HADOOP-13628. Support to retrieve specific property from configuration via REST API. Contributed by Weiwei Yang

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/ConfServlet.java

@@ -70,11 +70,14 @@ public class ConfServlet extends HttpServlet {
       response.setContentType("application/json; charset=utf-8");
     }
 
+    String name = request.getParameter("name");
     Writer out = response.getWriter();
     try {
-      writeResponse(getConfFromContext(), out, format);
+      writeResponse(getConfFromContext(), out, format, name);
     } catch (BadFormatException bfe) {
       response.sendError(HttpServletResponse.SC_BAD_REQUEST, bfe.getMessage());
+    } catch (IllegalArgumentException iae) {
+      response.sendError(HttpServletResponse.SC_NOT_FOUND, iae.getMessage());
     }
     out.close();
   }
@@ -89,17 +92,23 @@ public class ConfServlet extends HttpServlet {
   /**
    * Guts of the servlet - extracted for easy testing.
    */
-  static void writeResponse(Configuration conf, Writer out, String format)
-    throws IOException, BadFormatException {
+  static void writeResponse(Configuration conf,
+      Writer out, String format, String propertyName)
+          throws IOException, IllegalArgumentException, BadFormatException {
     if (FORMAT_JSON.equals(format)) {
-      Configuration.dumpConfiguration(conf, out);
+      Configuration.dumpConfiguration(conf, propertyName, out);
     } else if (FORMAT_XML.equals(format)) {
-      conf.writeXml(out);
+      conf.writeXml(propertyName, out);
     } else {
       throw new BadFormatException("Bad format: " + format);
     }
   }
 
+  static void writeResponse(Configuration conf, Writer out, String format)
+      throws IOException, BadFormatException {
+    writeResponse(conf, out, format, null);
+  }
+
   public static class BadFormatException extends Exception {
     private static final long serialVersionUID = 1L;
 

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java

@@ -103,8 +103,9 @@ import org.w3c.dom.Text;
 import org.xml.sax.SAXException;
 
 import com.google.common.base.Preconditions;
+import com.google.common.base.Strings;
 
-/** 
+/**
  * Provides access to configuration parameters.
  *
  * <h4 id="Resources">Resources</h4>
@@ -2834,14 +2835,37 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
     writeXml(new OutputStreamWriter(out, "UTF-8"));
   }
 
-  /** 
-   * Write out the non-default properties in this configuration to the given
-   * {@link Writer}.
-   * 
+  public void writeXml(Writer out) throws IOException {
+    writeXml(null, out);
+  }
+
+  /**
+   * Write out the non-default properties in this configuration to the
+   * given {@link Writer}.
+   *
+   * <li>
+   * When property name is not empty and the property exists in the
+   * configuration, this method writes the property and its attributes
+   * to the {@link Writer}.
+   * </li>
+   * <p>
+   *
+   * <li>
+   * When property name is null or empty, this method writes all the
+   * configuration properties and their attributes to the {@link Writer}.
+   * </li>
+   * <p>
+   *
+   * <li>
+   * When property name is not empty but the property doesn't exist in
+   * the configuration, this method throws an {@link IllegalArgumentException}.
+   * </li>
+   * <p>
    * @param out the writer to write to.
    */
-  public void writeXml(Writer out) throws IOException {
-    Document doc = asXmlDocument();
+  public void writeXml(String propertyName, Writer out)
+      throws IOException, IllegalArgumentException {
+    Document doc = asXmlDocument(propertyName);
 
