Kódování Base64 v Javě — Příklady java.util.Base64

import java.util.Base64;
import java.nio.charset.StandardCharsets;

public class EncodeDemo {
    public static void main(String[] args) {
        String credentials = "monitoring-svc:9f2a7c4e-b1d8-4a3f";
        byte[] credentialBytes = credentials.getBytes(StandardCharsets.UTF_8);

        String encoded = Base64.getEncoder().encodeToString(credentialBytes);
        System.out.println(encoded);
        // bW9uaXRvcmluZy1zdmM6OWYyYTdjNGUtYjFkOC00YTNm
    }
}

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.Base64;
import java.nio.charset.StandardCharsets;

public class BasicAuthExample {
    public static void main(String[] args) throws Exception {
        String username = "metrics-exporter";
        String apiKey = "sk_live_4eC39HqLyjWDarjtT1zdp7dc";

        // username:password → Base64
        String credentials = username + ":" + apiKey;
        String authHeader = "Basic " + Base64.getEncoder()
            .encodeToString(credentials.getBytes(StandardCharsets.UTF_8));

        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("https://api.example.com/v2/metrics"))
            .header("Authorization", authHeader)
            .build();

        HttpResponse<String> response = HttpClient.newHttpClient()
            .send(request, HttpResponse.BodyHandlers.ofString());

        System.out.println(response.statusCode());  // 200
    }
}

import java.util.Base64;
import java.nio.charset.StandardCharsets;

public class RoundTrip {
    public static void main(String[] args) {
        String original = "X-Correlation-ID: req_8a4f2c91-e7b3-4d56-9012-3f7a8b9c0d1e";

        // Kódování
        String encoded = Base64.getEncoder()
            .encodeToString(original.getBytes(StandardCharsets.UTF_8));
        System.out.println(encoded);
        // WC1Db3JyZWxhdGlvbi1JRDogcmVxXzhhNGYyYzkxLWU3YjMtNGQ1Ni05MDEyLTNmN2E4YjljMGQxZQ==

        // Dekódování
        byte[] decodedBytes = Base64.getDecoder().decode(encoded);
        String decoded = new String(decodedBytes, StandardCharsets.UTF_8);

        System.out.println(original.equals(decoded));  // true
    }
}

import java.util.Base64;
import java.util.UUID;
import java.nio.charset.StandardCharsets;

UUID sessionId = UUID.fromString("6ba7b810-9dad-11d1-80b4-00c04fd430c8");
String encoded = Base64.getEncoder()
    .encodeToString(sessionId.toString().getBytes(StandardCharsets.UTF_8));
System.out.println(encoded);
// NmJhN2I4MTAtOWRhZC0xMWQxLTgwYjQtMDBjMDRmZDQzMGM4

import java.nio.ByteBuffer;
import java.util.Base64;
import java.util.UUID;

UUID eventId = UUID.fromString("550e8400-e29b-41d4-a716-446655440000");

ByteBuffer buffer = ByteBuffer.wrap(new byte[16]);
buffer.putLong(eventId.getMostSignificantBits());
buffer.putLong(eventId.getLeastSignificantBits());

String compact = Base64.getUrlEncoder()
    .withoutPadding()
    .encodeToString(buffer.array());
System.out.println(compact);
// VQ6EAOKbQdSnFkRmVUQAAA
// 22 znaků oproti 48 u přístupu přes řetězec

import java.time.Instant;
import java.util.Base64;
import java.nio.charset.StandardCharsets;

// Simulace JWT-style payloadu
String payload = String.format(
    "{"sub":"usr_7b3c","iss":"auth.internal","iat":%d,"exp":%d}",
    Instant.now().getEpochSecond(),
    Instant.now().plusSeconds(3600).getEpochSecond()
);

String encoded = Base64.getUrlEncoder()
    .withoutPadding()
    .encodeToString(payload.getBytes(StandardCharsets.UTF_8));
System.out.println(encoded);
// eyJzdWIiOiJ1c3JfN2IzYyIsImlzcyI6ImF1dGguaW50ZXJuYWwiLCJpYXQiOj... (URL-bezpečné, bez paddingu)

import java.util.Base64;
import java.nio.charset.StandardCharsets;

String redirectUri = "https://app.internal/callback?state=auth_pending&nonce=9f2a7c";
byte[] data = redirectUri.getBytes(StandardCharsets.UTF_8);

