nosqlbench-1130 Add a collection joining function

virtdata-lib-basics/src/main/java/io/nosqlbench/virtdata/library/basics/shared/from_long/to_string/Join.java

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+/*
+ * Copyright (c) 2023 nosqlbench
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.nosqlbench.virtdata.library.basics.shared.from_long.to_string;
+
+import io.nosqlbench.virtdata.api.annotations.Categories;
+import io.nosqlbench.virtdata.api.annotations.Category;
+import io.nosqlbench.virtdata.api.annotations.Example;
+import io.nosqlbench.virtdata.api.annotations.ThreadSafeMapper;
+
+import java.util.Collection;
+import java.util.function.Function;
+
+/**
+ * This takes any collection and concatenates the String representation
+ * with a specified delimiter.
+ */
+@Categories({Category.general,Category.collections})
+@ThreadSafeMapper
+public class Join<T> implements Function<Collection<T>,String> {
+
+    private final ThreadLocal<StringBuilder> tlsb = ThreadLocal.withInitial(() -> new StringBuilder());
+    private final String delim;
+    private final int delimBackstep;
+
+    @Example({"Join(',')","Concatenate the incoming collection with ','"})
+    public Join(String delim) {
+        this.delim = delim;
+        this.delimBackstep = delim.length();
+    }
+
+    @Override
+    public String apply(Collection<T> collection) {
+        StringBuilder sb = tlsb.get();
+        sb.setLength(0);
+        for (T value : collection) {
+            sb.append(value.toString());
+            sb.append(delim);
+        }
+        sb.setLength(sb.length()-delimBackstep);
+        return sb.toString();
+    }
+}

virtdata-lib-basics/src/test/java/io/nosqlbench/virtdata/library/basics/shared/from_long/to_string/JoinTest.java

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+/*
+ * Copyright (c) 2023 nosqlbench
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.nosqlbench.virtdata.library.basics.shared.from_long.to_string;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+
+public class JoinTest {
+
+    @Test
+    public void testWithLists() {
+        Join joiner = new Join(",");
+        assertThat(joiner.apply(List.of("one","two"))).isEqualTo("one,two");
+    }
+}