add ISSN example

README.adoc

@@ -122,7 +122,6 @@ try (MarcJsonWriter writer = new MarcJsonWriter("bulk%d.jsonl.gz", 10000,
             .writeCollection();
 
 }
-
 ----
 
 where the result can be indexed by a simple bash script using `curl`, because our JSON
@@ -148,6 +147,73 @@ By executing `curl localhost:9200/_search?pretty` you can examine the result.
 
 image:{img}/marcxchange-in-elasticsearch.png[]
 
+### Example: finding all ISSNs
+
+This Java program scans through a MARC file, checks for ISSN values, and collects them in
+JSON format (the library `org.xbib:content-core:1.0.7` is used for JSON formatting)
+
+[source,java]
+----
+public void findISSNs() throws IOException {
+    Map<String, List<Map<String, String>>> result = new TreeMap<>();
+    // set up MARC listener
+    MarcListener marcListener = new MarcFieldAdapter() {
+        @Override
+        public void field(MarcField field) {
+            Collection<Map<String, String>> values = field.getSubfields().stream()
+                    .filter(f -> matchISSNField(field, f))
+                    .map(f -> Collections.singletonMap(f.getId(), f.getValue()))
+                    .collect(Collectors.toList());
+            if (!values.isEmpty()) {
+                result.putIfAbsent(field.getTag(), new ArrayList<>());
+                List<Map<String, String>> list = result.get(field.getTag());
+                list.addAll(values);
+                result.put(field.getTag(), list);
+            }
+        }
+    };
+    // read MARC file
+    Marc.builder()
+            .setInputStream(getClass().getResource("issns.mrc").openStream())
+            .setMarcListener(marcListener)
+            .build()
+            .writeCollection();
+    // collect ISSNs
+    List<String> issns = result.values().stream()
+            .map(l -> l.stream()
+                    .map(m -> m.values().iterator().next())
+                    .collect(Collectors.toList()))
+            .flatMap(List::stream)
+            .distinct()
+            .collect(Collectors.toList());
+
+    // JSON output
+    XContentBuilder builder = contentBuilder().prettyPrint()
+            .startObject();
+    for (Map.Entry<String, List<Map<String, String>>> entry : result.entrySet()) {
+        builder.field(entry.getKey(), entry.getValue());
+    }
+    builder.array("issns", issns);
+    builder.endObject();
+
+    logger.log(Level.INFO, builder.string());
+}
+
+private static boolean matchISSNField(MarcField field, MarcField.Subfield subfield) {
+    switch (field.getTag()) {
+        case "011": {
+            return "a".equals(subfield.getId()) || "f".equals(subfield.getId());
+        }
+        case "421":
+        case "451":
+        case "452":
+        case "488":
+            return "x".equals(subfield.getId());
+    }
+    return false;
+}
+----
+
 ## Bibliographic character sets
 
 Bibliographic character sets predate the era of Unicode. Before Unicode, characters sets were

build.gradle

@@ -40,6 +40,7 @@ dependencies {
     testCompile "org.xmlunit:xmlunit-matchers:${project.property('xmlunit-matchers.version')}"
     testCompile "com.github.stefanbirkner:system-rules:${project.property('system-rules.version')}"
     testCompile "org.xbib:bibliographic-character-sets:${project.property('bibliographic-character-sets.version')}"
+    testCompile "org.xbib:content-core:${project.property('content-core.version')}"
     asciidoclet "org.asciidoctor:asciidoclet:${project.property('asciidoclet.version')}"
     wagon "org.apache.maven.wagon:wagon-ssh-external:${project.property('wagon-ssh-external.version')}"
 }

gradle.properties

@@ -1,11 +1,12 @@
 group = org.xbib
 name = marc
-version = 1.0.10
+version = 1.0.11
 
 junit.version = 4.12
 xalan.version = 2.7.2
 xmlunit-matchers.version = 2.3.0
 system-rules.version = 1.16.0
 bibliographic-character-sets.version = 1.0.0
+content-core.version = 1.0.7
 asciidoclet.version = 1.5.4
 wagon-ssh-external.version = 2.10

