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JavaPath-Skriptsprache für den Zugriff auf komplexe Datenstrukturen

Der Artikel beschreibt die deklarative Skriptsprache JavaPath als Alternative zur Verwendung von Java Reflection und eine Möglichkeit, die "Service-Hölle" in eigenständigen Anwendungen mit komplexen Datenstrukturen zu vermeiden.


Beschreibung des Problems


Betrachten Sie eine tief verschachtelte Struktur


class A{
   B b;
}
class B{
   C c;
}
class C{
   String name;
}

Wenn wir dem Namensfeld der Klasse C einen Wert zuweisen müssen, ohne direkten Zugriff auf Instanz A zu haben, hilft eine Zwischenschicht der Service-API.


private A a;
public void setNameService(String name) {
    a.b.c.name = name;
}

, , . , .


private A a;
public void setNameService(String name) {
    if(a == null) {
        a = new A();
    }
    if(a.b == null) {
        a.b = new B();
    }
    if(a.b.c == null) {
        a.b.c = new C();
    }
    a.b.c.name = name;
}

, , setNameService(String name) , , a, b c, , .


API, , , API. . , . , , 'C' name, 'B' 'A' .


, - . , , , . - - . , . , , , , .


JavaPath , .


JavaPath


JavaPath.


private A a = new A();
private final JavaPath javaPath = new JavaPath(A.class);

public void setNameService(String name) {
    javaPath.evalPath("b.c.name", a, name);
}

setNameService.


, JavaPath — , Java. JavaPath . , . JavaPath . -public. . JavaPath private final .


: — JavaPath!


final String str = "VALUE";
JavaPath javaPath = new JavaPath(String.class);
assertEquals("VALUE",str);
//  private final byte[] value;  String 
javaPath.evalPath("value",str,"THE HACK".getBytes());
assertEquals("THE HACK",str);

- , , JavaPath Java Reflection .


, JavaPath . . .


JavaPath


public Object evalPath(String path, Object root, Object... values);

evalPath


  • — Java
  • A — b
  • , . — — name

, . C. .


class C{
    String name;
    public void setName(String name) {
        this.name = name;
    }   
}

. .


A a = new A();
JavaPath javaPath = new JavaPath(A.class);
public void setNameService(String name) {
    javaPath.evalPath("b.c.setName", a, name);
}

JavaPath , , , :


    javaPath.evalPath("b.c.setName($)", a, name);

$ $0 — .



a0.a1.… .an



a0.a1.… .an-1


, , / null. an . , , , evalPath. , . JavaPath .


JavaPath


JavaPath , . . . , , , . , , ,
Java . , , , API.



Syntaxdiagramm



JavaPath . . , , , . . , , , .. — .


$ #


Spezielle Parameter



, evalPath $[:digit:]* . $ , . .


.


JavaPath
"a($)",
"a($0)"
"a($1.name)"name,


. : #[:digit:]* # #0


.


JavaPath
"a(#)"
"a(#0.name)"name
"a.b(#1)"'a'

, -.


public class A {
    A parent;
    A child;
    String name;
    public A(A parent) {
        this.parent = parent;
    }
}

A a = new A(null);
JavaPath javaPath = new JavaPath(A.class);
javaPath.evalPath("name",a,"PARENT");
javaPath.evalPath("child(#0).name",a,"CHILD");
javaPath.evalPath("child(#0).child(#1).name",a,"GRAND-CHILD");
assertEquals("PARENT",a.name);
assertEquals("CHILD",a.child.name);
assertEquals("GRAND-CHILD",a.child.child.name);
assertEquals("CHILD",a.child.child.parent.name);
assertEquals("PARENT",a.child.child.parent.parent.name);

— .


"a.set('$0')" //  $0

InLine :


, JavaPath. , , . .


JavaPath
"a.b.c". , evalPath , .
"a.b.c($)", .
"a.b.c($0)"$0 $ .
"a.b.c('THE VALUE')"c 'THE VALUE' evalPath . .
"a().b().c",
"a().b.c".
"a.b(int 1024).c"
"a.b(Int 1024).c"Integer
"a.b(int 1024,' ').c",
a.setX(PhoneType CELL)enum PhoneType{HOME,CELL,WORK}, "CELL"

, , valueOf ( , enum ) .


, valueOf - , StringConverter, .



- null , . .


, , , . — . Java, .


"(T a).b"

: map .


public class A {
    Map<String,String> map;
}

A a = new A();
JavaPath javaPath = new JavaPath(A.class);
//       map
javaPath.evalPath("(HashMap map).put(firstName,$)", a, "John");
//    ,     .
javaPath.evalPath("map.put(lastName,$)", a, "Silver");

.


