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Java + MongoDB: how get a nested field value using complete path?

I have this path for a MongoDB field main.inner.leaf and every field couldn't be present.
In Java I should write, avoiding null:
String leaf = "";
if (document.get("main") != null &&
document.get("main", Document.class).get("inner") != null) {
leaf = document.get("main", Document.class)
.get("inner", Document.class).getString("leaf");
}
In this simple example I set only 3 levels: main, inner and leaf but my documents are deeper.
So is there a way avoiding me writing all these null checks?
Like this:
String leaf = document.getString("main.inner.leaf", "");
// "" is the deafult value if one of the levels doesn't exist
Or using a third party library:
String leaf = DocumentUtils.getNullCheck("main.inner.leaf", "", document);
Many thanks.

Since the intermediate attributes are optional you really have to access the leaf value in a null safe manner.
You could do this yourself using an approach like ...
if (document.containsKey("main")) {
Document _main = document.get("main", Document.class);
if (_main.containsKey("inner")) {
Document _inner = _main.get("inner", Document.class);
if (_inner.containsKey("leaf")) {
leafValue = _inner.getString("leaf");
}
}
}
Note: this could be wrapped up in a utility to make it more user friendly.
Or use a thirdparty library such as Commons BeanUtils.
But, you cannot avoid null safe checks since the document structure is such that the intermediate levels might be null. All you can do is to ease the burden of handling the null safety.
Here's an example test case showing both approaches:
#Test
public void readNestedDocumentsWithNullSafety() throws IllegalAccessException, NoSuchMethodException, InvocationTargetException {
Document inner = new Document("leaf", "leafValue");
Document main = new Document("inner", inner);
Document fullyPopulatedDoc = new Document("main", main);
assertThat(extractLeafValueManually(fullyPopulatedDoc), is("leafValue"));
assertThat(extractLeafValueUsingThirdPartyLibrary(fullyPopulatedDoc, "main.inner.leaf", ""), is("leafValue"));
Document emptyPopulatedDoc = new Document();
assertThat(extractLeafValueManually(emptyPopulatedDoc), is(""));
assertThat(extractLeafValueUsingThirdPartyLibrary(emptyPopulatedDoc, "main.inner.leaf", ""), is(""));
Document emptyInner = new Document();
Document partiallyPopulatedMain = new Document("inner", emptyInner);
Document partiallyPopulatedDoc = new Document("main", partiallyPopulatedMain);
assertThat(extractLeafValueManually(partiallyPopulatedDoc), is(""));
assertThat(extractLeafValueUsingThirdPartyLibrary(partiallyPopulatedDoc, "main.inner.leaf", ""), is(""));
}
private String extractLeafValueUsingThirdPartyLibrary(Document document, String path, String defaultValue) {
try {
Object value = PropertyUtils.getNestedProperty(document, path);
return value == null ? defaultValue : value.toString();
} catch (Exception ex) {
return defaultValue;
}
}
private String extractLeafValueManually(Document document) {
Document inner = getOrDefault(getOrDefault(document, "main"), "inner");
return inner.get("leaf", "");
}
private Document getOrDefault(Document document, String key) {
if (document.containsKey(key)) {
return document.get(key, Document.class);
} else {
return new Document();
}
}