     try {
       DOMSource source = new DOMSource(doc);
@@ -2861,62 +2885,180 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
   /**
    * Return the XML DOM corresponding to this Configuration.
    */
-  private synchronized Document asXmlDocument() throws IOException {
+  private synchronized Document asXmlDocument(String propertyName)
+      throws IOException, IllegalArgumentException {
     Document doc;
     try {
-      doc =
-        DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
+      doc = DocumentBuilderFactory
+          .newInstance()
+          .newDocumentBuilder()
+          .newDocument();
     } catch (ParserConfigurationException pe) {
       throw new IOException(pe);
     }
+
     Element conf = doc.createElement("configuration");
     doc.appendChild(conf);
     conf.appendChild(doc.createTextNode("\n"));
     handleDeprecation(); //ensure properties is set and deprecation is handled
-    for (Enumeration<Object> e = properties.keys(); e.hasMoreElements();) {
-      String name = (String)e.nextElement();
-      Object object = properties.get(name);
-      String value = null;
-      if (object instanceof String) {
-        value = (String) object;
-      }else {
-        continue;
-      }
-      Element propNode = doc.createElement("property");
-      conf.appendChild(propNode);
-
-      Element nameNode = doc.createElement("name");
-      nameNode.appendChild(doc.createTextNode(name));
-      propNode.appendChild(nameNode);
-
-      Element valueNode = doc.createElement("value");
-      valueNode.appendChild(doc.createTextNode(value));
-      propNode.appendChild(valueNode);
-
-      if (updatingResource != null) {
-        String[] sources = updatingResource.get(name);
-        if(sources != null) {
-          for(String s : sources) {
-            Element sourceNode = doc.createElement("source");
-            sourceNode.appendChild(doc.createTextNode(s));
-            propNode.appendChild(sourceNode);
+
+    if(!Strings.isNullOrEmpty(propertyName)) {
+      if (!properties.containsKey(propertyName)) {
+        // given property not found, illegal argument
+        throw new IllegalArgumentException("Property " +
+            propertyName + " not found");
+      } else {
+        // given property is found, write single property
+        appendXMLProperty(doc, conf, propertyName);
+        conf.appendChild(doc.createTextNode("\n"));
+      }
+    } else {
+      // append all elements
+      for (Enumeration<Object> e = properties.keys(); e.hasMoreElements();) {
+        appendXMLProperty(doc, conf, (String)e.nextElement());
+        conf.appendChild(doc.createTextNode("\n"));
+      }
+    }
+    return doc;
+  }
+
+  /**
+   *  Append a property with its attributes to a given {#link Document}
+   *  if the property is found in configuration.
+   *
+   * @param doc
+   * @param conf
+   * @param propertyName
+   */
+  private synchronized void appendXMLProperty(Document doc, Element conf,
+      String propertyName) {
+    // skip writing if given property name is empty or null
+    if (!Strings.isNullOrEmpty(propertyName)) {
+      String value = properties.getProperty(propertyName);
+      if (value != null) {
+        Element propNode = doc.createElement("property");
+        conf.appendChild(propNode);
+
+        Element nameNode = doc.createElement("name");
+        nameNode.appendChild(doc.createTextNode(propertyName));
+        propNode.appendChild(nameNode);
+
+        Element valueNode = doc.createElement("value");
+        valueNode.appendChild(doc.createTextNode(
+            properties.getProperty(propertyName)));
+        propNode.appendChild(valueNode);
+
+        Element finalNode = doc.createElement("final");
+        finalNode.appendChild(doc.createTextNode(
+            String.valueOf(finalParameters.contains(propertyName))));
+        propNode.appendChild(finalNode);
+
+        if (updatingResource != null) {
+          String[] sources = updatingResource.get(propertyName);
+          if(sources != null) {
+            for(String s : sources) {
+              Element sourceNode = doc.createElement("source");
+              sourceNode.appendChild(doc.createTextNode(s));
+              propNode.appendChild(sourceNode);
+            }
           }
         }
       }
-      
-      conf.appendChild(doc.createTextNode("\n"));
     }
-    return doc;
   }
 