// Standardní kodér — obsahuje + a / které narušují URL
String standard = Base64.getEncoder().encodeToString(data);
System.out.println(standard);
// aHR0cHM6Ly9hcHAuaW50ZXJuYWwvY2FsbGJhY2s/c3RhdGU9YXV0aF9wZW5kaW5nJm5vbmNlPTlmMmE3Yw==

// URL-bezpečný kodér — bezpečný pro parametry dotazů a názvy souborů
String urlSafe = Base64.getUrlEncoder().encodeToString(data);
System.out.println(urlSafe);
// aHR0cHM6Ly9hcHAuaW50ZXJuYWwvY2FsbGJhY2s_c3RhdGU9YXV0aF9wZW5kaW5nJm5vbmNlPTlmMmE3Yw==

// URL-bezpečný bez paddingu — pro JWT a kompaktní tokeny
String noPadding = Base64.getUrlEncoder().withoutPadding().encodeToString(data);
System.out.println(noPadding);
// aHR0cHM6Ly9hcHAuaW50ZXJuYWwvY2FsbGJhY2s_c3RhdGU9YXV0aF9wZW5kaW5nJm5vbmNlPTlmMmE3Yw

import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Base64;

public class FileEncoder {
    public static void main(String[] args) {
        try {
            byte[] fileBytes = Files.readAllBytes(Path.of("certs/server.pem"));
            String encoded = Base64.getEncoder().encodeToString(fileBytes);

            System.out.printf("Původní: %d bajtů%n", fileBytes.length);
            System.out.printf("Zakódováno: %d znaků%n", encoded.length());

            // Zápis zakódovaného obsahu do textového souboru
            Files.writeString(
                Path.of("certs/server.pem.b64"),
                encoded
            );
        } catch (java.io.IOException e) {
            System.err.println("Nepodařilo se načíst soubor: " + e.getMessage());
        }
    }
}

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.Base64;

public class ApiEncoder {
    public static void main(String[] args) {
        try {
            HttpClient client = HttpClient.newHttpClient();
            HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("https://api.example.com/v2/reports/weekly.pdf"))
                .header("Authorization", "Bearer tok_8f2a9c3d")
                .build();

            HttpResponse<byte[]> response = client.send(
                request, HttpResponse.BodyHandlers.ofByteArray()
            );

            if (response.statusCode() == 200) {
                String encoded = Base64.getEncoder()
                    .encodeToString(response.body());
                System.out.printf("Zakódováno %d bajtů → %d znaků%n",
                    response.body().length, encoded.length());
            } else {
                System.err.printf("HTTP %d: %s%n",
                    response.statusCode(),
                    new String(response.body()));
            }
        } catch (Exception e) {
            System.err.println("Požadavek selhal: " + e.getMessage());
        }
    }
}

# macOS / Linux — zakódování řetězce
echo -n "deploy-bot:sk_prod_9f2a7c4e" | base64
# ZGVwbG95LWJvdDpza19wcm9kXzlmMmE3YzRl

# Zakódování souboru
base64 < certs/server.pem > certs/server.pem.b64

# Pomocí jshell (JDK 9+)
echo 'System.out.println(java.util.Base64.getEncoder().encodeToString("deploy-bot:sk_prod_9f2a7c4e".getBytes()))' | jshell -

# Pomocí java přímo jako jednořádkový příkaz
java -e 'System.out.println(java.util.Base64.getEncoder().encodeToString(args[0].getBytes()))' "my-secret"
# Poznámka: java -e vyžaduje JDK 23+ (JEP 477)

// Maven: org.apache.commons:commons-codec:1.17.0
import org.apache.commons.codec.binary.Base64;
import java.nio.charset.StandardCharsets;

byte[] telemetryPayload = ("{"service":"metrics-collector","
    + ""host":"prod-east-07","
    + ""cpu_pct":72.4,"
    + ""mem_mb":3891,"
    + ""timestamp":1710523200}")
    .getBytes(StandardCharsets.UTF_8);

// Standardní kódování
String encoded = Base64.encodeBase64String(telemetryPayload);

// URL-bezpečné kódování
String urlSafe = Base64.encodeBase64URLSafeString(telemetryPayload);

// Ověření, zda je řetězec platné Base64
boolean valid = Base64.isBase64(encoded);
System.out.println(valid);  // true

// Maven: com.google.guava:guava:33.1.0-jre
import com.google.common.io.BaseEncoding;
import java.nio.charset.StandardCharsets;

byte[] webhookPayload = ("{"event":"deployment.completed","
    + ""repo":"payments-api","
    + ""sha":"a7f2c91e4b3d","
    + ""environment":"production"}")
    .getBytes(StandardCharsets.UTF_8);

