I am moving from C++ to Java, and I am used to the way boost serialization works for xml. What is very good with it is:
that I only have to write one function that is used for both parsing and generating the XML. This function is basically a mapping between the field value and the name of the xml tag.
that the XML generated is light weight, and only contain the information we want to save (no information about the type of the field, the name of the class...)
I am looking for something that would have the same advantages, in JAVA. Here is a C++ example:
struct ContractDefinition
: public fme::ToStringInterface
{
public:
std::string name;
template<class archive>
void serialize(archive& ar, const unsigned int FME_UNUSED(version))
{
using boost::serialization::make_nvp;
ar & make_nvp< std::string >("name", name);
}
};
and the result looks like that:
<name>WHATEVER THE NAME IS</name>
Take a look at jaxb.
Related
I want to use a single YAML file which contains several different objects - for different applications. I need to fetch one object to get an instance of MyClass1, ignoring the rest of docs for MyClass2, MyClass3, etc. Some sort of selective de-serializing: now this class, then that one... The structure of MyClass2, MyClass3 is totally unknown to the application working with MyClass1. The file is always a valid YAML, of course.
The YAML may be of any structure we need to implement such a multi-class container. The preferred parsing tool is snakeyaml.
Is it sensible? How can I ignore all but one object?
UPD: replaced all "document" with "object". I think we have to speak about the single YAML document containing several objects of different structure. More of it, the parser knows exactly only 1 structure and wants to ignore the rest.
UDP2: I think it is impossible with snakeyaml. We have to read all objects anyway - and select the needed one later. But maybe I'm wrong.
UPD2: sample config file
---
-
exportConfiguration781:
attachmentFieldName: "name"
baseSftpInboxPath: /home/user/somedir/
somebool: false
days: 9999
expected:
- ABC w/o quotes
- "Cat ABC"
- "Some string"
dateFormat: yyyy-MMdd-HHmm
user: someuser
-
anotherConfiguration:
k1: v1
k2:
- v21
- v22
This is definitely possible with SnakeYAML, albeit not trivial. Here's a general rundown what you need to do:
First, let's have a look what loading with SnakeYAML does. Here's the important part of the YAML class:
private Object loadFromReader(StreamReader sreader, Class<?> type) {
Composer composer = new Composer(new ParserImpl(sreader), resolver, loadingConfig);
constructor.setComposer(composer);
return constructor.getSingleData(type);
}
The composer parses YAML input into Nodes. To do that, it doesn't need any knowledge about the structure of your classes, since every node is either a ScalarNode, a SequenceNode or a MappingNode and they just represent the YAML structure.
The constructor takes a root node generated by the composer and generates native POJOs from it. So what you want to do is to throw away parts of the node graph before they reach the constructor.
The easiest way to do that is probably to derive from Composer and override two methods like this:
public class MyComposer extends Composer {
private final int objIndex;
public MyComposer(Parser parser, Resolver resolver, int objIndex) {
super(parser, resolver);
this.objIndex = objIndex;
}
public MyComposer(Parser parser, Resolver resolver, LoaderOptions loadingConfig, int objIndex) {
super(parser, resolver, loadingConfig);
this.objIndex = objIndex;
}
#Override
public Node getNode() {
return strip(super.getNode());
}
private Node strip(Node input) {
return ((SequenceNode)input).getValue().get(objIndex);
}
}
The strip implementation is just an example. In this case, I assumed your YAML looks like this (object content is arbitrary):
- {first: obj}
- {second: obj}
- {third: obj}
And you simply select the object you actually want to deserialize by its index in the sequence. But you can also have something more complex like a searching algorithm.
Now that you have your own composer, you can do
Constructor constructor = new Constructor();
// assuming we want to get the object at index 1 (i.e. second object)
Composer composer = new MyComposer(new ParserImpl(sreader), new Resolver(), 1);
constructor.setComposer(composer);
MyObject result = (MyObject)constructor.getSingleData(MyObject.class);
The answer of #flyx was very helpful for me, opening the way to workaround the library (in our case - snakeyaml) limitations by overriding some methods. Thanks a lot! It's quite possible there is a final solution in it - but not now. Besides, the simple solution below is robust and should be considered even if we'd found the complete library-intruding solution.
