= Chronicle Wire Chronicle Software :css-signature: demo :toc: macro :toclevels: 2 :icons: font
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== About
Chronicle Wire is a Wire Format abstraction library, The purpose of Chronicle Wire is to address the following concerns in a consistent manner:
== Design
Chronicle Wire uses Chronicle Bytes for bytes manipulation, and Chronicle Core for low level JVM access.
=== Why are these concerns conflated?
Often you want to use these interchangeably.
=== Features
Chronicle Wire supports a separation of describing what data you want to store and retrieve, and how it should be rendered/parsed. Chronicle Wire handles a variety of formatting options, for a wide range of formats.
A key aim of Chronicle Wire is to support schema changes. It should make reasonable attempts to handle:
bound data structure.Chronicle Wire will also be efficient where any, or all, of the following points are true:
Chronicle Wire is designed to make it easy to convert from one wire format to another. For example, you can use fixed-width binary data in memory for performance, and variable-width or text over the network. Different TCP connections could use different formats.
Chronicle Wire also supports hybrid wire formats. For example, you can have one format embedded in another.
== Support
This library requires Java 8. Support for C++ and C# is planned.
== Text Formats
The text formats include:
YAML - subset of mapping structures includedJSON - superset to support serializationCSV - superset to support serializationXML - plannedOptions include:
To support wire format discovery, the first byte should be in the ASCII range; adding an ASCII whitespace if needed.
== Binary Formats
The binary formats include:
Options for Binary format:
Note: Chronicle Wire supports debug/transparent combinations like self-describing data with zero copy support.
To support wire format discovery, the first bytes should have the top bit set.
== WireType Overview
|=============== |WireType |Enum |Human Readable |Self Describing |Size/ Latency |NOTE |TextWire |TEXT |YES |NO |More compact than JSON |YAML based |BinaryWire |BINARY |NO |YES |Better performance than YAML (half the latency) |Use this when only using Binary |BinaryWire |BINARY_LIGHT |NO |YES |Better performance than YAML (half the latency) |Use this when only using Binary, same as BINARY |BinaryWire |FIELDLESS_BINARY |NO |YES |Better performance than YAML (half the latency) | |JSONWire |JSON |YES |NO |Microsecond latencies |Uses a 4-bit length prefix |JSONWire |JSON_ONLY |YES |NO |Microsecond latencies |Uses new lines between messages |YamlWire |YAML |YES |NO |More compact than JSON |YAML based |YamlWire |YAML_ONLY |YES |NO |More compact than JSON |YAML based |RawWire |RAW |NO |YES |More compact than BinaryWire |Writes just the data without the metadata |CSVWire |CSV |YES |NO |More compact than JSON |YAML based |ReadAnyWire |READ_ANY |- |- |Can be either |Reads any format |===============
== Using Wire
=== link:https://github.com/OpenHFT/Chronicle-Wire/blob/ea/demo/src/main/java/run/chronicle/wire/demo/Example1.java[Simple use case]
First you need to have a buffer to write to.
This can be a byte[], a ByteBuffer, off-heap memory, or even an address and length that you have obtained from some other library.
Now you can choose which format you are using. As the wire formats are themselves unbuffered, you can use them with the same buffer, but in general using one wire format is easier.
So now you can write to the wire with a simple document.
wire.write("message").text("Hello World") .write("number").int64(1234567890L) .write("code").asEnum(TimeUnit.SECONDS) .write("price").float64(10.50);
prints
// The same code for BinaryWire wire2.write("message").text("Hello World") .write("number").int64(1234567890L) .write("code").asEnum(TimeUnit.SECONDS) .write("price").float64(10.50);
prints
Using RawWire strips away all the meta data to reduce the size of the message, and improves speed.
The down-side is that we cannot easily see what the message contains.
// The same code for RawWire wire3.write("message").text("Hello World") .write("number").int64(1234567890L) .write("code").asEnum(TimeUnit.SECONDS) .write("price").float64(10.50);
prints in RawWire.
//For more examples see https://github.com/OpenHFT/Chronicle-Wire/blob/master/README-Chapter1.md[Examples Chapter1] === link:https://github.com/OpenHFT/Chronicle-Wire/blob/ea/demo/src/main/java/run/chronicle/wire/demo/Example2.java[Simple example with a data type]
// Bytes which wraps a ByteBuffer which is resized as needed.
