Add a helper method to parse maps of objects

server/src/main/java/org/elasticsearch/common/xcontent/XContentParserUtils.java

@@ -25,7 +25,9 @@
 import org.elasticsearch.common.xcontent.XContentParser.Token;
 
 import java.io.IOException;
+import java.util.HashMap;
 import java.util.Locale;
+import java.util.Map;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
@@ -159,4 +161,36 @@ public static <T> void parseTypedKeysObject(XContentParser parser, String delimi
             throw new ParsingException(parser.getTokenLocation(), "Failed to parse object: empty key");
         }
     }
+
+    /**
+     * Parses a json map of objects into a map
+     *
+     * Each map key is passed as the context to the object parser used to construct
+     * the map values.
+     *
+     * @param p             the XContentParser
+     * @param objectParser  a parser used to construct map values
+     * @param singleton     if {@code true}, then an exception is thrown if the map has more than one key
+     */
+    public static <T> Map<String, T> parseMap(XContentParser p, ContextParser<String, T> objectParser,
+                                              boolean singleton) throws IOException {
+        Map<String, T> map = new HashMap<>();
+        if (p.currentToken() != Token.START_OBJECT) {
+            ensureExpectedToken(Token.START_OBJECT, p.nextToken(), p::getTokenLocation);
+        }
+        while (p.nextToken() != XContentParser.Token.END_OBJECT) {
+            ensureExpectedToken(Token.FIELD_NAME, p.currentToken(), p::getTokenLocation);
+            if (singleton && map.isEmpty() == false) {
+                throw new XContentParseException(p.getTokenLocation(),
+                    "Expected a single field but found [" + map.keySet().iterator().next() + "," + p.currentName() + "]");
+            }
+            String currentField = p.currentName();
+            try {
+                map.put(currentField, objectParser.parse(p, currentField));
+            } catch (Exception e) {
+                throw new XContentParseException(p.getTokenLocation(), "Error parsing field [" + currentField + "]", e);
+            }
+        }
+        return map;
+    }
 }

server/src/test/java/org/elasticsearch/common/xcontent/XContentParserUtilsTests.java

@@ -41,6 +41,8 @@
 import static org.elasticsearch.common.xcontent.XContentParserUtils.parseTypedKeysObject;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.endsWith;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.instanceOf;
 
 public class XContentParserUtilsTests extends ESTestCase {
@@ -253,4 +255,61 @@ public void testParseTypedKeysObjectErrors() throws IOException {
             }
         }
     }
+
+    private static class TestStruct {
+        final String name;
+        String a;
+        long b;
+
+        TestStruct(String name) {
+            this.name = name;
+        }
+    }
+
+    public void testMapParsing() throws IOException {
+
+        ObjectParser<TestStruct, String> structParser = ObjectParser.fromBuilder("test", TestStruct::new);
+        structParser.declareString((t, s) -> t.a = s, new ParseField("a"));
+        structParser.declareLong((t, l) -> t.b = l, new ParseField("b"));
+
+        XContentParser parser = createParser(JsonXContent.jsonXContent,
+            "{ \"label1\" : { \"a\" : \"hello\", \"b\" : 1 }, \"label2\" : { \"a\" : \"world\", \"b\" : 2 } }");
+
+        Map<String, TestStruct> map = XContentParserUtils.parseMap(parser, structParser, false);
+
+        assertThat(map, hasKey("label1"));
+        assertThat(map.get("label1").name, equalTo("label1"));
+        assertThat(map.get("label1").a, equalTo("hello"));
+        assertThat(map.get("label1").b, equalTo(1L));
+        assertThat(map, hasKey("label2"));
+        assertThat(map.get("label2").name, equalTo("label2"));
+        assertThat(map.get("label2").a, equalTo("world"));
+        assertThat(map.get("label2").b, equalTo(2L));
+
+    }
+
+    public void testMapParsingErrors() throws IOException {
+
+        ObjectParser<TestStruct, String> structParser = ObjectParser.fromBuilder("test", TestStruct::new);
+        structParser.declareString((t, s) -> t.a = s, new ParseField("a"));
+        structParser.declareLong((t, l) -> t.b = l, new ParseField("b"));
+
+        {
+            XContentParser parser = createParser(JsonXContent.jsonXContent,
+                "{ \"label1\" : { \"a\" : \"hello\", \"b\" : 1 }, \"label2\" : { \"a\" : \"world\", \"b\" : 2 } }");
+            Exception e = expectThrows(XContentParseException.class, () -> XContentParserUtils.parseMap(parser, structParser, true));
+            assertThat(e.getMessage(), equalTo("[1:42] Expected a single field but found [label1,label2]"));
+        }
+
+        {
+            XContentParser parser = createParser(JsonXContent.jsonXContent,
+                "{ \"label1\" : { \"a\" : \"hello\", \"b\" : 1 }, \"label2\" : { \"a\" : \"world\", \"b\" : \"two\" } }");
+            Exception e = expectThrows(XContentParseException.class, () -> XContentParserUtils.parseMap(parser, structParser, false));
+            assertThat(e.getMessage(), equalTo("[1:76] Error parsing field [label2]"));
+            Throwable t = e.getCause();
+            assertNotNull(t);
+            assertThat(t.getMessage(), containsString("[test] failed to parse field [b]"));
+        }
+
+    }
 }