Java Milo OPC-UA add node

I'm using Milo and its example server and client. I'm adding nodes to the server but I can't figure out how to add EuInformation, i.e., unit and description. I thought about using the ExtensionObject but since EuInformation does not implement Serializable I don't know how to pass it to the ExtensionObject. I'd also like to know how I can get the namespace ID and URI on client side. So far I just set them statically as I have access to the classes.
I've implemeted the AddNodes on server side. I can add nodes, read nodes and write to nodes.
Here's what I'm doing on client side:
// Should somehow get the namespace ID and namespace dynamically.
// Maybe by iterating through all nodes??
ExpandedNodeId parentNodeId = new ExpandedNodeId(
new nodeId(2,DatatypeNamespace.NODE_IDENTIFIER),
datatypeNamespace.NAMESPACE_URI, 0);
NodeId referenceTypeId = Identifiers.String;
// Define the new node.
ExpandedNodeId requestedNewNodeId = new ExpandedNodeId(new NodeId(2, "NewNode"),
DatatypeNamespace.NAMESPACE_URI, 0);
QualifiedName browseName = new QualifiedName(2, "NewNode");
// How to get this to the server??
EUInformation euinfo = new EUInformation(null,-1,LocalizedText.english("MyUnit"),
LocalizedText.english("My Description"));
ExpandedNodeId typeDef = new ExpandedNodeId(Identifiers.BaseVariableType,
DatatypeNamespace.NAMESPACE_URI, 0);
AddNodesItem newItem = new AddNodesItem(parentNodeId, referenceTypeId,
requestedNewNodeId,rowseName,NodeClass.VariableType, null, typeDef);
List<AddNodesItem> items = new ArrayList<AddNodesItem>();
items.add(newItem);
client.addNodes(items).get();
EDIT
With the help of Kevin Herron's answer I worked something out: I adjusted the write() in my namespace class. I can now modify the display name and description of the node with the values of the EUInformation. Here's my write() method:
#Override
public void write(WriteContext context, List<WriteValue> writeValues) {
List<StatusCode> results = Lists.newArrayListWithCapacity(writeValues.size());
for (WriteValue writeValue : writeValues) {
ServerNode node = server.getNodeMap().get(writeValue.getNodeId());
if (node != null) {
// Get the type of the variant thats about to be written to the node
NodeId variantType = writeValue.getValue().getValue().getDataType().get();
if (variantType.equals(Identifiers.Structure)) {
ExtensionObject o = (ExtensionObject) writeValue.getValue().getValue().getValue();
if (o.getEncodingTypeId().equals(Identifiers.EUInformation_Encoding_DefaultBinary)) {
EUInformation euInformation = (EUInformation) o.decode();
node.setDescription(euInformation.getDescription());
node.setDisplayName(euInformation.getDisplayName());
System.out.println("Wrote EUInformation " + euInformation);
results.add(StatusCode.GOOD);
context.complete(results);
return;
}
}
try {
node.writeAttribute(new AttributeContext(context), writeValue.getAttributeId(),
writeValue.getValue(), writeValue.getIndexRange());
results.add(StatusCode.GOOD);
System.out.println(String.format("Wrote value %s to %s attribute of %s",
writeValue.getValue().getValue(),
AttributeId.from(writeValue.getAttributeId()).map(Object::toString).orElse("unknown"),
node.getNodeId()));
} catch (UaException e) {
System.out.println(String.format("Unable to write %s", writeValue.getValue()));
results.add(e.getStatusCode());
}
} else {
results.add(new StatusCode(StatusCodes.Bad_NodeIdUnknown));
}
}
context.complete(results);
}

Ok, so you would add a new VaribleNode with a TypeDefinition of Property (Identifiers.PropertyType).
Then you would write to its Value attribute so it contains the EUInformation object:
EUInformation euInformation = ...
Variant v = new Variant(ExtensionObject.encode(euInformation));
...write the value to the node you created...

Check whether a value exists in a JSON object using Java

I'm very new to Java and trying to find and check whether a particular value exists in JSON object. Here is my code,
String strUsers = representation.getText();
JSONObject jsonObject = new JSONObject(strUsers);
Iterator<String> keys = jsonObj.keys();
while(keys.hasNext()) {
String key = keys.next();
String val = null;
try {
JSONObject value = jsonObj.getJSONObject(key);
} catch(Exception e) {
}
}
Further I'm not able to understand how to check. Can any one guide me in achieving my goal?

You should use the method has.
if(jsonObject.has("your_key")) {
// get the value and do something with it
}
In your try-catch block, before getting the value check if the key actually exists.
if (jsonObject.has(key)) {
// then get the value
JSONObject value = jsonObj.getJSONObject(key);
}

Using ScriptEngine in java, How can I extract function list?

using Jsoup, I extract JavaScript part in html file. and store it as java String Object.
and I want to extract function list, variables list in js's function using javax.script.ScriptEngine
JavaScript part has several function section.
ex)
function a() {
var a_1;
var a_2
...
}
function b() {
var b_1;
var b_2;
...
}
function c() {
var c_1;
var c_2;
...
}
My Goals is right below.
List funcList
a
b
c
List varListA
a_1
a_2
...
List varListB
b_1
b_2
...
List varListC
c_1
c_2
...
How can I extract function list and variables list(or maybe values)?