I've decided to solve the task by double distilling, sorry, processing the configuration file. Imagine the latter consisting of several parts and every part is marked by the unique token-delimiter. For the sake of keeping the YAML-likenes, it may be
---
#this is a unique key for the configuration A
<some YAML document>
---
#this is another key for the configuration B
<some YAML document
The first pass is pre-processing. For the given String fileString and String key (and DELIMITER = "\n---\n". for example) we select a substring with the key-defined configuration:
int begIndex;
do {
begIndex= fileString.indexOf(DELIMITER);
if (begIndex == -1) {
break;
}
if (fileString.startsWith(DELIMITER + key, begIndex)) {
fileString = fileString.substring(begIndex + DELIMITER.length() + key.length());
break;
}
// spoil alien delimiter and repeat search
fileString = fileString.replaceFirst(DELIMITER, " ");
} while (true);
int endIndex = fileString.indexOf(DELIMITER);
if (endIndex != -1) {
fileString = fileString.substring(0, endIndex);
}
Now we feed the fileString to the simple YAML parsing
ExportConfiguration configuration = new Yaml(new Constructor(ExportConfiguration.class))
.loadAs(fileString, ExportConfiguration.class);
This time we have a single document that must co-respond to the ExportConfiguration class.
Note 1: The structure and even the very content of the rest of configuration file plays absolutely no role. This was the main idea, to get independent configurations in a single file
Note 2: the rest of configurations may be JSON or XML or whatever. We have a method-preprocessor that returns a String configuration - and the next processor parses it properly.
i am stucked on something : i have some .idl files that generates java classes from structs defined in those files like this :
struct MapServiceLayer{
string id;
string name;
string parentId;
OsTypes::StringSeq childrenIds;
};
However I need to have a JAVA class where one of it's Attributes needs to be of type Java.Object because when i will instantiate this class, its attribute could be of different type. So i tried this :
struct MapServiceFeatureAttribute{
OsTypes::ObjectSeq value;
};
and this :
struct MapServiceFeatureAttribute{
OsTypes::AnySeq value;
};
But none of those worked.
I also have heard about Unions but i am definitely not sure about how to use them. If someone knows how to get a Java.Object from idls this would be Great. If it's not possible maybe someone knows how to do with unions !
thanks in advance.
After some more deep research it seems that it is not possible to get a java.lang.object. However you can have a behavior that could do the trick using Any corba object :
After having generated your sources you will have a class with an attribute of type Any, this type allows you to store different types in it by using :
Any anyObj;
anyObj.insert_string(String s);
anyObj.insert_long(long l);
anyObj.insert_double(double d);
and you can obviously get the value and the chosen type by using :
String s1 = anyObj.extract_string(String s);
long l1 = anyObj.extract_long(long l);
double d1 = anyObj.extract_double(double d);
i gave the exemple for those 3 types but there is several more.
In my case, there might be different data type of same json field. Example:
"need_exp":1500
or
"need_exp":"-"
How to process this case? I know it can be processed by parse or use custom encoders, but this is a very complex json text, is there any way to solve that without rewriting the whole decoder (for example, just "tell" the decoder to convert all Int to String in need_exp field)?
It is called a disjunction which can be encoded with the Scala standard Either class.
Simply map the json that to the following class:
case class Foo(need_exp: Either[String, Int])
My solution is to use a custom decoder. Rewrite a little part of the JSON can be fine.
For example, there is a simple JSON:
{
/*many fields*/
"hotList":[/* ... many lists inside*/],
"list":[ {/*... many fields*/
"level_info":{
"current_exp":11463,
"current_level":5,
"current_min":10800,
"next_exp":28800 //there is the problem
},
"sex":"\u4fdd\u5bc6"},/*...many lists*/]
}
In this case, I don't need to rewrite the whole JSON encoder, just write a custom encoder of level_info:
implicit val decodeUserLevel: Decoder[UserLevel] = (c: HCursor) => for
{
current_exp <- c.downField("current_exp").as[Int]
current_level <- c.downField("current_level").as[Int]
current_min <- c.downField("current_min").as[Int]
next_exp <- c.downField("next_exp").withFocus(_.mapString
{
case """-""" => "-1"
case default => default
}).as[Int]
} yield
{
UserLevel(current_exp, current_level, current_min, next_exp)
}
and it worked.
I have a model which is in XML format as shown below and I need to parse the XML and check whether my XML has internal-flag flag set as true or not. In my other models, it might be possible, that internal-flag flag is set as false. And sometimes, it is also possible that this field won't be there so by default it will be false from my code.