Bytes
Wire wire = new TextWire(bytes);
Data data = new Data("Hello World", 1234567890L, TimeUnit.NANOSECONDS, 10.50); data.writeMarshallable(wire); System.out.println(bytes);
prints
To write in binary instead
Bytes
data.writeMarshallable(wire2); System.out.println(bytes2.toHexString());
prints
00000000 c7 6d 65 73 73 61 67 65 eb 48 65 6c 6c 6f 20 57 ·message ·Hello W 00000010 6f 72 6c 64 c6 6e 75 6d 62 65 72 a6 d2 02 96 49 orld·num ber····I 00000020 c8 74 69 6d 65 55 6e 69 74 eb 4e 41 4e 4f 53 45 ·timeUni t·NANOSE 00000030 43 4f 4e 44 53 c5 70 72 69 63 65 90 00 00 28 41 CONDS·pr ice···(A
=== link:https://github.com/OpenHFT/Chronicle-Wire/blob/ea/demo/src/main/java/run/chronicle/wire/demo/Example3.java[Simple example with a nested data type]
In this example the data is marshalled as a nested data structure.
// Bytes which wraps a byte[] which is resized as needed Bytes<?> bytes = Bytes.allocateElasticOnHeap();
Wire wire = new TextWire(bytes);
Data data = new Data("Hello World", 1234567890L, TimeUnit.NANOSECONDS, 10.50); wire.write("mydata").marshallable(data); System.out.println(bytes);
prints
To write in binary instead
Bytes<?> bytes2 = new HexDumpBytes(); Wire wire2 = new BinaryWire(bytes2);
wire2.write("mydata").marshallable(data); System.out.println(bytes2.toHexString());
prints
c6 6d 79 64 61 74 61 # mydata 80 40 # Data c7 6d 65 73 73 61 67 65 # message eb 48 65 6c 6c 6f 20 57 6f 72 6c 64 # Hello World c6 6e 75 6d 62 65 72 # number a6 d2 02 96 49 # 1234567890 c8 74 69 6d 65 55 6e 69 74 # timeUnit eb 4e 41 4e 4f 53 45 43 4f 4e 44 53 # NANOSECONDS c5 70 72 69 63 65 90 00 00 28 41 # price
=== link:https://github.com/OpenHFT/Chronicle-Wire/blob/ea/demo/src/main/java/run/chronicle/wire/demo/Example4.java[Simple example with a data type with a type]
In this example, the type is encoded with the data. Instead of showing the entire package name which will almost certainly not work on any other platform, an alias for the type is used. It also means the message is shorter and faster.
Wire wire = new TextWire(Bytes.allocateElasticOnHeap());
ClassAliasPool.CLASS_ALIASES.addAlias(Data.class);
Data data = new Data("Hello World", 1234567890L, TimeUnit.NANOSECONDS, 10.50); wire.write("mydata").object(data); System.out.println(wire);
prints
To write in binary instead
Wire wire2 = new TextWire(Bytes.allocateElasticOnHeap());
wire2.write("mydata").object(data); System.out.println(wire2.bytes().toHexString());
prints
c6 6d 79 64 61 74 61 # mydata b6 04 44 61 74 61 # Data 80 40 # Data c7 6d 65 73 73 61 67 65 # message eb 48 65 6c 6c 6f 20 57 6f 72 6c 64 # Hello World c6 6e 75 6d 62 65 72 # number a6 d2 02 96 49 # 1234567890 c8 74 69 6d 65 55 6e 69 74 # timeUnit eb 4e 41 4e 4f 53 45 43 4f 4e 44 53 # NANOSECONDS c5 70 72 69 63 65 90 00 00 28 41 # price
=== link:https://github.com/OpenHFT/Chronicle-Wire/blob/ea/demo/src/main/java/run/chronicle/wire/demo/Example6.java[Write a message with a sequence of records]
// Bytes which wraps a ByteBuffer which is resized as needed
Bytes
Wire wire = new TextWire(bytes);
ClassAliasPool.CLASS_ALIASES.addAlias(Data.class);
Data[] data = { new Data("Hello World", 98765, TimeUnit.HOURS, 1.5), new Data("G'Day All", 1212121, TimeUnit.MINUTES, 12.34), new Data("Howyall", 1234567890L, TimeUnit.SECONDS, 1000) }; wire.writeDocument(false, w -> w.write("mydata") .sequence(v -> Stream.of(data).forEach(v::object)));
System.out.println(Wires.fromSizePrefixedBlobs(bytes));
List dataList = new ArrayList<>(); wire.readDocument(null, w -> w.read("mydata") .sequence(dataList, (l, v) -> { while (v.hasNextSequenceItem()) l.add(v.object(Data.class)); }));
prints
To write in binary instead
Bytes
wire2.writeDocument(false, w -> w.write("mydata") .sequence(v -> Stream.of(data).forEach(v::object))); System.out.println(Wires.fromSizePrefixedBlobs(bytes2));
