Use stream api instead of while loop to read tail of file

lukashinsch · Mar 29, 2015 · a07dd87 · a07dd87
1 parent d693556
commit a07dd87
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Showing 3 changed files with 31 additions and 8 deletions.
diff --git a/lib/lib.gradle b/lib/lib.gradle
@@ -36,6 +36,7 @@ dependencies {
     compile("org.ocpsoft.prettytime:prettytime:3.2.7.Final")
     compile("commons-io:commons-io:2.4")
     compile("org.apache.commons:commons-compress:1.9")
+    compile("com.codepoetics:protonpack:1.4")
 
     testCompile("org.springframework.boot:spring-boot-starter-test:${springBootVersion}")
 }

diff --git a/lib/src/main/java/eu/hinsch/spring/boot/actuator/logview/FileSystemFileProvider.java b/lib/src/main/java/eu/hinsch/spring/boot/actuator/logview/FileSystemFileProvider.java
@@ -1,5 +1,6 @@
 package eu.hinsch.spring.boot.actuator.logview;
 
+import com.codepoetics.protonpack.StreamUtils;
 import org.apache.commons.io.IOUtils;
 import org.apache.commons.io.input.ReversedLinesFileReader;
 
@@ -11,9 +12,10 @@
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.Date;
+import java.util.LinkedList;
 import java.util.List;
+import java.util.stream.Stream;
 
 /**
 * Created by lh on 28/02/15.
@@ -74,14 +76,20 @@ private File getFile(Path folder, String filename) {
     @Override
     public void tailContent(Path folder, String filename, OutputStream stream, int lines) throws IOException {
         try (ReversedLinesFileReader reader = new ReversedLinesFileReader(getFile(folder, filename))) {
-            int i = 0;
-            String line;
-            List<String> content = new ArrayList<>();
-            while ((line = reader.readLine()) != null && i++ < lines) {
-                content.add(line);
-            }
-            Collections.reverse(content);
+            List<String> content = StreamUtils.takeWhile(
+                        Stream.generate(() -> readLine(reader)),
+                        line -> line != null)
+                    .limit(lines)
+                    .collect(LinkedList::new, LinkedList::addFirst, LinkedList::addAll);
             IOUtils.writeLines(content, System.lineSeparator(), stream);
         }
     }
+
+    private String readLine(ReversedLinesFileReader reader) {
+        try {
+            return reader.readLine();
+        } catch (IOException e) {
+            throw new RuntimeException("cannot read line", e);
+        }
+    }
 }
diff --git a/lib/src/test/java/eu/hinsch/spring/boot/actuator/logview/LogViewEndpointTest.java b/lib/src/test/java/eu/hinsch/spring/boot/actuator/logview/LogViewEndpointTest.java
@@ -362,6 +362,20 @@ public void shouldTailViewOnlyLastLine() throws Exception {
         assertThat(new String(outputStream.toByteArray()), containsString("line2"));
     }
 
+    @Test
+    public void shouldTailHandleMoreRequestedLinesThanExist() throws Exception {
+        // given
+        createFile("file.log", "line1" + System.lineSeparator() + "line2" + System.lineSeparator(), now);
+        ByteArrayServletOutputStream outputStream = mockResponseOutputStream();
+
+        // when
+        logViewEndpoint.view("file.log", null, 3, response);
+
+        // then
+        assertThat(new String(outputStream.toByteArray()), containsString("line1"));
+        assertThat(new String(outputStream.toByteArray()), containsString("line2"));
+    }
+
     @Test
     public void shouldSearchInFiles() throws Exception {
         // given