// Standardní Base64
String standard = BaseEncoding.base64().encode(webhookPayload);

// URL-bezpečné
String urlSafe = BaseEncoding.base64Url().encode(webhookPayload);

// Bez paddingu
String noPad = BaseEncoding.base64Url().omitPadding().encode(webhookPayload);

// Se zalomením řádků (PEM styl)
String wrapped = BaseEncoding.base64()
    .withSeparator("\n", 64)
    .encode(webhookPayload);

import java.util.Base64;
import java.nio.charset.StandardCharsets;

// Simulace těla PEM certifikátu
byte[] certData = new byte[256];  // V praxi načtěte z .der souboru
new java.security.SecureRandom().nextBytes(certData);

// Výchozí MIME kodér — 76 znaků na řádek, oddělovač \r\n
String mimeEncoded = Base64.getMimeEncoder().encodeToString(certData);
System.out.println(mimeEncoded);
// QYx2K3p8Xg7JmN1R+wFkLd...  (76 znaků)
// Ht5Bv9CzAq0PnSjYl8WxUe...  (76 znaků)
// ...

// Vlastní MIME kodér — 64 znaků na řádek (standard PEM), oddělovač \n
Base64.Encoder pemEncoder = Base64.getMimeEncoder(64, new byte[]{'\n'});
String pemBody = pemEncoder.encodeToString(certData);
System.out.println("-----BEGIN CERTIFICATE-----");
System.out.println(pemBody);
System.out.println("-----END CERTIFICATE-----");

import java.io.*;
import java.nio.file.*;
import java.util.Base64;

public class StreamingEncoder {
    public static void main(String[] args) throws IOException {
        Path inputPath = Path.of("backups/database-export.sql.gz");
        Path outputPath = Path.of("backups/database-export.sql.gz.b64");

        try (
            InputStream in = Files.newInputStream(inputPath);
            OutputStream fileOut = Files.newOutputStream(outputPath);
            OutputStream base64Out = Base64.getEncoder().wrap(fileOut)
        ) {
            byte[] buffer = new byte[8192];
            int bytesRead;
            long totalBytes = 0;

            while ((bytesRead = in.read(buffer)) != -1) {
                base64Out.write(buffer, 0, bytesRead);
                totalBytes += bytesRead;
            }

            System.out.printf("Streamováno %d bajtů přes Base64 kodér%n", totalBytes);
        }
        // Uzavření base64Out automaticky zapíše poslední padding bajty
    }
}

import java.io.ByteArrayOutputStream;
import java.io.OutputStream;
import java.util.Base64;
import java.nio.charset.StandardCharsets;

ByteArrayOutputStream buffer = new ByteArrayOutputStream();

try (OutputStream encoder = Base64.getEncoder().wrap(buffer)) {
    // Zápis dat po částech — simuluje čtení ze streamu
    encoder.write("chunk-1:telemetry-data-".getBytes(StandardCharsets.UTF_8));
    encoder.write("chunk-2:more-payload-".getBytes(StandardCharsets.UTF_8));
    encoder.write("chunk-3:final-segment".getBytes(StandardCharsets.UTF_8));
}

String encoded = buffer.toString(StandardCharsets.UTF_8);
System.out.println(encoded);
// Y2h1bmstMTp0ZWxlbWV0cnktZGF0YS1jaHVuay0yOm1vcmUtcGF5bG9hZC1jaHVuay0zOmZpbmFsLXNlZ21lbnQ=

// Ověření zpětné konverze
byte[] decoded = Base64.getDecoder().decode(encoded);
System.out.println(new String(decoded, StandardCharsets.UTF_8));
// chunk-1:telemetry-data-chunk-2:more-payload-chunk-3:final-segment

import java.util.Base64;
import java.nio.charset.StandardCharsets;

public class TokenService {
    // Vytvoří se jednou, používá se všude — thread-safe
    private static final Base64.Encoder STANDARD = Base64.getEncoder();
    private static final Base64.Encoder URL_SAFE = Base64.getUrlEncoder().withoutPadding();
    private static final Base64.Encoder MIME = Base64.getMimeEncoder();

    public static String encodeForHeader(String value) {
        return STANDARD.encodeToString(value.getBytes(StandardCharsets.UTF_8));
    }

    public static String encodeForUrl(byte[] data) {
        return URL_SAFE.encodeToString(data);
    }

    public static String encodeForEmail(byte[] attachment) {
        return MIME.encodeToString(attachment);
    }
}