List dataList2 = new ArrayList<>(); wire2.readDocument(null, w -> w.read("mydata") .sequence(dataList2, (l, v) -> { while (v.hasNextSequenceItem()) l.add(v.object(Data.class)); }));
prints
=== link:https://github.com/OpenHFT/Chronicle-Wire/blob/ea/demo/src/main/java/run/chronicle/wire/demo/Example7.java[Using the ClassAliasPool]
This example shows how to pass your classes to ClassAliasPool.CLASS_ALIASES.addAlias(Class<?>... classes), to create alias names for them so that you can refer to them without using the complete name of their packages.
// Create two classes Data1 and Data2 and add only the Data1.class to alias pool. static { ClassAliasPool.CLASS_ALIASES.addAlias(Data1.class); }
private static class Data1 extends SelfDescribingMarshallable { String name; int age; String address; }
private static class Data2 extends SelfDescribingMarshallable { String name; int age; String address; }
// Create instances of Data1 and Data2 Data1 data1 = new Data1(); data1.name = "James"; data1.age = 20; data1.address = "12 Kingston, London";
Printing out data1 and data2, you will see that the alias name is printed out for data1 but data2 appears with complete package name.
!Data1 { name: James, age: 20, address: "12 Kingston, London" }
Create configuration files cfg1.yaml and cfg2.yaml. See how the classes' names appear differently in yaml files for classes with alias name and without alias name. For Data1 object alias name is used in the yaml file (cfg1.yaml). Data2 object should be loaded from a yaml file with the complete name of class (including package name) otherwise you will receive an Exception.
You will see the complete package name for o2 object.
=== link:https://github.com/OpenHFT/Chronicle-Wire/blob/ea/demo/src/main/java/run/chronicle/wire/demo/Data.java[The code for the class Data]
class Data implements Marshallable { private String message; private long number; private TimeUnit timeUnit; private double price;
public Data() {
}
public Data(String message, long number, TimeUnit timeUnit, double price) {
this.message = message;
this.number = number;
this.timeUnit = timeUnit;
this.price = price;
}
public void setMessage(String message) {
this.message = message;
}
public void setNumber(long number) {
this.number = number;
}
public void setPrice(double price){
this.price =price;
}
public void setTimeUnit(TimeUnit timeUnit){
this.timeUnit = timeUnit;
}
public String getMessage() {
return message;
}
public long getNumber() {
return number;
}
public TimeUnit getTimeUnit() {
return timeUnit;
}
public double getPrice() {
return price;
}
@Override
public void readMarshallable(WireIn wire) throws IllegalStateException {
wire.read("message").text(this, Data::setMessage)
.read("number").int64(this, Data::setNumber)
.read("timeUnit").asEnum(TimeUnit.class, this, Data::setTimeUnit)
.read("price").float64(this,Data::setPrice);
}
@Override
public void writeMarshallable(WireOut wire) {
wire.write("message").text(message)
.write("number").int64(number)
.write("timeUnit").asEnum(timeUnit)
.write("price").float64(price);
}
@Override
public String toString() {
return "Data{" +
"message='" + message + '\'' +
", number=" + number +
", timeUnit=" + timeUnit +
", price=" + price +
'}';
}== A note on Wires.reset()
Chronicle Wire allows (and encourages) objects to be re-used in order to reduce allocation rates.
When a marshallable object is re-used or initialised by the framework, it is first reset by way of Marshallable.reset()
which is recommended over calling Wires.reset().
In the case of most DTOs with simple scalar values, this will not cause any issues.
However, more complicated objects with object instance fields may experience undesired behaviour.
