Add a text banner formatter

src/main/java/org/jboss/logmanager/ExtFormatter.java

@@ -21,6 +21,7 @@
 
 import java.text.MessageFormat;
 import java.util.MissingResourceException;
+import java.util.Objects;
 import java.util.ResourceBundle;
 import java.util.logging.Formatter;
 import java.util.logging.Handler;
@@ -172,4 +173,47 @@ public String getTail(Handler h) {
             return formatter.getTail(h);
         }
     }
+
+    /**
+     * A base class for formatters which wrap other formatters.
+     */
+    public abstract static class Delegating extends ExtFormatter {
+        /**
+         * The delegate formatter.
+         */
+        protected final ExtFormatter delegate;
+
+        /**
+         * Construct a new instance.
+         *
+         * @param delegate the delegate formatter (must not be {@code null})
+         */
+        public Delegating(final ExtFormatter delegate) {
+            this.delegate = Objects.requireNonNull(delegate, "delegate");
+        }
+
+        public String format(final ExtLogRecord record) {
+            return delegate.format(record);
+        }
+
+        public String formatMessage(final LogRecord record) {
+            return delegate.formatMessage(record);
+        }
+
+        public boolean isCallerCalculationRequired() {
+            return delegate.isCallerCalculationRequired();
+        }
+
+        public String format(final LogRecord record) {
+            return delegate.format(record);
+        }
+
+        public String getHead(final Handler h) {
+            return delegate.getHead(h);
+        }
+
+        public String getTail(final Handler h) {
+            return delegate.getTail(h);
+        }
+    }
 }

src/main/java/org/jboss/logmanager/formatters/TextBannerFormatter.java

@@ -0,0 +1,159 @@
+package org.jboss.logmanager.formatters;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
+import java.util.Objects;
+import java.util.function.Supplier;
+import java.util.logging.Handler;
+
+import org.jboss.logmanager.ExtFormatter;
+
+/**
+ * A formatter which prints a text banner ahead of the normal formatter header.
+ * The text banner is acquired from a {@link Supplier} which is passed in to the constructor.
+ * Several utility methods are also present which allow easy creation of {@code Supplier} instances.
+ */
+public final class TextBannerFormatter extends ExtFormatter.Delegating {
+    private final Supplier<String> bannerSupplier;
+
+    /**
+     * Construct a new instance.
+     *
+     * @param bannerSupplier the supplier for the banner (must not be {@code null})
+     * @param delegate the delegate formatter (must not be {@code null})
+     */
+    public TextBannerFormatter(final Supplier<String> bannerSupplier, final ExtFormatter delegate) {
+        super(delegate);
+        this.bannerSupplier = Objects.requireNonNull(bannerSupplier, "bannerSupplier");
+    }
+
+    // doc inherited
+    public String getHead(final Handler h) {
+        final String dh = Objects.requireNonNullElse(delegate.getHead(h), "");
+        final String banner = Objects.requireNonNullElse(bannerSupplier.get(), "");
+        return banner + dh;
+    }
+
+    /**
+     * Get the empty supplier which always returns an empty string.
+     *
+     * @return the empty supplier (not {@code null})
+     */
+    public static Supplier<String> getEmptySupplier() {
+        return EMPTY;
+    }
+
+    /**
+     * Create a supplier which always returns the given string.
+     *
+     * @param string the string (must not be {@code null})
+     * @return a supplier which returns the given string (not {@code null})
+     */
+    public static Supplier<String> createStringSupplier(String string) {
+        Objects.requireNonNull(string, "string");
+        return () -> string;
+    }
+
+    /**
+     * Create a supplier which loads the banner from the given file path,
+     * falling back to the given fallback supplier on error.
+     *
+     * @param path the path to load from (must not be {@code null})
+     * @param fallback the fallback supplier (must not be {@code null})
+     * @return the supplier (not {@code null})
+     */
+    public static Supplier<String> createFileSupplier(Path path, Supplier<String> fallback) {
+        Objects.requireNonNull(path, "path");
+        Objects.requireNonNull(fallback, "fallback");
+        return () -> {
+            try {
+                return Files.readString(path, StandardCharsets.UTF_8);
+            } catch (IOException ignored) {
+                return fallback.get();
+            }
+        };
+    }
+
+    /**
+     * Create a supplier which loads the banner from the given URL,
+     * falling back to the given fallback supplier on error.
+     *
+     * @param url the URL to load from (must not be {@code null})
+     * @param fallback the fallback supplier (must not be {@code null})
+     * @return the supplier (not {@code null})
+     */
+    public static Supplier<String> createUrlSupplier(URL url, Supplier<String> fallback) {
+        Objects.requireNonNull(url, "url");
+        Objects.requireNonNull(fallback, "fallback");
+        return () -> {
+            try {
+                final InputStream is = url.openStream();
+                return is == null ? fallback.get() : loadStringFromStream(is);
+            } catch (IOException ignored) {
+                return fallback.get();
+            }
+        };
+    }
+
+    /**
+     * Create a supplier which loads the banner from a resource in the given class loader,
+     * falling back to the given fallback supplier on error.
+     *
+     * @param resource the resource name (must not be {@code null})
+     * @param classLoader the class loader to load from (must not be {@code null})
+     * @param fallback the fallback supplier (must not be {@code null})
+     * @return the supplier (not {@code null})
+     */
+    public static Supplier<String> createResourceSupplier(String resource, ClassLoader classLoader, Supplier<String> fallback) {
+        Objects.requireNonNull(resource, "resource");
+        Objects.requireNonNull(classLoader, "classLoader");
+        Objects.requireNonNull(fallback, "fallback");
+        return () -> {
+            try {
+                final InputStream is = classLoader.getResourceAsStream(resource);
+                return is == null ? fallback.get() : loadStringFromStream(is);
+            } catch (IOException ignored) {
+                return fallback.get();
+            }
+        };
+    }
+
+    /**
+     * Create a supplier which loads the banner from a resource in the caller's class loader,
+     * falling back to the given fallback supplier on error.
+     *
+     * @param resource the resource name (must not be {@code null})
+     * @param fallback the fallback supplier (must not be {@code null})
+     * @return the supplier (not {@code null})
+     */
+    public static Supplier<String> createResourceSupplier(String resource, Supplier<String> fallback) {
+        return createResourceSupplier(resource, getClassLoader(STACK_WALKER.getCallerClass()), fallback);
+    }
+
+    // private stuff
+
+    private static final Supplier<String> EMPTY = createStringSupplier("");
+    private static final StackWalker STACK_WALKER = AccessController.doPrivileged((PrivilegedAction<StackWalker>) () -> StackWalker.getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE));
+
+    private static ClassLoader getClassLoader(Class<?> clazz) {
+        return AccessController.doPrivileged((PrivilegedAction<? extends ClassLoader>) clazz::getClassLoader);
+    }
+
+    private static String loadStringFromStream(final InputStream is) throws IOException {
+        try (is) {
+            try (InputStreamReader isr = new InputStreamReader(is, StandardCharsets.UTF_8)) {
+                try (StringBuilderWriter sw = new StringBuilderWriter()) {
+                    isr.transferTo(sw);
+                    return sw.toString();
+                }
+            }
+        }
+    }
+}