add MultiStream class

src/main/java/org/cobbzilla/util/io/MultiStream.java

@@ -0,0 +1,74 @@
+package org.cobbzilla.util.io;
+
+import lombok.extern.slf4j.Slf4j;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.ArrayList;
+import java.util.List;
+
+@Slf4j
+public class MultiStream extends InputStream {
+
+    private final List<InputStream> streams = new ArrayList<>();
+    private InputStream currentStream;
+    private int streamIndex = 0;
+    private boolean endOfStreams = false;
+
+    public MultiStream (InputStream r, boolean last) {
+        if (last) {
+            addLastStream(r);
+        } else {
+            addStream(r);
+        }
+        currentStream = r;
+    }
+
+    public MultiStream (InputStream r) { this(r, false); }
+
+    public void addStream (InputStream in) {
+        if (endOfStreams) {
+            log.warn("addStream: endOfStreams is true, not adding InputStream");
+        } else {
+            streams.add(in);
+        }
+    }
+
+    public void addLastStream (InputStream in) {
+        addStream(in);
+        endOfStreams = true;
+    }
+
+    @Override public int read() throws IOException {
+        int val = currentStream.read();
+        if (val == -1) {
+            if (streamIndex == streams.size()-1) {
+                return endOfStreams ? -1 : 0;
+            }
+            currentStream.close();
+            streamIndex++;
+            currentStream = streams.get(streamIndex);
+            return read();
+        }
+        return val;
+    }
+
+    @Override public int read(byte[] buf, int off, int len) throws IOException {
+        int count = currentStream.read(buf, off, len);
+        if (count == -1) {
+            if (streamIndex == streams.size()-1) {
+                return endOfStreams ? -1 : 0;
+            }
+            currentStream.close();
+            streamIndex++;
+            currentStream = streams.get(streamIndex);
+            return read(buf, off, len);
+        }
+        return count;
+    }
+
+    @Override public void close() throws IOException {
+        if (currentStream != null) currentStream.close();
+    }
+
+}