In order to reset a marshallable object, the process is as follows:
Resettable interface, and the default value of the field is not null, and the current field value is of exactly the same class as the default value, value.reset() will be called. This behavior is introduced in Chronicle Wire 2.25.
b. when the field type is Collection or Map, and the default value is empty collection, it will be cleared.
c. there is specific built-in copy-by-value handling for some types such as Bytes
d. all other fields will be copied by reference from the new instance to the existing instanceThe object created in step 1 is cached for performance reasons, meaning that both the new and existing instance of the marshallable object could have a reference to the same object.
While this will not be a problem for primitive or immutable values (for example, int, Long, String), a mutable field such as ByteBuffer will cause problems.
Consider the following case:
public class BufferContainer { private final ByteBuffer b = ByteBuffer.allocate(16); }
The output of the test above is:
showing that the field b of each container object is now referencing the same ByteBuffer instance.
An exception to this is when the field value implements Resettable interface, when the default value of the field is not null, and the current field value is of exactly the same class as the default value. In this case, value.reset() will be called instead of overwriting it with default value by reference.
In order to work around this, if necessary, the marshallable class can override Marshallable.reset:
public class BufferContainer implements Marshallable { private ByteBuffer b = ByteBuffer.allocate(16);
@Override
public void reset() {
// or acquire from a pool if allocation should
// be kept to a minimum
b = ByteBuffer.allocate(16);
}If the field type implements Resettable (including Marshallable classes), and the field has non-null default value, the existing value will be reset without creating any extra garbage:
public class ComplexDto implements SelfDescribingMarshallable { private ContainedDto v = new ContainedDto(); // reset() will be propagated to this value }
== Binding to a field value
While serialized data can be updated by replacing a whole record, this might not be the most efficient option, nor thread-safe.
Chronicle Wire offers the ability to bind a reference to a fixed value of a field, and perform atomic operations on that field; for example, volatile read/write, and compare-and-swap.
// field to cache the location and object used to reference a field. private LongValue counter = null;
// find the field and bind an approritae wrapper for the wire format. wire.read(COUNTER).int64(counter, x -> counter = x);
Other types are supported; for example, 32-bit integer values, and an array of 64-bit integer values.
== Pass-by-name or Dynamic Enums
Chronicle Wire supports passing objects reference by the name() of the object referenced.
This is supported trivially with enum which define a name() for you. e.g.
enum ServerId { LN_A }
interface Output { void serverId(ServerId serverId); }
// later Output out; // is a MethodWriter
.Message on the Wire [source,yaml] serverId: LN_A
However, we might wish to alter metadata associated with the enum
enum ServerId implements DynamicEnum { LN_A(101);
public int priority;=== Not passing by name
Sometimes you need to pass the actually data, esp the first time. This can be achieved by using the @AsMarshallable annotation which will always pass the object as a typedMarshallable.
public class RefData extends AbstractEventCfg
public RefData(DynamicEnum data) {
this.data = data;
}
public DynamicEnum data() {
return data;
}You can choose to update the existing enum with this information.
NOTE: You can add an enum which didn't exist.
NOTE: You can't use an enum before it is defined, this is assumed to be in input error.
=== Pass by reference
You may wish to pass by reference a data type which is not an enum.
This can be done by adding DynamicEnum to a regular class and adding a name field.
class MyData implements DynamicEnum { public static final MyData ONE = new MyData("One"); // used as a predefined object public static final MyData TWO = new MyData("Two"); // used as a predefined object private String name; // set via reflection.
@Override public String name() { return name; }NOTE: This is particularly useful if you have a class which must extend another parent.
The consumer doesn't need to do anything special to use the new enum, however the producer need to create it in code as follows.
ServerId serverId = EnumCache.of(ServerId.class).nameFor("HK_A"); serverId.priority(200); out.refData(new RefData(serverId));
NOTE: The unique key for these objects is their type and name. Two objects of different types can have the same name.
IMPORTANT: These objects passed by reference are never cleaned up. Only use them when there is likely to be a limited number of them over the life of the application.
== Using @MethodId
You can assign a method id to a method using the annotation @MethodId(long int: id).