I think you can do this by using javascript introspection after having loaded the javascript in the Engine - e.g. for functions:
ScriptEngine engine;
// create the engine and have it load your javascript
Bindings bind = engine.getBindings(ScriptContext.ENGINE_SCOPE);
Set<String> allAttributes = bind.keySet();
Set<String> allFunctions = new HashSet<String>();
for ( String attr : allAttributes ) {
if ( "function".equals( engine.eval("typeof " + attr) ) ) {
allFunctions.add(attr);
}
}
System.out.println(allFunctions);
I haven't found a way to extract the variables inside functions (local variables) without delving in internal mechanics (and thus unsafe to use) of the javascript scripting engine.

It is pretty tricky. ScriptEngine API seems not good for inspecting the code. So, I have such kind of pretty ugly solution with instance of and cast operators.
Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
for (Map.Entry<String, Object> scopeEntry : bindings.entrySet()) {
Object value = scopeEntry.getValue();
String name = scopeEntry.getKey();
if (value instanceof NativeFunction) {
log.info("Function -> " + name);
NativeFunction function = NativeFunction.class.cast(value);
DebuggableScript debuggableFunction = function.getDebuggableView();
for (int i = 0; i < debuggableFunction.getParamAndVarCount(); i++) {
log.info("First level arg: " + debuggableFunction.getParamOrVarName(i));
}
} else if (value instanceof Undefined
|| value instanceof String
|| value instanceof Number) {
log.info("Global arg -> " + name);
}
}

I had similar issue. Maybe it will be helpfull for others.
I use groove as script lang. My Task was to retrive all invokable functions from the script. And then filter this functions by some criteria.
Unfortunately this approach is usefull only for groovy...
Get script engine:
public ScriptEngine getEngine() throws Exception {
if (engine == null)
engine = new ScriptEngineManager().getEngineByName(scriptType);
if (engine == null)
throw new Exception("Could not find implementation of " + scriptType);
return engine;
}
Compile and evaluate script:
public void evaluateScript(String script) throws Exception {
Bindings bindings = getEngine().getBindings(ScriptContext.ENGINE_SCOPE);
bindings.putAll(binding);
try {
if (engine instanceof Compilable)
compiledScript = ((Compilable)getEngine()).compile(script);
getEngine().eval(script);
} catch (Throwable e) {
e.printStackTrace();
}
}
Get functions from script. I did not found other ways how to get all invokable methods from script except Reflection. Yeah, i know that this approach depends on ScriptEngine implementation, but it's the only one :)
public List getInvokableList() throws ScriptException {
List list = new ArrayList();
try {
Class compiledClass = compiledScript.getClass();
Field clasz = compiledClass.getDeclaredField("clasz");
clasz.setAccessible(true);
Class scrClass = (Class)clasz.get(compiledScript);
Method[] methods = scrClass.getDeclaredMethods();
clasz.setAccessible(false);
for (int i = 0, j = methods.length; i < j; i++) {
Annotation[] annotations = methods[i].getDeclaredAnnotations();
boolean ok = false;
for (int k = 0, m = annotations.length; k < m; k++) {
ok = annotations[k] instanceof CalculatedField;
if (ok) break;
}
if (ok)
list.add(methods[i].getName());
}
} catch (NoSuchFieldException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
}
return list;
}
In my task i don't need all functions, for this i create custom annotation and use it in the script:
#Retention(RetentionPolicy.RUNTIME)
#Target(ElementType.METHOD)
public #interface CalculatedField {
}
Script example:
import com.vssk.CalculatedField;
def utilFunc(s) {
s
}
#CalculatedField
def func3() {
utilFunc('Testing func from groovy')
}
Method to invoke script function by it's name:
public Object executeFunc(String name) throws Exception {
return ((Invocable)getEngine()).invokeFunction(name);
}

How to convert from JSObject to Map (viceversa) or list JSObject members

In Javascript i have the following code:
var r=applet.foo({var0:99,var1:'foo',var2:applet});
In my Java applet i have the following:
public JSObject foo(JSObject args){
System.out.println("The function is correctly invoked");
//In fact, the following works perfectly:
System.out.println("var1 is:"+(String)args.getMember("var1"));
JSObject w=JSObject.getWindow(this);
JSObject j=(JSObject)w.eval("new Object();");
Map m=new Hashmap();
//TODO here all the keys and values of args should be added to m
m.put("hello","world");
//TODO here all the keys and values of m should be added to j
return j;
}
How can this be done? (TODOs)
Reading http://docstore.mik.ua/orelly/web/jscript/ch19_06.html, i noticed theres a getSlot method for JSObject but if i do
args.getSlot(0)
all i have is one Exception:
netscape.javascript.JSException: No such slot 0 on JavaScript object
...

