Add LogOutputStream.create(LineConsumer) (#107)

So instead of creating an anonymous class it can be one-liner with a lambda expression.

README.md

@@ -160,7 +160,17 @@ new ProcessExecutor().command("java", "-version")
 
 <hr/>
 
-* Handling output line-by-line while process is running
+* Handling output line-by-line while process is running (Java 8+)
+
+```java
+new ProcessExecutor().command("java", "-version")
+    .redirectOutput(line -> ...)
+    .execute();
+```
+
+<hr/>
+
+* Handling output line-by-line while process is running (prior to Java 8)
 
 ```java
 new ProcessExecutor().command("java", "-version")
@@ -264,4 +274,3 @@ Future<ProcessResult> future = new ProcessExecutor()
 // do some stuff
 String output = future.get(60, TimeUnit.SECONDS).outputUTF8();
 ```
-

src/main/java/org/zeroturnaround/exec/ProcessExecutor.java

@@ -136,8 +136,8 @@ public class ProcessExecutor {
     // Run in case of any constructor
     exitValues(DEFAULT_EXIT_VALUES);
     stopper(DestroyProcessStopper.INSTANCE);
-    redirectOutput(null);
-    redirectError(null);
+    redirectOutput(NullOutputStream.NULL_OUTPUT_STREAM);
+    redirectError(NullOutputStream.NULL_OUTPUT_STREAM);
     destroyer(null);
     redirectErrorStream(DEFAULT_REDIRECT_ERROR_STREAM);
   }
@@ -471,6 +471,19 @@ public ProcessExecutor redirectOutput(OutputStream output) {
     return streams(new PumpStreamHandler(output, pumps == null ? null : pumps.getErr(), pumps == null ? null : pumps.getInput()));
   }
 
+  /**
+   * Redirects the process' output stream to given line consumer.
+   * If this method is invoked multiple times each call overwrites the previous.
+   * Use {@link #redirectOutputAlsoTo(OutputStream)} if you want to redirect the output to multiple streams.
+   *
+   * @param consumer consumer where the process output is redirected to.
+   * @return This process executor.
+   * @see #redirectOutput(OutputStream)
+   */
+  public ProcessExecutor redirectOutput(LineConsumer consumer) {
+    return redirectOutput(LogOutputStream.create(consumer));
+  }
+
   /**
    * Redirects the process' error stream to given output stream.
    * If this method is invoked multiple times each call overwrites the previous.
@@ -492,6 +505,19 @@ public ProcessExecutor redirectError(OutputStream output) {
     return this;
   }
 
+  /**
+   * Redirects the process' error stream to given line consumer.
+   * If this method is invoked multiple times each call overwrites the previous.
+   * Use {@link #redirectErrorAlsoTo(OutputStream)} if you want to redirect the output to multiple streams.
+   *
+   * @param consumer consumer where the process error is redirected to.
+   * @return This process executor.
+   * @see #redirectError(OutputStream)
+   */
+  public ProcessExecutor redirectError(LineConsumer consumer) {
+    return redirectError(LogOutputStream.create(consumer));
+  }
+
   /**
    * Redirects the process' output stream also to a given output stream.
    * This method can be used to redirect output to multiple streams.

src/main/java/org/zeroturnaround/exec/stream/LineConsumer.java

@@ -0,0 +1,9 @@
+package org.zeroturnaround.exec.stream;
+
+/**
+ * This is equivalent to {@code java.util.function.Consumer} while staying compatible with
+ * Java versions earlier than 8.
+ */
+public interface LineConsumer {
+  void accept(String line);
+}

src/main/java/org/zeroturnaround/exec/stream/LogOutputStream.java

@@ -21,7 +21,6 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.UnsupportedEncodingException;
-import java.nio.charset.Charset;
 
 /**
  * Base class to connect a logging system to the output and/or
@@ -32,7 +31,7 @@
 public abstract class LogOutputStream extends OutputStream {
 
   /** Initial buffer size. */
-  private static final int INTIAL_SIZE = 132;
+  private static final int INITIAL_SIZE = 132;
 
   /** Carriage return */
   private static final int CR = 0x0d;
@@ -42,7 +41,7 @@ public abstract class LogOutputStream extends OutputStream {
 
   /** the internal buffer */
   private final ByteArrayOutputStream buffer = new ByteArrayOutputStream(
-      INTIAL_SIZE);
+      INITIAL_SIZE);
 
   byte lastReceivedByte;
 
@@ -159,4 +158,22 @@ protected void processBuffer() {
    */
   protected abstract void processLine(String line);
 
+  /**
+   * Factory method to create a <code>LogOutputStream</code> that passes each line to the specified consumer.
+   * <p>Mostly useful with Java 8+, so the consumer can be passed as a lambda expression.</p>
+   *
+   * @param consumer the consumer to consume the log lines
+   * @return the created <code>LogOutputStream</code>, passing each line to the specified consumer.
+   */
+  public static LogOutputStream create(final LineConsumer consumer) {
+    if (consumer == null) {
+      throw new IllegalArgumentException("Line consumer must be provided.");
+    }
+    return new LogOutputStream() {
+      @Override
+      protected void processLine(String line) {
+        consumer.accept(line);
+      }
+    };
+  }
 }

src/test/java/org/zeroturnaround/exec/test/LogOutputStreamTest.java

@@ -8,6 +8,7 @@
 
 import org.junit.Assert;
 import org.junit.Test;
+import org.zeroturnaround.exec.stream.LineConsumer;
 import org.zeroturnaround.exec.stream.LogOutputStream;
 
 public class LogOutputStreamTest {
@@ -74,4 +75,16 @@ public void testNewLineAtTheEnd() throws UnsupportedEncodingException, IOExcepti
 		testLogOutputStream("foo\n", "foo");
 	}
 
+	@Test
+	public void lambda() throws IOException {
+		final List<String> lines = new ArrayList<String>();
+		LogOutputStream out = LogOutputStream.create(new LineConsumer() {
+			@Override
+			public void accept(String line) {
+				lines.add(line);
+			}
+		});
+		out.write("foo\nbar\n".getBytes());
+		Assert.assertEquals(Arrays.asList("foo", "bar"), lines);
+	}
 }