Lab 14: Text Blocks & String Processing

Objective

Master Java 21 text blocks for multiline strings, String.formatted(), stripIndent(), translateEscapes(), and advanced string processing: String.format with locale, String.join/Collectors.joining, StringBuilder tricks, regex with named groups, and a template engine using text blocks.

Background

Text blocks (JEP 378, Java 15+) are multiline string literals delimited by """. The compiler automatically strips common leading whitespace (stripIndent()). This enables embedding JSON, HTML, SQL, and YAML directly in code without escaping or concatenation — a major readability improvement.

Time

25 minutes

Prerequisites

Practitioner Lab 07 (Java 21 Features)

Tools

Docker: zchencow/innozverse-java:latest

Lab Instructions

Steps 1–8: Text block basics, stripIndent, HTML templates, JSON, SQL, formatted(), regex named groups, Capstone invoice generator

cat > /tmp/AdvLab14.java << 'JAVAEOF'
import java.util.*;
import java.util.regex.*;
import java.util.stream.*;

public class AdvLab14 {
    record Product(int id, String name, String category, double price, int qty) {}

    // Text block template engine
    static String renderHtml(List<Product> products) {
        var rows = products.stream()
            .map(p -> "    <tr><td>%d</td><td>%s</td><td>$%.2f</td><td>%d</td><td>$%.2f</td></tr>"
                .formatted(p.id(), p.name(), p.price(), p.qty(), p.price()*p.qty()))
            .collect(Collectors.joining("\n"));
        double total = products.stream().mapToDouble(p -> p.price()*p.qty()).sum();
        return """
                <!DOCTYPE html>
                <html>
                <head><title>innoZverse Invoice</title></head>
                <body>
                  <h1>Order Invoice</h1>
                  <table border="1">
                    <tr><th>ID</th><th>Product</th><th>Price</th><th>Qty</th><th>Subtotal</th></tr>
                %s
                    <tr><td colspan="4"><b>TOTAL</b></td><td><b>$%.2f</b></td></tr>
                  </table>
                </body>
                </html>
                """.formatted(rows, total);
    }

    static String renderJson(List<Product> products) {
        var items = products.stream()
            .map(p -> """
                    {"id":%d,"name":"%s","price":%.2f,"qty":%d}""".formatted(
                    p.id(), p.name(), p.price(), p.qty()))
            .collect(Collectors.joining(",\n"));
        double total = products.stream().mapToDouble(p -> p.price()*p.qty()).sum();
        return """
                {
                  "invoice": {
                    "items": [
                %s
                    ],
                    "total": %.2f
                  }
                }
                """.formatted(items, total);
    }

    public static void main(String[] args) {
        var products = List.of(
            new Product(1,"Surface Pro","Laptop",864.0,2),
            new Product(2,"Surface Pen","Accessory",49.99,3),
            new Product(3,"Office 365","Software",99.99,1));

        // Step 1: Text block basics
        System.out.println("=== Text Block Basics ===");
        String sql = """
                SELECT p.name, SUM(o.qty) as units, SUM(o.total) as revenue
                FROM products p
                JOIN orders o ON p.id = o.product_id
                WHERE o.created_at > date('now', '-30 days')
                GROUP BY p.id
                ORDER BY revenue DESC
                LIMIT 10;
                """;
        System.out.println("SQL query (" + sql.lines().count() + " lines):");
        sql.lines().forEach(l -> System.out.println("  " + l));

        // Step 2: stripIndent() and translateEscapes()
        System.out.println("=== stripIndent / translateEscapes ===");
        String raw = "  line 1\n  line 2\n  line 3\n";
        System.out.println("stripped:\n" + raw.stripIndent());
        String escaped = "Tab:\\t  Newline:\\n  Quote:\\\"";
        System.out.println("translated: " + escaped.translateEscapes());

        // Step 3: String.formatted vs String.format
        System.out.println("=== String.formatted ===");
        products.forEach(p ->
            System.out.println("  " + "%-15s @ $%8.2f x%d = $%,.2f"
                .formatted(p.name(), p.price(), p.qty(), p.price()*p.qty())));
        double total = products.stream().mapToDouble(p->p.price()*p.qty()).sum();
        System.out.println("  " + "%-15s   %8s         $%,.2f".formatted("TOTAL", "", total));

        // Step 4: Collectors.joining
        System.out.println("\n=== Collectors.joining ===");
        String names = products.stream().map(Product::name)
            .collect(Collectors.joining(", ", "[", "]"));
        System.out.println("  Names: " + names);

        String csv = products.stream()
            .map(p -> "%d,%s,%.2f,%d".formatted(p.id(),p.name(),p.price(),p.qty()))
            .collect(Collectors.joining("\n", "id,name,price,qty\n", ""));
        System.out.println("  CSV:\n" + csv.indent(4).stripTrailing());

