Fix report output to truncate existing files

CHANGELOG.md

@@ -8,6 +8,7 @@ Currently the versioning policy of this project follows [Semantic Versioning v2.
 ### Fixed
 - Fixed spotbugs build with ecj compiler ([#1903](https://github.com/spotbugs/spotbugs/issues/1903))
 - Moved tests from spotbugs project to spotbugs-tests project ([#1914](https://github.com/spotbugs/spotbugs/issues/1914))
+- Fixed reports to truncate existing files before writing new content ([#1950](https://github.com/spotbugs/spotbugs/issues/1950))
 
 ### Added
 * New detector `FindInstanceLockOnSharedStaticData` for new bug type `SSD_DO_NOT_USE_INSTANCE_LOCK_ON_SHARED_STATIC_DATA`. This detector reports a bug if an instance level lock is used to modify a shared static data. (See [SEI CERT rule LCK06-J](https://wiki.sei.cmu.edu/confluence/display/java/LCK06-J.+Do+not+use+an+instance+lock+to+protect+shared+static+data))

spotbugs-tests/src/test/java/edu/umd/cs/findbugs/TextUICommandLineTest.java

@@ -36,6 +36,19 @@ public void handleOutputFilePathUsesGzip() throws IOException {
         assertThat("GZip file should have -117 as its header", written[1], is((byte) -117));
     }
 
+    @Test
+    public void handleOutputFileTruncatesExisting() throws IOException {
+        Path file = Files.createTempFile("spotbugs", ".html");
+        Files.writeString(file, "content");
+        TextUICommandLine commandLine = new TextUICommandLine();
+        SortingBugReporter reporter = new SortingBugReporter();
+        commandLine.handleOutputFilePath(reporter, "withMessages=" + file.toFile().getAbsolutePath());
+
+        reporter.finish();
+        byte[] written = Files.readAllBytes(file);
+        assertThat("Output file should be truncated to 0 bytes", written.length, is(0));
+    }
+
     @Test
     public void htmlReportWithOption() throws IOException {
         Path xmlFile = Files.createTempFile("spotbugs", ".xml");

spotbugs/src/main/java/edu/umd/cs/findbugs/TextUICommandLine.java

@@ -278,7 +278,8 @@ public boolean justPrintVersion() {
         if (index >= 0) {
             Path path = Paths.get(optionExtraPart.substring(index + 1));
             try {
-                OutputStream oStream = Files.newOutputStream(path, StandardOpenOption.CREATE, StandardOpenOption.WRITE);
+                OutputStream oStream = Files.newOutputStream(path, StandardOpenOption.CREATE, StandardOpenOption.WRITE,
+                        StandardOpenOption.TRUNCATE_EXISTING);
                 if ("gz".equals(Util.getFileExtension(path.toFile()))) {
                     oStream = new GZIPOutputStream(oStream);
                 }