   /**
-   *  Writes out all the parameters and their properties (final and resource) to
-   *  the given {@link Writer}
-   *  The format of the output would be 
-   *  { "properties" : [ {key1,value1,key1.isFinal,key1.resource}, {key2,value2,
-   *  key2.isFinal,key2.resource}... ] } 
-   *  It does not output the parameters of the configuration object which is 
-   *  loaded from an input stream.
+   *  Writes properties and their attributes (final and resource)
+   *  to the given {@link Writer}.
+   *
+   *  <li>
+   *  When propertyName is not empty, and the property exists
+   *  in the configuration, the format of the output would be,
+   *  <pre>
+   *  {
+   *    "property": {
+   *      "key" : "key1",
+   *      "value" : "value1",
+   *      "isFinal" : "key1.isFinal",
+   *      "resource" : "key1.resource"
+   *    }
+   *  }
+   *  </pre>
+   *  </li>
+   *
+   *  <li>
+   *  When propertyName is null or empty, it behaves same as
+   *  {@link #dumpConfiguration(Configuration, Writer)}, the
+   *  output would be,
+   *  <pre>
+   *  { "properties" :
+   *      [ { key : "key1",
+   *          value : "value1",
+   *          isFinal : "key1.isFinal",
+   *          resource : "key1.resource" },
+   *        { key : "key2",
+   *          value : "value2",
+   *          isFinal : "ke2.isFinal",
+   *          resource : "key2.resource" }
+   *       ]
+   *   }
+   *  </pre>
+   *  </li>
+   *
+   *  <li>
+   *  When propertyName is not empty, and the property is not
+   *  found in the configuration, this method will throw an
+   *  {@link IllegalArgumentException}.
+   *  </li>
+   *  <p>
+   * @param config the configuration
+   * @param propertyName property name
+   * @param out the Writer to write to
+   * @throws IOException
+   * @throws IllegalArgumentException when property name is not
+   *   empty and the property is not found in configuration
+   **/
+  public static void dumpConfiguration(Configuration config,
+      String propertyName, Writer out) throws IOException {
+    if(Strings.isNullOrEmpty(propertyName)) {
+      dumpConfiguration(config, out);
+    } else if (Strings.isNullOrEmpty(config.get(propertyName))) {
+      throw new IllegalArgumentException("Property " +
+          propertyName + " not found");
+    } else {
+      JsonFactory dumpFactory = new JsonFactory();
+      JsonGenerator dumpGenerator = dumpFactory.createJsonGenerator(out);
+      dumpGenerator.writeStartObject();
+      dumpGenerator.writeFieldName("property");
+      appendJSONProperty(dumpGenerator, config, propertyName);
+      dumpGenerator.writeEndObject();
+      dumpGenerator.flush();
+    }
+  }
+
+  /**
+   *  Writes out all properties and their attributes (final and resource) to
+   *  the given {@link Writer}, the format of the output would be,
+   *
+   *  <pre>
+   *  { "properties" :
+   *      [ { key : "key1",
+   *          value : "value1",
+   *          isFinal : "key1.isFinal",
+   *          resource : "key1.resource" },
+   *        { key : "key2",
+   *          value : "value2",
+   *          isFinal : "ke2.isFinal",
+   *          resource : "key2.resource" }
+   *       ]
+   *   }
+   *  </pre>
+   *
+   *  It does not output the properties of the configuration object which
+   *  is loaded from an input stream.
+   *  <p>
+   *
+   * @param config the configuration
    * @param out the Writer to write to
    * @throws IOException
    */
@@ -2930,29 +3072,47 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
     dumpGenerator.flush();
     synchronized (config) {
       for (Map.Entry<Object,Object> item: config.getProps().entrySet()) {
-        dumpGenerator.writeStartObject();
-        dumpGenerator.writeStringField("key", (String) item.getKey());
-        dumpGenerator.writeStringField("value", 
-                                       config.get((String) item.getKey()));
-        dumpGenerator.writeBooleanField("isFinal",
-                                        config.finalParameters.contains(item.getKey()));
-        String[] resources = config.updatingResource.get(item.getKey());
-        String resource = UNKNOWN_RESOURCE;
-        if(resources != null && resources.length > 0) {
-          resource = resources[0];
-        }
-        dumpGenerator.writeStringField("resource", resource);
-        dumpGenerator.writeEndObject();
+        appendJSONProperty(dumpGenerator,
+            config,
+            item.getKey().toString());
       }
     }
     dumpGenerator.writeEndArray();
     dumpGenerator.writeEndObject();
     dumpGenerator.flush();
   }
-  
+
+  /**
+   * Write property and its attributes as json format to given
+   * {@link JsonGenerator}.
+   *
+   * @param jsonGen json writer
+   * @param config configuration
+   * @param name property name
+   * @throws IOException
+   */
+  private static void appendJSONProperty(JsonGenerator jsonGen,
+      Configuration config, String name) throws IOException {
+    // skip writing if given property name is empty or null
+    if(!Strings.isNullOrEmpty(name) && jsonGen != null) {
+      jsonGen.writeStartObject();
+      jsonGen.writeStringField("key", name);
+      jsonGen.writeStringField("value", config.get(name));
+      jsonGen.writeBooleanField("isFinal",
+          config.finalParameters.contains(name));
+      String[] resources = config.updatingResource.get(name);
+      String resource = UNKNOWN_RESOURCE;
+      if(resources != null && resources.length > 0) {
+        resource = resources[0];
+      }
+      jsonGen.writeStringField("resource", resource);
+      jsonGen.writeEndObject();
+    }
+  }
+
   /**
    * Get the {@link ClassLoader} for this job.
-   * 
+   *
    * @return the correct class loader.
    */
   public ClassLoader getClassLoader() {