The provided id should be unique across all classes using the same MethodReader/Writer, therefore it is safe practice to use unique method id in your entire system.A method name can be determined from its method id and this results in saving memory when calling the method.The following example shows the difference between memory usage when using method id and when not using it.In this example the method saysomethingnice() has been annotated with MethodId(7) and it has been called from shouldDetermineMethodNamesFromMethodIds().
interface Speaker { @MethodId(7) void saysomethingnice(final String message); }
void shouldDetermineMethodNamesFromMethodIds() { Bytes<?> bytes = Bytes.allocateElasticOnHeap();
final BinaryWire wire = new BinaryWire(bytes);
final Speaker speaker =
wire.methodWriterBuilder(Speaker.class).get();
speaker.saysomethingnice("hello");== Bytes options
Chronicle Wire is built on top of the Bytes library, however Bytes, in turn, can wrap:
ByteBuffer - heap and directbyte[] - using ByteBufferbyte[] or primitive array without ByteBuffer== Handling instance classes of an unknown type
This feature allows Chronicle Wire to de-serialize, manipulate, and serialize an instance class of an unknown type.
If the type is unknown at runtime, a proxy is created; assuming that the required type is an interface.
When the tuple is serialized, it will be give the same type as when it was deserialized, even if that class is not available.
Methods following our getter/setter convention will be treated as getters and setters.
This feature is needed for a service that stores and passes on data, for classes it might not have in its class path.
NOTE: This is not garbage collection free, but if the volume is low, this may be easier to work with.
NOTE: This only works when the expected type is not a class.
=== LongConversionExample
@Test public void unknownType() throws NoSuchFieldException { Marshallable marshallable = Wires.tupleFor(Marshallable.class, "UnknownType"); marshallable.setField("one", 1); marshallable.setField("two", 2.2); marshallable.setField("three", "three"); String toString = marshallable.toString(); assertEquals("!UnknownType {\n" + " one: !int 1,\n" + " two: 2.2,\n" + " three: three\n" + "}\n", toString); Object o = Marshallable.fromString(toString); assertEquals(toString, o.toString()); }
@Test public void unknownType2() { String text = "!FourValues {\n" + " string: Hello,\n" + " num: 123,\n" + " big: 1e6,\n" + " also: extra\n" + "}\n"; ThreeValues tv = Marshallable.fromString(ThreeValues.class, text); assertEquals(text, tv.toString()); assertEquals("Hello", tv.string()); tv.string("Hello World"); assertEquals("Hello World", tv.string());
assertEquals(123, tv.num());
tv.num(1234);
assertEquals(1234, tv.num());
assertEquals(1e6, tv.big(), 0.0);
tv.big(0.128);
assertEquals(0.128, tv.big(), 0.0);
assertEquals("!FourValues {\n" +
" string: Hello World,\n" +
" num: !int 1234,\n" +
" big: 0.128,\n" +
" also: extra\n" +
"}\n", tv.toString());}
interface ThreeValues { ThreeValues string(String s); String string();
ThreeValues num(int n);
int num();
ThreeValues big(double d);
double big();== Handling unexpected fields
By default, Chronicle Wire skips fields which names don't match any field of the DTO class. It's possible to capture such fields by overriding method or ReadMarshallable:
default void unexpectedField(Object event, ValueIn valueIn) {
valueIn.skipValue();
}One of best practices is saving unexpected fields in order to process them after the deserialization:
transient Map<String, Object> others = new LinkedHashMap<>();
@Override
public void unexpectedField(Object event, ValueIn valueIn) {
others.put(event.toString(), valueIn.object());
}It's also possible to use fail-fast approach and throw an exception:
@Override
public void unexpectedField(Object event, ValueIn valueIn) {
throw new IllegalStateException("Unexpected field: name=" + event + ", value=" + valueIn);
}Exceptions that are thrown from this method are never swallowed, they are wrapped into runtime UnexpectedFieldHandlingException and thrown back to a high-level API call.
== LongConversionExample with MethodReaders
@Test public void testUnknownClass() { Wire wire2 = new TextWire(Bytes.elasticHeapByteBuffer(256)); MRTListener writer2 = wire2.methodWriter(MRTListener.class);
String text = "top: !UnknownClass {\n" +
" one: 1,\n" +
" two: 2.2,\n" +
" three: words\n" +
"}\n" +
"---\n" +
"top: {\n" +
" one: 11,\n" +
" two: 22.2,\n" +
" three: many words\n" +
"}\n" +
"---\n";
Wire wire = TextWire.from(text);
MethodReader reader = wire.methodReader(writer2);
assertTrue(reader.readOne());
assertTrue(reader.readOne());
assertFalse(reader.readOne());
assertEquals(text, wire2.toString());=== Filtering with MethodReaders
To support filtering, you need to make sure the first of multiple arguments can be used to filter the method call. If you have only one argument, you may need to add an additional argument to support efficient filtering.