Unfortunately, Errandir's solution works only when you know a name of global variable that can be used to access an object you want to get properties' names of. You need to know this name to be able to add keys method to the object, and invoke it using JSObject's call method later. Of course, you can pass a global name of your object to Java if you have it. This solution doesn't look so good especially when you can't refer to your object in global context.
As an alternative, I proposed to use this of JSObject's eval method in the comment supposing that it will do all the work. And it does. But a big disappointent was that it works as expected only in Mozilla Firefox and Opera. In Internet Explorer 9 and Google Chrome (tested under Windows 7 and Ubuntu 12.04 LTS) this of eval method always refers to applet's document window ignoring which JavaScript object JSObject instance actually represents. I don't know whether it's a bug or simply LiveConnect is supported in these browsers very poorly.
The good news is that call method of JSObject executes specified function on the proper context. Keeping that in mind I finally found a solution how a list of names of JavaScript object's properties can be retrieved. The idea is to define a temporary function in global context using eval method. This function has to receive a JavaScript object we want to get properties of and to return names of these properties as an array. After that we can invoke the temporary function through JSObject's call method passing a Java representation of concerned JavaScript object (jsObject in my method below or args as it sounds in the question). At last, temporary function can be removed.
public static ArrayList<String> getJsObjectPropertiesNames(Applet applet, JSObject jsObject) {
if (applet == null || jsObject == null)
return null;
// Retrieving global context - a JSObject representing a window applet belongs to
JSObject globalContext;
try {
globalContext = JSObject.getWindow(applet);
}
catch (JSException ex) {
return null;
}
// Checking whether passed object is not an array
try {
jsObject.getSlot(0);
return null;
}
catch (JSException e) {
}
String keysFunctionName = String.format("_getKeys%d", Calendar.getInstance().getTimeInMillis());
jsObject.eval("window['" + keysFunctionName + "'] = function(jsObject) { return Object.keys(jsObject) }");
JSObject propertiesNamesJsObject = (JSObject)globalContext.call(keysFunctionName, new Object[] { jsObject });
jsObject.eval("delete(window['" + keysFunctionName + "'])");
ArrayList<String> propertiesNames = new ArrayList<>();
try {
int slotIndex = 0;
while (true) {
Object propertyName = propertiesNamesJsObject.getSlot(slotIndex);
if (propertyName instanceof String)
propertiesNames.add((String)propertyName);
slotIndex++;
}
}
catch (JSException e) {
}
return propertiesNames;
}

As a solution, you could define method keys as proposed here (You can do it within your java-code using JSObject.eval(...)). Then you could get keys like:
JSObject keys = (JSObject)args.call("keys", Collections.EMPTY_LIST);
keys.getSlot(0);

Here below I print a String, please modify it to get whatever you need.
public final static String getKeys = "{var keys = [];for (var key in this) {keys.push(key);} keys;}";
private static String printProperties(final Object o,
final boolean printType,
final int level,
final String tab) {
final StringBuilder sb = new StringBuilder(100);
if (printType) {
sb.append("(");
sb.append(o.getClass().getSimpleName());
sb.append(") ");
}
if (o instanceof JSObject) {
sb.append("{\n");
final JSObject js = (JSObject) o;
final JSObject keys = (JSObject) js.eval(getKeys);
boolean needComma = false;
for (int i = 0;; i++) {
final String key = (String) keys.getSlot(i);
if ((key != null) && !(key.equals("undefined"))) {
final Object val = js.getMember(key);
if (!needComma) {
needComma = true;
} else {
sb.append(",\n");
}
sb.append(multitab(tab, level));
sb.append(key);
sb.append(":");
sb.append(printProperties(val, printType, level + 1, tab));
} else {
break;
}
}
sb.append("\n");
sb.append(multitab(tab, level - 1));
sb.append("}");
} else {
sb.append(o);
}
return sb.toString();
}
private final static String tab = " ";
private static String multitab(final String tab,
int i) {
final StringBuilder sb = new StringBuilder();
while (i-- > 0) {
sb.append(tab);
}
return sb.toString();
}