<?xml version="1.0"?>
<ClientMetadata
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.google.com client.xsd"
xmlns="http://www.google.com">
<client id="200" version="13">
<name>hello world</name>
<description>hello hello</description>
<organization>TESTER</organization>
<author>david</author>
<internal-flag>true</internal-flag>
<clock>
<clock>
<for>
<init>val(tmp1) = 1</init>
<clock>
<eval><![CDATA[result("," + $convert(val(tmp1)))]]></eval>
</clock>
</for>
<for>
<incr>val(tmp1) -= 1</incr>
<clock>
<eval><![CDATA[result("," + $convert(val(tmp1)))]]></eval>
</clock>
</for>
</clock>
</clock>
</client>
</ClientMetadata>
I have a POJO in which I am storing my above model -
public class ModelMetadata {
private int modelId;
private String modelValue; // this string will have my above XML data as string
// setters and getters here
}
Now what is the best way to determine whether my model has internal-flag set as true or not?
// this list will have all my Models stored
List<ModelMetadata> metadata = getModelMetadata();
for (ModelMetadata model : metadata) {
// my model will be stored in below variable in XML format
String modelValue = model.getModelValue();
// now parse modelValue variable and extract `internal-flag` field property
}
Do I need to use XML parsing for this or is there any better way to do this?
Update:-
I have started using Stax and this is what I have tried so far but not sure how can I extract that field -
InputStream is = new ByteArrayInputStream(modelValue.getBytes());
XMLStreamReader r = XMLInputFactory.newInstance().createXMLStreamReader(is);
while(r.hasNext()) {
// now what should I do here?
}
There is an easy solution using XMLBeam (Disclosure: I'm affiliated with that project), just a few lines:
public class ReadBoolean {
public interface ClientMetaData {
#XBRead("//xbdefaultns:internal-flag")
boolean hasFlag();
}
public static void main(String[] args) throws IOException {
ClientMetaData clientMetaData = new XBProjector().io().url("res://xmlWithBoolean.xml").read(ClientMetaData.class);
System.out.println("Has flag:"+clientMetaData.hasFlag());
}
}
This program prints out
Has flag:true
for your XML.
You could also do some simple string parsing, but this will only work for small cases with proper XML and if there's only a single <internal-flag> element.
This is a simple solution to your problem without using any XML parsing utilities. Other solutions may be more robust or powerful.
Find the index of the string literal <internal-flag>. If it doesn't exist, return false.
Go forward "<internal-flag>".length (15) characters. Read up to the next </internal-flag>, which should be the string true or false.
Take that string, use Boolean.parseBoolean(String) to get a boolean value.
If you want me to help you out with the code just drop a comment!
If you are willing to consider adding Groovy to your mix (e.g. see the book Making Java Groovy) then using a Groovy XMLParser and associated classes will make this simple.
If you need to stick to Java, let me put in a shameless plug for my Xen library, which mimics a lot of the "Groovy way". The answer to your question would be:
Xen doc = new XenParser().parseText(YOUR_XML_STRING);
String internalFlag = doc.getText(".client.internal-flag");
boolean isSet = "true".equals(internalFlag);
If the XML comes from a File, Stream, or URI, that can be handled too.
Caveat emptor, (even though it is free) this is a fairly new library, written solely by a random person (me), and not thoroughly tested on all the crazy XML out there. If anybody knows of a similar, more "mainstream" library I'd be very interested in hearing about it.
Whilest learning Python 3 and converting some of my code from Java to Python 3.3 I came across a small problem I haven't been able to fix.
In Java I have this code (just dummy code to make it smaller):
public enum Mapping {
C11{public int getMapping(){ return 1;}},
C12{public int getMapping(){ return 2;}},
public abstract int getMapping();
}
String s = "C11";
System.out.println(Mapping.valueOf(s))
Works fine and prints the requisted '1'
Trying to do this in Python doesn't work that easy (yet). I tried to imitate an Enum with:
class Mapping:
C11=1
C12=2
s = 'C11'
print(Mapping.Mapping.(magic should happen here).s)
Unfortunately I have no idea how to convert a string to an attribute to be called like that (or something similar).
I need this because I have a HUGE list in the class Mapping and need to convert seemingly random words read from a text file to an integer mapping.
You are looking for getattr:
>>> getattr(Mapping, s)
1
From the documentation:
getattr(object, name[, default])
Return the value of the named attribute of object. name must be a string. If the string is the name of one of the object’s attributes, the result is the value of that attribute. For example, getattr(x, 'foobar') is equivalent to x.foobar. If the named attribute does not exist, default is returned if provided, otherwise AttributeError is raised.
Use getattr:
class Mapping:
C11=1
C12=2
print(getattr(Mapping, 'C11')) # prints 1