This feature calls an implementation of MethodFilterOnFirstArg to see if the rest of the method call should be parsed.
For example, today you have:
This can be migrated to:
where the implementation can look like this:
class MyInterfaceImpl extends MyInterface { public void method(ExpensiveDto dto) { // something }
public void method2(String filter, ExpensiveDto dto) {
method(dto);
}
public boolean ignoreMethodBasedOnFirstArg(String methodName, String filter) {
return someConditionOn(methodName, filter);
}For an example, see net.openhft.chronicle.wire.MethodFilterOnFirstArgTest.
=== Intercepting MethodReader calls
You may wish to intercept handling a call in the method reader in order to execute additional logic, to record a call somewhere for monitoring purposes, or to even skip the original method invocation.
==== Intercepting by passing control over the original method call
MethodReader provides a flexible feature for supporting all the above use cases -- the option to specify MethodReaderInterceptorReturns.
If set, it will be triggered instead of the original call. It's possible to either skip the original method or to call it via passed Invocation instance:
==== Intercepting by modifying MethodReader generated source code
GeneratingMethodReaderInterceptorReturns allows to change the logic of MethodReader without an overhead provided by reflexive calls.
Code returned by codeBeforeCall and codeAfterCall will be added before and after actual method call in the generated source code of the method reader. It's possible to use original call arguments and object instance in the added code.
Simple example that enforces skipping the original call in case the second agrument is null:
class SkippingInterceptor implements GeneratingMethodReaderInterceptorReturns { @Override public String generatorId() { return "skipping"; }
@Override
public String codeBeforeCall(Method m, String objectName, String[] argumentNames) {
return "if (" + argumentNames[1] + " != null) {";
}
@Override
public String codeAfterCall(Method m, String objectName, String[] argumentNames) {
return "}";
}If the code provided by generating interceptor differs from the code provided by another generating interceptor, their generatorId should be different as well. It's needed to ensure re-compilation in case a new interceptor is passed.
See MethodReaderInterceptorReturnsTest for more examples.
=== Spring Boot and dynamic compilation in Chronicle Wire
Chronicle Wire's MethodReader and MethodWriter dynamically compile Java code to get around some limitations in Java's underlying proxy mechanism and to do this the Java platform's standard compilation mechanism is used. The platform compiler uses the classpath variable to look for classes in directories and JAR files, and is not able to make use of classloaders to find classes.
Spring Boot uses a custom deployment mechanism - all classes and JARs are deployed in a fat JAR and Spring's classloader can extract classes from this. In order for the compiler to be able to see classes from the fat JAR, the classes should be extracted onto the disk somewhere. This is easy if the classes are contained in a JAR (i.e. a JAR inside the fat JAR) - Spring can be made to extract the JAR to a temp directory, such as by configuring Maven Spring Boot plugin:
This will allow the latest Chronicle-Wire to use classes in those JAR files.
Dynamic compilation may be also configured via Gradle Spring Boot plugin:
NOTE: For more information see link:https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#howto.build.extract-specific-libraries-when-an-executable-jar-runs[Extract Specific Libraries When an Executable JAR Runs] and link:https://docs.spring.io/spring-boot/docs/current/gradle-plugin/reference/html/#packaging-executable-configuring-unpacking[Spring Boot Gradle Plugin Reference Guide].
== Using MethodWriter and MethodReader
Chronicle Wire's MethodWriter is used for writing data, and MethodReader is used for then reading this data. However,
there are many use cases for them. One of many benefits to these are their ease of use.
In particular, link:https://vanilla-java.github.io/2016/03/23/Microservices-in-the-Chronicle-world-Part-1.html[this article] captures the simplicity of using MethodWriter and MethodReader.
In another example, link:https://dzone.com/articles/java-how-to-leverage-method-chaining-to-add-smart[here], we can see how written data could be sent as a streaming event over an Event-Driven architecture, and then a MethodReader could be used to read these streaming events.
