF_8.name()) 
            : null);
    }
}
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Key takeaways:

• LinkedHashMap preserves parsing order. Order! Order!
• URLDecoder handles URL encoding. Yeah, those %20s? They’re spaces!
• A strategy for valueless parameters. Even the void can speak volumes.

Walking the path of external libraries

External libraries like Guava or Spring's UriComponentsBuilder bring elegant parsing moves with lesser effort:

// With Guava's Splitter
Map<String, String> query_pairs = Splitter.on('&')
        .trimResults()
        .withKeyValueSeparator('=')
        .split(uri.getQuery());

// With Spring's UriComponentsBuilder
MultiValueMap<String, String> params = UriComponentsBuilder.fromUriString(uri.toString())
        .build()
        .getQueryParams();
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USPs:

• Easy syntax and high-performance.
• Handles multiple value pairs and automatic encoding quirks. Yes! There's no more tears for encodings.

Polishing parsing strategies

Custom parsing or pre-built library?

While falling between a custom method and an external library, remember:

• Reliability: Libraries have been bullied by more bugs than your custom method.
• Performance: Libraries might surf through complex strings better.
• Maintenance: Libraries keep quiet and handle edge cases, as well as updates.

Robustness testing

Test your method with diverse URIs to ensure robustness:

// Add test URIs with varying complexities
String[] testUris = {
    "http://example.com/",
    "http://example.com/?param=value&empty",
    "http://example.com/?param1=value1&&param2=",
};

// Exercise your parsing on each test URI and validate results
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Mastering character encoding

Correct character encoding can prevent a promising Sunday turning into a debugging marathon:

URLEncodedUtils.parse(uri, Charset.forName("UTF-8"));
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Remember:

• UTF-8 is the fairy godmother of the web.
• Java's StandardCharsets comes with the necessary character sets.