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestConfServlet.java

@@ -18,11 +18,15 @@
 package org.apache.hadoop.conf;
 
 import java.io.StringWriter;
+import java.io.PrintWriter;
 import java.io.StringReader;
 import java.util.HashMap;
 import java.util.Map;
 
 import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import javax.servlet.ServletConfig;
+import javax.servlet.ServletContext;
 import javax.ws.rs.core.HttpHeaders;
 import javax.xml.parsers.DocumentBuilder;
 import javax.xml.parsers.DocumentBuilderFactory;
@@ -34,17 +38,36 @@ import org.w3c.dom.Node;
 import org.w3c.dom.NodeList;
 import org.xml.sax.InputSource;
 
-import junit.framework.TestCase;
+import com.google.common.base.Strings;
+
+import org.apache.hadoop.http.HttpServer2;
+import org.junit.BeforeClass;
 import org.junit.Test;
 import org.mockito.Mockito;
+import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.mock;
+import static org.junit.Assert.*;
 
 /**
  * Basic test case that the ConfServlet can write configuration
  * to its output in XML and JSON format.
  */
-public class TestConfServlet extends TestCase {
+public class TestConfServlet {
   private static final String TEST_KEY = "testconfservlet.key";
   private static final String TEST_VAL = "testval";
+  private static final Map<String, String> TEST_PROPERTIES =
+      new HashMap<String, String>();
+  private static final Map<String, String> TEST_FORMATS =
+      new HashMap<String, String>();
+
+  @BeforeClass
+  public static void initTestProperties() {
+    TEST_PROPERTIES.put("test.key1", "value1");
+    TEST_PROPERTIES.put("test.key2", "value2");
+    TEST_PROPERTIES.put("test.key3", "value3");
+    TEST_FORMATS.put(ConfServlet.FORMAT_XML, "application/xml");
+    TEST_FORMATS.put(ConfServlet.FORMAT_JSON, "application/json");
+  }
 
   private Configuration getTestConf() {
     Configuration testConf = new Configuration();
@@ -52,6 +75,14 @@ public class TestConfServlet extends TestCase {
     return testConf;
   }
 
+  private Configuration getMultiPropertiesConf() {
+    Configuration testConf = new Configuration(false);
+    for(String key : TEST_PROPERTIES.keySet()) {
+      testConf.set(key, TEST_PROPERTIES.get(key));
+    }
+    return testConf;
+  }
+
   @Test
   public void testParseHeaders() throws Exception {
     HashMap<String, String> verifyMap = new HashMap<String, String>();
@@ -71,6 +102,92 @@ public class TestConfServlet extends TestCase {
     }
   }
 