These are also not limited to being used only within Chronicle Wire. With Chronicle Queue for instance, another example would be to have a MethodWriter that serialises and writes a method call to the out queue,
and a MethodReader that reads in the in queue for any methods implemented. For more detail about this example, see link:https://github.com/OpenHFT/Chronicle-Queue-Demo/blob/c1e128545e8f219daa186836ca58a07047436084/md-pipeline/src/main/java/org/trading/Runner.java[here].
== Uses of Chronicle Wire
Chronicle Wire can be used for:
== Similar projects
=== Simple Binary Encoding (SBE)
Simple Binary Encoding (SBE) is designed to be a more efficient replacement for FIX. It is not limited to FIX protocols, and can be easily extended by updating an XML schema. It is simple, binary, and it supports C++ and Java.
XML, when it first started, did not use XML for its own schema files, and it is not insignificant that SBE does not use SBE for its schema either. This is because it is not trying to be human-readable. It has XML which, though standard, is not designed to be human-readable either. Chronicle believes that it is a limitation that it does not naturally lend itself to a human-readable form.
The encoding that SBE uses is similar to binary; with field numbers and fixed-width types.
SBE assumes the field types, which can be more compact than Chronicle Wire's most similar option; though not as compact as others.
SBE has support for schema changes provided that the type of a field doesn't change.
=== Message Pack (msgpack)
Message Pack is a packed binary wire format which also supports JSON for human readability and compatibility.
It has many similarities to the binary (and JSON) formats of this library.
Chronicle Wire is designed to be human-readable first, based on YAML, and has a range of options to make it more efficient.
The most extreme being fixed position binary.
Message Pack has support for embedded binary, whereas Chronicle Wire has support for comments and hints, to improve rendering for human consumption.
The documentation looks well-thought-out, and it is worth emulating.
=== Comparison with Cap'n'Proto
|=============== | Feature | Wire Text | Wire Binary | Protobuf | Cap'n Proto | SBE | FlatBuffers | Schema evolution | yes | yes | yes | yes | caveats | yes | Zero-copy | yes | yes | no | yes | yes | yes | Random-access reads | yes | yes | no | yes | no | yes | Random-access writes | yes | yes | no | ? | no | ? | Safe against malicious input | yes | yes | yes | yes | yes | opt-in / upfront | Reflection / generic algorithms | yes | yes | yes | yes | yes | yes | Initialization order | any | any | any | any | preorder | bottom-up | Unknown field retention | yes | yes | yes | yes | no | no | Object-capability RPC system | yes | yes | no | yes | no | no | Schema language | no | no | custom | custom | XML | custom | Usable as mutable state | yes | yes | yes | no | no | no | Padding takes space on wire? | optional | optional | no | optional | yes | yes | Unset fields take space on wire? | optional | optional | no | yes | yes | no | Pointers take space on wire? | no | no | no | yes | no | yes | Pass-by-name (Dynamic Enums) | yes | no | no | no | no | no | C++ | yes | planned | yes | yes (C++11) | yes | yes | Java | Java 8 | Java 8 | yes | yes | yes | yes | C# | yes | yes | yes | yes | yes | yes | Go | no | no | yes | yes | no | yes | Other languages | no | no | 6+ | others | no | no | Authors' preferred use case | distributed computing | financial / trading | distributed computing | platforms / sandboxing | financial / trading | games |===============
NOTE: The Binary YAML format can be automatically converted to YAML without any knowledge of the schema, because the messages are self-describing.
NOTE: You can parse all the expected fields (if any) and then parse any remaining fields.
As YAML supports object field names (or keys), these could be strings or even objects as keys and values.
Based on https://capnproto.org/news/2014-06-17-capnproto-flatbuffers-sbe.html
NOTE: It is not clear what padding which does not take up space on the wire means.
== Design notes
See https://capnproto.org/news/2014-06-17-capnproto-flatbuffers-sbe.html for a comparison to other encoders.
=== Schema evolution
Wire optionally supports:
The more flexibility, the larger the overhead in terms of CPU and memory. Chronicle Wire allows you to dynamically pick the optimal configuration, and convert between these options.
