Introduce LogAccessor and LogMessage as convenient logging utilities

Closes gh-22726

spring-core/src/main/java/org/springframework/core/log/LogAccessor.java

@@ -0,0 +1,280 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.log;
+
+import java.util.function.Supplier;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+/**
+ * A convenient accessor for Commons Logging, providing not only
+ * {@code CharSequence} based log methods but also {@code Supplier}
+ * based variants for use with Java 8 lambda expressions.
+ *
+ * @author Juergen Hoeller
+ * @since 5.2
+ */
+public class LogAccessor {
+
+	private final Log log;
+
+
+	/**
+	 * Create a new accessor for the given Commons Log.
+	 * @see LogFactory#getLog(Class)
+	 * @see LogFactory#getLog(String)
+	 */
+	public LogAccessor(Log log) {
+		this.log = log;
+	}
+
+	/**
+	 * Create a new accessor for the specified Commons Log category.
+	 * @see LogFactory#getLog(Class)
+	 */
+	public LogAccessor(Class<?> logCategory) {
+		this.log = LogFactory.getLog(logCategory);
+	}
+
+	/**
+	 * Create a new accessor for the specified Commons Log category.
+	 * @see LogFactory#getLog(String)
+	 */
+	public LogAccessor(String logCategory) {
+		this.log = LogFactory.getLog(logCategory);
+	}
+
+
+	/**
+	 * Return the target Commons Log.
+	 */
+	public final Log getLog() {
+		return this.log;
+	}
+
+
+	// Plain log methods
+
+	/**
+	 * Log a message with fatal log level.
+	 * @param message the message to log
+	 */
+	public void fatal(CharSequence message) {
+		this.log.fatal(message);
+	}
+
+	/**
+	 * Log an error with fatal log level.
+	 * @param message the message to log
+	 * @param t log this cause
+	 */
+	public void fatal(CharSequence message, Throwable t) {
+		this.log.fatal(message, t);
+	}
+
+	/**
+	 * Log a message with error log level.
+	 * @param message the message to log
+	 */
+	public void error(CharSequence message) {
+		this.log.error(message);
+	}
+
+	/**
+	 * Log an error with error log level.
+	 * @param message the message to log
+	 * @param t log this cause
+	 */
+	public void error(CharSequence message, Throwable t) {
+		this.log.error(message, t);
+	}
+
+	/**
+	 * Log a message with warn log level.
+	 * @param message the message to log
+	 */
+	public void warn(CharSequence message) {
+		this.log.warn(message);
+	}
+
+	/**
+	 * Log an error with warn log level.
+	 * @param message the message to log
+	 * @param t log this cause
+	 */
+	public void warn(CharSequence message, Throwable t) {
+		this.log.warn(message, t);
+	}
+
+	/**
+	 * Log a message with info log level.
+	 * @param message the message to log
+	 */
+	public void info(CharSequence message) {
+		this.log.info(message);
+	}
+
+	/**
+	 * Log an error with info log level.
+	 * @param message the message to log
+	 * @param t log this cause
+	 */
+	public void info(CharSequence message, Throwable t) {
+		this.log.info(message, t);
+	}
+
+	/**
+	 * Log a message with debug log level.
+	 * @param message the message to log
+	 */
+	public void debug(CharSequence message) {
+		this.log.debug(message);
+	}
+
+	/**
+	 * Log an error with debug log level.
+	 * @param message the message to log
+	 * @param t log this cause
+	 */
+	public void debug(CharSequence message, Throwable t) {
+		this.log.debug(message, t);
+	}
+
+	/**
+	 * Log a message with trace log level.
+	 * @param message the message to log
+	 */
+	public void trace(CharSequence message) {
+		this.log.trace(message);
+	}
+
+	/**
+	 * Log an error with trace log level.
+	 * @param message the message to log
+	 * @param t log this cause
+	 */
+	public void trace(CharSequence message, Throwable t) {
+		this.log.trace(message, t);
+	}
+
+
+	// Supplier-based log methods
+
+	/**
+	 * Log a message with fatal log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 */
+	public void fatal(Supplier<? extends CharSequence> messageSupplier) {
+		this.log.fatal(new LogMessage(messageSupplier));
+	}
+
+	/**
+	 * Log an error with fatal log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 * @param t log this cause
+	 */
+	public void fatal(Supplier<? extends CharSequence> messageSupplier, Throwable t) {
+		this.log.fatal(new LogMessage(messageSupplier), t);
+	}
+
+	/**
+	 * Log a message with error log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 */
+	public void error(Supplier<? extends CharSequence> messageSupplier) {
+		this.log.error(new LogMessage(messageSupplier));
+	}
+
+	/**
+	 * Log an error with error log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 * @param t log this cause
+	 */
+	public void error(Supplier<? extends CharSequence> messageSupplier, Throwable t) {
+		this.log.error(new LogMessage(messageSupplier), t);
+	}
+
+	/**
+	 * Log a message with warn log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 */
+	public void warn(Supplier<? extends CharSequence> messageSupplier) {
+		this.log.warn(new LogMessage(messageSupplier));
+	}
+
+	/**
+	 * Log an error with warn log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 * @param t log this cause
+	 */
+	public void warn(Supplier<? extends CharSequence> messageSupplier, Throwable t) {
+		this.log.warn(new LogMessage(messageSupplier), t);
+	}
+
+	/**
+	 * Log a message with info log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 */
+	public void info(Supplier<? extends CharSequence> messageSupplier) {
+		this.log.info(new LogMessage(messageSupplier));
+	}
+
+	/**
+	 * Log an error with info log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 * @param t log this cause
+	 */
+	public void info(Supplier<? extends CharSequence> messageSupplier, Throwable t) {
+		this.log.info(new LogMessage(messageSupplier), t);
+	}
+
+	/**
+	 * Log a message with debug log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 */
+	public void debug(Supplier<? extends CharSequence> messageSupplier) {
+		this.log.debug(new LogMessage(messageSupplier));
+	}
+
+	/**
+	 * Log an error with debug log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 * @param t log this cause
+	 */
+	public void debug(Supplier<? extends CharSequence> messageSupplier, Throwable t) {
+		this.log.debug(new LogMessage(messageSupplier), t);
+	}
+
+	/**
+	 * Log a message with trace log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 */
+	public void trace(Supplier<? extends CharSequence> messageSupplier) {
+		this.log.trace(new LogMessage(messageSupplier));
+	}
+
+	/**
+	 * Log an error with trace log level.
+	 * @param messageSupplier a lazy supplier for the message to log
+	 * @param t log this cause
+	 */
+	public void trace(Supplier<? extends CharSequence> messageSupplier, Throwable t) {
+		this.log.trace(new LogMessage(messageSupplier), t);
+	}
+
+}