+  private void verifyGetProperty(Configuration conf, String format,
+      String propertyName) throws Exception {
+    StringWriter sw = null;
+    PrintWriter pw = null;
+    ConfServlet service = null;
+    try {
+      service = new ConfServlet();
+      ServletConfig servletConf = mock(ServletConfig.class);
+      ServletContext context = mock(ServletContext.class);
+      service.init(servletConf);
+      when(context.getAttribute(HttpServer2.CONF_CONTEXT_ATTRIBUTE))
+        .thenReturn(conf);
+      when(service.getServletContext())
+        .thenReturn(context);
+
+      HttpServletRequest request = mock(HttpServletRequest.class);
+      when(request.getHeader(HttpHeaders.ACCEPT))
+        .thenReturn(TEST_FORMATS.get(format));
+      when(request.getParameter("name"))
+        .thenReturn(propertyName);
+
+      HttpServletResponse response = mock(HttpServletResponse.class);
+      sw = new StringWriter();
+      pw = new PrintWriter(sw);
+      when(response.getWriter()).thenReturn(pw);
+
+      // response request
+      service.doGet(request, response);
+      String result = sw.toString().trim();
+
+      // if property name is null or empty, expect all properties
+      // in the response
+      if (Strings.isNullOrEmpty(propertyName)) {
+        for(String key : TEST_PROPERTIES.keySet()) {
+          assertTrue(result.contains(key) &&
+              result.contains(TEST_PROPERTIES.get(key)));
+        }
+      } else {
+        if(conf.get(propertyName) != null) {
+          // if property name is not empty and property is found
+          assertTrue(result.contains(propertyName));
+          for(String key : TEST_PROPERTIES.keySet()) {
+            if(!key.equals(propertyName)) {
+              assertFalse(result.contains(key));
+            }
+          }
+        } else {
+          // if property name is not empty, and it's not in configuration
+          // expect proper error code and error message is set to the response
+          Mockito.verify(response).sendError(
+              Mockito.eq(HttpServletResponse.SC_NOT_FOUND),
+              Mockito.eq("Property " + propertyName + " not found"));
+        }
+      }
+    } finally {
+      if (sw != null) {
+        sw.close();
+      }
+      if (pw != null) {
+        pw.close();
+      }
+      if (service != null) {
+        service.destroy();
+      }
+    }
+  }
+
+  @Test
+  public void testGetProperty() throws Exception {
+    Configuration configurations = getMultiPropertiesConf();
+    // list various of property names
+    String[] testKeys = new String[] {
+        "test.key1",
+        "test.unknown.key",
+        "",
+        "test.key2",
+        null
+    };
+
+    for(String format : TEST_FORMATS.keySet()) {
+      for(String key : testKeys) {
+        verifyGetProperty(configurations, format, key);
+      }
+    }
+  }
+
   @Test
   @SuppressWarnings("unchecked")
   public void testWriteJson() throws Exception {
@@ -109,7 +226,6 @@ public class TestConfServlet extends TestCase {
     for (int i = 0; i < nameNodes.getLength(); i++) {
       Node nameNode = nameNodes.item(i);
       String key = nameNode.getTextContent();
-      System.err.println("xml key: " + key);
       if (TEST_KEY.equals(key)) {
         foundSetting = true;
         Element propertyElem = (Element)nameNode.getParentNode();

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestConfiguration.java

@@ -42,7 +42,6 @@ import static java.util.concurrent.TimeUnit.*;
 
 import junit.framework.TestCase;
 import static org.junit.Assert.assertArrayEquals;
-import static org.junit.Assert.fail;
 
 import org.apache.commons.lang.StringUtils;
 import org.apache.hadoop.conf.Configuration.IntegerRanges;
@@ -1140,7 +1139,19 @@ public class TestConfiguration extends TestCase {
       this.properties = properties;
     }
   }
-  
+
+  static class SingleJsonConfiguration {
+    private JsonProperty property;
+
+    public JsonProperty getProperty() {
+      return property;
+    }
+
+    public void setProperty(JsonProperty property) {
+      this.property = property;
+    }
+  }
+
   static class JsonProperty {
     String key;
     public String getKey() {
@@ -1171,7 +1182,14 @@ public class TestConfiguration extends TestCase {
     boolean isFinal;
     String resource;
   }
-  
+
+  private Configuration getActualConf(String xmlStr) {
+    Configuration ac = new Configuration(false);
+    InputStream in = new ByteArrayInputStream(xmlStr.getBytes());
+    ac.addResource(in);
+    return ac;
+  }
+
   public void testGetSetTrimmedNames() throws IOException {
     Configuration conf = new Configuration(false);
     conf.set(" name", "value");
@@ -1180,7 +1198,121 @@ public class TestConfiguration extends TestCase {
     assertEquals("value", conf.getRaw("  name  "));
   }
 