=== Zero copy
Chronicle Wire supports zero-copy random access to fields, and direct-copy from in-memory to the network. It also supports translation from one wire format to another. For example, switching between fixed-length data and variable-length data.
=== Random Access
You can access a random field in memory, For example, in a 2TB file, page-in/pull-into CPU cache, only the data relating to your read or write.
[options="header"] |=============== | format | access style | fixed-length binary | random access without parsing first | variable-length binary | random access with partial parsing allowing you to skip large portions | fixed-length text | random access with parsing | variable-length text | no random access |===============
Chronicle Wire references are relative to the start of the data contained, to allow loading in an arbitrary point in memory.
=== Safe against malicious input
Chronicle Wire has built in tiers of bounds checks to prevent accidental read/writing that corrupts the data. It is not complete enough for a security review.
=== Reflection / generic algorithms
Chronicle Wire supports generic reading and writing of an arbitrary stream.
This can be used in combination with predetermined fields.
For example, you can read the fields you know about, and ask it to provide the fields that you do not.
You can also give generic field names like keys to a map as YAML does.
=== Initialization order
Chronicle Wire can handle unknown information like lengths, by using padding. It will go back and fill in any data that it was not aware of when it was writing the data. For example, when it writes an object, it does not know how long it is going to be, so it adds padding at the start. Once the object has been written, it goes back and overwrites the length. It can also handle situations where the length was more than needed; this is known as packing.
=== Unknown field retention
Chronicle Wire can read data that it did not expect, interspersed with data it did expect.
Rather than specify the expected field name, a StringBuilder is provided.
NOTE: There are times when you want to skip/copy an entire field or message, without reading any more of it. This is also supported.
=== Object-maximumLimit RPC system
Chronicle Wire supports references based on name, number, or UUID. This is useful when including a reference to an object that the reader should look up by other means.
A common case is if you have a proxy to a remote object, and you want to pass or return this in an RPC call.
=== Schema language
Chronicle Wire's schema is not externalised from the code.
However, it is planned to use YAML in a format that it can parse.
=== Usable as mutable state
Chronicle Wire supports storing an application's internal state. This will not allow it to grow or shrink. You can't free any of it without copying the pieces that you need, and discarding the original copy.
=== Padding takes space on the wire
The Chronicle Wire format that is chosen determines if there is any padding on the wire. If you copy the in-memory data directly, its format does not change.
If you want to drop padding, you can copy the message to a wire format without padding. You can decide whether the original padding is to be preserved or not, if turned back into a format with padding.
We could look at supporting Cap'n'Proto's zero-byte removal compression.
=== Un-set fields take space on the wire
Chronicle Wire supports fields with, and without, optional fields, and automatic means of removing them. Chronicle Wire does not support automatically adding them back in, because information has been lost.
=== Pointers take space on the wire
Chronicle Wire does not have pointers, but it does have content-lengths which are a useful hint for random access and robustness; but these are optional.
== Working with IntelliJ
These templates can be added to IntelliJ to create simple getters and setters.
== Why use Marshallable objects
Marshallable objects have been designed to allow you to
toString(), hashCode() and equals(Object) methods created for you.== Pojo LongConversionExample The following is a simple example of a POJO with a nested data type in a List.
import net.openhft.chronicle.wire.SelfDescribingMarshallable;
class MyPojo extends SelfDescribingMarshallable { String text; int num; double factor;
public MyPojo(String text, int num, double factor) {
this.text = text;
this.num = num;
this.factor = factor;
}}
class MyPojos extends SelfDescribingMarshallable {
String name;
List
public MyPojos(String name) {
this.name = name;
}By extending SelfDescribingMarshallable the class has an implementation
for readMarshallable(WireIn), writeMarshallable(WireOut) and from these
toString(), hashCode() and equals(Object). You only need to define the method
yourself for improved efficiency. These default implementations can give you
2/3rds of the performance of hand coding but save time and potential errors
writing them yourself.
=== The toString()
An important feature of the toString() method is no information is lost.
The object can be reconstructed from the output of the toString() method.
This is useful for building sample data in unit tests for from a file.
It also means that you can take the dump of an object in a log file and reconstruct the original object.
MyPojos mps = new MyPojos("test-list"); mps.myPojos.add(new MyPojo("text1", 1, 1.1)); mps.myPojos.add(new MyPojo("text2", 2, 2.2));