java_gen: beautify toString output of OFMatch
diff --git a/java_gen/templates/custom/OFMatch_toString.java b/java_gen/templates/custom/OFMatch_toString.java
new file mode 100644
index 0000000..1eaf8a5
--- /dev/null
+++ b/java_gen/templates/custom/OFMatch_toString.java
@@ -0,0 +1,18 @@
+    @Override
+    public String toString() {
+        StringBuilder b = new StringBuilder("${msg.name}(");
+        boolean first = true;
+        for(MatchField<?> field : getMatchFields()) {
+            if(first)
+                first = false;
+            else
+                b.append(", ");
+            String name = field.getName();
+            b.append(name).append('=').append(this.get(field));
+            if(isPartiallyMasked(field)) {
+                b.append('/').append(this.getMasked(field).getMask());
+            }
+        }
+        b.append(")");
+        return b.toString();
+    }