-  public void testDumpConfiguration () throws IOException {
+  public void testDumpProperty() throws IOException {
+    StringWriter outWriter = new StringWriter();
+    ObjectMapper mapper = new ObjectMapper();
+    String jsonStr = null;
+    String xmlStr = null;
+    try {
+      Configuration testConf = new Configuration(false);
+      out = new BufferedWriter(new FileWriter(CONFIG));
+      startConfig();
+      appendProperty("test.key1", "value1");
+      appendProperty("test.key2", "value2", true);
+      appendProperty("test.key3", "value3");
+      endConfig();
+      Path fileResource = new Path(CONFIG);
+      testConf.addResource(fileResource);
+      out.close();
+
+      // case 1: dump an existing property
+      // test json format
+      outWriter = new StringWriter();
+      Configuration.dumpConfiguration(testConf, "test.key2", outWriter);
+      jsonStr = outWriter.toString();
+      outWriter.close();
+      mapper = new ObjectMapper();
+      SingleJsonConfiguration jconf1 =
+          mapper.readValue(jsonStr, SingleJsonConfiguration.class);
+      JsonProperty jp1 = jconf1.getProperty();
+      assertEquals("test.key2", jp1.getKey());
+      assertEquals("value2", jp1.getValue());
+      assertEquals(true, jp1.isFinal);
+      assertEquals(fileResource.toUri().getPath(), jp1.getResource());
+
+      // test xml format
+      outWriter = new StringWriter();
+      testConf.writeXml("test.key2", outWriter);
+      xmlStr = outWriter.toString();
+      outWriter.close();
+      Configuration actualConf1 = getActualConf(xmlStr);
+      assertEquals(1, actualConf1.size());
+      assertEquals("value2", actualConf1.get("test.key2"));
+      assertTrue(actualConf1.getFinalParameters().contains("test.key2"));
+      assertEquals(fileResource.toUri().getPath(),
+          actualConf1.getPropertySources("test.key2")[0]);
+
+      // case 2: dump an non existing property
+      // test json format
+      try {
+        outWriter = new StringWriter();
+        Configuration.dumpConfiguration(testConf,
+            "test.unknown.key", outWriter);
+        outWriter.close();
+      } catch (Exception e) {
+        assertTrue(e instanceof IllegalArgumentException);
+        assertTrue(e.getMessage().contains("test.unknown.key") &&
+            e.getMessage().contains("not found"));
+      }
+      // test xml format
+      try {
+        outWriter = new StringWriter();
+        testConf.writeXml("test.unknown.key", outWriter);
+        outWriter.close();
+      } catch (Exception e) {
+        assertTrue(e instanceof IllegalArgumentException);
+        assertTrue(e.getMessage().contains("test.unknown.key") &&
+            e.getMessage().contains("not found"));
+      }
+
+      // case 3: specify a null property, ensure all configurations are dumped
+      outWriter = new StringWriter();
+      Configuration.dumpConfiguration(testConf, null, outWriter);
+      jsonStr = outWriter.toString();
+      mapper = new ObjectMapper();
+      JsonConfiguration jconf3 =
+          mapper.readValue(jsonStr, JsonConfiguration.class);
+      assertEquals(3, jconf3.getProperties().length);
+
+      outWriter = new StringWriter();
+      testConf.writeXml(null, outWriter);
+      xmlStr = outWriter.toString();
+      outWriter.close();
+      Configuration actualConf3 = getActualConf(xmlStr);
+      assertEquals(3, actualConf3.size());
+      assertTrue(actualConf3.getProps().containsKey("test.key1") &&
+          actualConf3.getProps().containsKey("test.key2") &&
+          actualConf3.getProps().containsKey("test.key3"));
+
+      // case 4: specify an empty property, ensure all configurations are dumped
+      outWriter = new StringWriter();
+      Configuration.dumpConfiguration(testConf, "", outWriter);
+      jsonStr = outWriter.toString();
+      mapper = new ObjectMapper();
+      JsonConfiguration jconf4 =
+          mapper.readValue(jsonStr, JsonConfiguration.class);
+      assertEquals(3, jconf4.getProperties().length);
+
+      outWriter = new StringWriter();
+      testConf.writeXml("", outWriter);
+      xmlStr = outWriter.toString();
+      outWriter.close();
+      Configuration actualConf4 = getActualConf(xmlStr);
+      assertEquals(3, actualConf4.size());
+      assertTrue(actualConf4.getProps().containsKey("test.key1") &&
+          actualConf4.getProps().containsKey("test.key2") &&
+          actualConf4.getProps().containsKey("test.key3"));
+    } finally {
+      if(outWriter != null) {
+        outWriter.close();
+      }
+      if(out != null) {
+        out.close();
+      }
+    }
+  }
+
+  public void testDumpConfiguration() throws IOException {
     StringWriter outWriter = new StringWriter();
     Configuration.dumpConfiguration(conf, outWriter);
     String jsonStr = outWriter.toString();