StreamOutWrapper: add a constructor that takes a StringStream

src/main/java/com/github/stephengold/joltjni/StreamOutWrapper.java

@@ -21,6 +21,8 @@ of this software and associated documentation files (the "Software"), to deal
  */
 package com.github.stephengold.joltjni;
 
+import com.github.stephengold.joltjni.std.StringStream;
+
 /**
  * A wrapper around an {@code std::ofstream}.
  *
@@ -40,6 +42,17 @@ public StreamOutWrapper(String fileName, int streamMode) {
         long streamVa = createStreamOutWrapper(fileName, streamMode);
         setVirtualAddress(streamVa, true);
     }
+
+    /**
+     * Open a {@code StringStream} for output.
+     *
+     * @param data the underlying stream (not null)
+     */
+    public StreamOutWrapper(StringStream data) {
+        long dataVa = data.va();
+        long streamVa = createFromStringStream(dataVa);
+        setVirtualAddress(streamVa, true);
+    }
     // *************************************************************************
     // new methods exposed
 
@@ -89,6 +102,8 @@ public StreamOutWrapper(String fileName, int streamMode) {
     // *************************************************************************
     // native private methods
 
+    native private static long createFromStringStream(long dataVa);
+
     native private static long createStreamOutWrapper(
             String fileName, int streamMode);
 }

src/main/native/glue/s/StreamOutWrapper.cpp

@@ -97,6 +97,20 @@ JNIEXPORT jint JNICALL Java_com_github_stephengold_joltjni_StreamOutWrapper_trun
     return result;
 }
 
+/*
+ * Class:     com_github_stephengold_joltjni_StreamOutWrapper
+ * Method:    createFromStringStream
+ * Signature: (J)J
+ */
+JNIEXPORT jlong JNICALL Java_com_github_stephengold_joltjni_StreamOutWrapper_createFromStringStream
+  (JNIEnv *, jclass, jlong streamVa) {
+    std::stringstream * const pStream
+            = reinterpret_cast<std::stringstream *> (streamVa);
+    StreamOutWrapper * const pResult = new StreamOutWrapper(*pStream);
+    TRACE_NEW("StreamOutWrapper", pResult)
+    return reinterpret_cast<jlong> (pResult);
+}
+
 /*
  * Class:     com_github_stephengold_joltjni_StreamOutWrapper
  * Method:    createStreamOutWrapper