src/main/java/org/xbib/marc/MarcFieldAdapter.java

@@ -0,0 +1,46 @@
+/*
+   Copyright 2016 Jörg Prante
+
+   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 org.xbib.marc;
+
+/**
+ * A MARC listener with empty methods. Useful for extending.
+ */
+public class MarcFieldAdapter implements  MarcListener {
+    @Override
+    public void beginCollection() {
+    }
+
+    @Override
+    public void beginRecord(String format, String type) {
+    }
+
+    @Override
+    public void leader(String label) {
+    }
+
+    @Override
+    public void field(MarcField field) {
+    }
+
+    @Override
+    public void endRecord() {
+    }
+
+    @Override
+    public void endCollection() {
+    }
+}

src/test/java/org/xbib/marc/filter/MarcFieldFilterTest.java

@@ -0,0 +1,91 @@
+package org.xbib.marc.filter;
+
+import static org.xbib.content.json.JsonXContent.contentBuilder;
+
+import org.junit.Test;
+import org.xbib.content.XContentBuilder;
+import org.xbib.marc.Marc;
+import org.xbib.marc.MarcField;
+import org.xbib.marc.MarcFieldAdapter;
+import org.xbib.marc.MarcListener;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import java.util.stream.Collectors;
+
+/**
+ * Demo of collecting ISSNs from a MARC file.
+ *
+ * "issns.mrc" courtesy of Steven Hirren (steven.hirren.gmail.com)
+ */
+public class MarcFieldFilterTest {
+
+    private static final Logger logger = Logger.getLogger(MarcFieldFilterTest.class.getName());
+
+    @Test
+    public void findISSNs() throws IOException {
+        Map<String, List<Map<String, String>>> result = new TreeMap<>();
+        // set up MARC listener
+        MarcListener marcListener = new MarcFieldAdapter() {
+            @Override
+            public void field(MarcField field) {
+                Collection<Map<String, String>> values = field.getSubfields().stream()
+                        .filter(f -> matchISSNField(field, f))
+                        .map(f -> Collections.singletonMap(f.getId(), f.getValue()))
+                        .collect(Collectors.toList());
+                if (!values.isEmpty()) {
+                    result.putIfAbsent(field.getTag(), new ArrayList<>());
+                    List<Map<String, String>> list = result.get(field.getTag());
+                    list.addAll(values);
+                    result.put(field.getTag(), list);
+                }
+            }
+        };
+        // read MARC file
+        Marc.builder()
+                .setInputStream(getClass().getResource("issns.mrc").openStream())
+                .setMarcListener(marcListener)
+                .build()
+                .writeCollection();
+        // collect ISSNs
+        List<String> issns = result.values().stream()
+                .map(l -> l.stream()
+                        .map(m -> m.values().iterator().next())
+                        .collect(Collectors.toList()))
+                .flatMap(List::stream)
+                .distinct()
+                .collect(Collectors.toList());
+
+        // JSON output
+        XContentBuilder builder = contentBuilder().prettyPrint()
+                .startObject();
+        for (Map.Entry<String, List<Map<String, String>>> entry : result.entrySet()) {
+            builder.field(entry.getKey(), entry.getValue());
+        }
+        builder.array("issns", issns);
+        builder.endObject();
+
+        logger.log(Level.INFO, builder.string());
+    }
+
+    private static boolean matchISSNField(MarcField field, MarcField.Subfield subfield) {
+        switch (field.getTag()) {
+            case "011": {
+                return "a".equals(subfield.getId()) || "f".equals(subfield.getId());
+            }
+            case "421":
+            case "451":
+            case "452":
+            case "488":
+                return "x".equals(subfield.getId());
+        }
+        return false;
+    }
+}

src/test/resources/org/xbib/marc/filter/issns.mrc

@@ -0,0 +1 @@
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