        // Step 5: HTML rendering
        System.out.println("\n=== HTML Template ===");
        String html = renderHtml(products);
        html.lines().limit(8).forEach(l -> System.out.println("  " + l));
        System.out.println("  ... (" + html.lines().count() + " lines total)");

        // Step 6: JSON rendering
        System.out.println("\n=== JSON Template ===");
        String json = renderJson(products);
        json.lines().forEach(l -> System.out.println("  " + l));

        // Step 7: Regex with named groups
        System.out.println("=== Regex Named Groups ===");
        var orderPattern = Pattern.compile(
            "Order #(?<id>\\d+): (?<product>.+?) qty=(?<qty>\\d+) @\\$(?<price>[\\d.]+)");
        var testOrders = List.of(
            "Order #1001: Surface Pro qty=2 @$864.00",
            "Order #1002: Surface Pen qty=5 @$49.99",
            "Order #1003: USB-C Hub qty=1 @$29.99");
        double orderTotal = 0;
        for (var line : testOrders) {
            var m = orderPattern.matcher(line);
            if (m.matches()) {
                double lineTotal = Double.parseDouble(m.group("price")) * Integer.parseInt(m.group("qty"));
                orderTotal += lineTotal;
                System.out.printf("  #%-6s %-15s qty=%s  $%.2f%n",
                    m.group("id"), m.group("product"), m.group("qty"), lineTotal);
            }
        }
        System.out.printf("  Order total: $%,.2f%n", orderTotal);

        // Step 8: StringBuilder for high-throughput
        System.out.println("\n=== StringBuilder Report ===");
        var sb = new StringBuilder();
        sb.append("=== innoZverse Sales Report ===\n");
        products.forEach(p -> sb.append("  %-15s  $%.2f x %d%n".formatted(p.name(), p.price(), p.qty())));
        sb.append("  %-15s  $%,.2f%n".formatted("Grand Total", total));
        System.out.print(sb);
    }
}
JAVAEOF
docker run --rm -v /tmp/AdvLab14.java:/tmp/AdvLab14.java zchencow/innozverse-java:latest sh -c "javac /tmp/AdvLab14.java -d /tmp && java -cp /tmp AdvLab14"

💡 Text blocks use """...""" and automatically strip leading whitespace. The JVM computes the "incidental whitespace" from the least-indented line and strips it uniformly. This means you can indent the content for readability without it appearing in the output. The closing """ on its own line controls this baseline — move it left to keep more indentation.

📸 Verified Output:

=== Text Block Basics ===
SQL query (7 lines):
  SELECT p.name, SUM(o.qty) as units, SUM(o.total) as revenue
  FROM products p
  ...

=== String.formatted ===
  Surface Pro     @  $ 864.00 x2 = $1,728.00
  Surface Pen     @  $  49.99 x3 = $149.97
  Office 365      @  $  99.99 x1 = $99.99
  TOTAL                           $1,977.96

=== JSON Template ===
  {
    "invoice": {
      "items": [
          {"id":1,"name":"Surface Pro","price":864.00,"qty":2},
          ...
      ],
      "total": 1977.96
    }
  }

=== Regex Named Groups ===
  #1001   Surface Pro     qty=2  $1,728.00
  #1002   Surface Pen     qty=5  $249.95
  #1003   USB-C Hub       qty=1  $29.99
  Order total: $2,007.94

Summary

Feature

Syntax

Notes

Text block

"""..."""

Strips leading whitespace

Interpolation

str.formatted(args)

Like String.format on instance

stripIndent()

.stripIndent()

Manual strip incidental WS

Named group

(?<name>...) + .group("name")

Readable regex

Joining

Collectors.joining(sep, pre, suf)

Stream → delimited string

Good afternoon

Lab 14: Text Blocks & String Processing

Objective

Background

Time

Prerequisites

Tools

Lab Instructions

Steps 1–8: Text block basics, stripIndent, HTML templates, JSON, SQL, formatted(), regex named groups, Capstone invoice generator

Summary

Further Reading

Good afternoon

hashtagObjective

hashtagBackground

hashtagTime

hashtagPrerequisites

hashtagTools

hashtagLab Instructions

hashtagSteps 1–8: Text block basics, stripIndent, HTML templates, JSON, SQL, formatted(), regex named groups, Capstone invoice generator

hashtagSummary

hashtagFurther Reading

Objective

Background

Time

Prerequisites

Tools

Lab Instructions

Steps 1–8: Text block basics, stripIndent, HTML templates, JSON, SQL, formatted(), regex named groups, Capstone invoice generator

Summary

Further Reading