spring-core/src/main/java/org/springframework/core/log/LogMessage.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.log;
+
+import java.util.function.Supplier;
+
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * A simple log message type for use with Commons Logging, allowing
+ * for convenient late resolution of a given {@link Supplier} instance
+ * (typically bound to a Java 8 lambda expression) in {@link #toString()}.
+ *
+ * @author Juergen Hoeller
+ * @since 5.2
+ * @see org.apache.commons.logging.Log#fatal(Object)
+ * @see org.apache.commons.logging.Log#error(Object)
+ * @see org.apache.commons.logging.Log#warn(Object)
+ * @see org.apache.commons.logging.Log#info(Object)
+ * @see org.apache.commons.logging.Log#debug(Object)
+ * @see org.apache.commons.logging.Log#trace(Object)
+ */
+public class LogMessage {
+
+	private final Supplier<? extends CharSequence> supplier;
+
+	@Nullable
+	private String result;
+
+
+	/**
+	 * Construct a new {@code LogMessage} for the given supplier.
+	 * @param supplier the lazily resolving supplier
+	 * (typically bound to a Java 8 lambda expression)
+	 */
+	public LogMessage(Supplier<? extends CharSequence> supplier) {
+		Assert.notNull(supplier, "Supplier must not be null");
+		this.supplier = supplier;
+	}
+
+
+	/**
+	 * This will be called by the logging provider, potentially once
+	 * per log target (therefore locally caching the result here).
+	 */
+	@Override
+	public String toString() {
+		if (this.result == null) {
+			this.result = this.supplier.get().toString();
+		}
+		return this.result;
+	}
+
+}

spring-core/src/test/java/org/springframework/core/log/LogSupportTests.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.log;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+/**
+ * @author Juergen Hoeller
+ * @since 5.2
+ */
+public class LogSupportTests {
+
+	@Test
+	public void testLogMessage() {
+		LogMessage msg = new LogMessage(() -> new StringBuilder("a"));
+		assertEquals("a", msg.toString());
+		assertSame(msg.toString(), msg.toString());
+	}
+
+}