//  HashMap      .
//        0.8 
javaPath.evalPath("(HashMap map(int 100,float '0.8')).put(firstName,$)", a, "John");

, null. map .



enum PhoneType{HOME,CELL,WORK}
public static class A {
    String firstName;
    String lastName;
    Map<PhoneType, Set<String>> phones;
    Map<String, PhoneType> reversedPhones;
}

A a = new A();
ClassRegistry  classRegistry = new ClassRegistry();
classRegistry.registerClass(PhoneType.class,PhoneType.class.getSimpleName());
JavaPath javaPath = new JavaPath(A.class,classRegistry);

javaPath.evalPath("(map phones).put(PhoneType WORK)", a, new HashSet<>());
javaPath.evalPath("phones.computeIfAbsent(PhoneType HOME,key->new HashSet).@", a);
javaPath.evalPath("phones.computeIfAbsent(PhoneType CELL,key->new HashSet).@", a);
javaPath.evalPath("(map reversedPhones).@", a);

javaPath.evalPath("firstName", a, "John");
javaPath.evalPath("lastName", a, "Smith");

javaPath.evalPath("phones.get(PhoneType CELL).add", a, "1-101-111-2233");
javaPath.evalPath("phones.get(PhoneType HOME).add", a, "1-101-111-7865");
javaPath.evalPath("phones.get(PhoneType WORK).add", a, "1-105-333-1100");
javaPath.evalPath("phones.get(PhoneType WORK).add($)", a, "1-105-333-1104");

javaPath.evalPath("reversedPhones.put($,PhoneType CELL)", a, "1-101-111-2233");
javaPath.evalPath("reversedPhones.put($,PhoneType HOME)", a, "1-101-111-7865");
javaPath.evalPath("reversedPhones.put($,PhoneType WORK)", a, "1-105-333-1100");
javaPath.evalPath("reversedPhones.put($,PhoneType WORK)", a, "1-105-333-1104");

@


@ . , . .


||


null, JavaPath . .


JavaPath
"getA∣∣setA($1).name($0)"getA null setA, getA
"getA∣∣init.name($0)"

::


, -, ::


JavaPath
"(UserInfo::newInstance userInfo).phone.ext"UserInfo UserInfo.newInstance()
"(UserInfo::newInstance userInfo(John,Smith)).phone.ext"UserInfo UserInfo.newInstance(String a, String b)
"a.b(Integer::valueOf 100).c". .
"(HashMap::new map).get"- new . .

ClassRegistry


, , .. ClassRegistry , JavaPath.


ClassRegistry . ClassRegistry, JavaPath.


PhoneType


ClassRegistry  classRegistry = new ClassRegistry();
classRegistry.registerClass(PhoneType.class,PhoneType.class.getSimpleName(),"Phone");
JavaPath javaPath = new JavaPath(A.class,classRegistry);

PhoneType , , Phone.


ClassRegistry . , :: .


. ClassRegistry . , StringConverter — .


public class A {
...
static {
    ClassRegistry.registerGlobalStringConverter(A.class,A::stringToA); 
}
public static A stringToA(String str) {
       A a = new A("{"+str+"}"); // - 
       return a;
    }
}

public class B {
    A a;
}

JavaPath javaPath = new JavaPath(B.class); //  A::stringToA

@PathElement @NoPathElement


@PathElement .


public class A {
    String name; //       "name"
    @PathElement({"name","first_name","firstName"})
    public void setName(String name) {
        this.name = name;
    }
}

, setName "name", . .


@NoPathElement JavaPath.


public class A {
    StringBuilder stringBuilder = new StringBuilder();

    @NoPathElement
    private final String protectedField = "IMMUTABLE BY JAVA PATH!";

    public void add(String str) {
        stringBuilder.append(str == null ? "N/A" : str);
    }

    @NoPathElement
    public void add(Object val) {
        stringBuilder.append(val);
    }
}

.




JavaPath . .


public class A {
    String firstName;
    String lastName;
    int age;
}

A a = new A();
JavaPath javaPath = new JavaPath(A.class);
javaPath.evalPath("firstName; lastName; age", a, "John","Smith",55);
// $       ,    
javaPath.evalPath("firstName($); lastName($); age($)", a, "John","Smith",55);
//         .
javaPath.evalPath("firstName($0); lastName($1); age($2)", a, "John","Smith",55);

'$', , . , firstName($) "John" ( , ), age($) — 55 ( , ). .


, , .


. .



JavaPath


, . , ? initPath
.


JavaPath . , . , , root. # #0


initPath .


:


//      JavaPath.  
Object instanceOfA = javaPath.initPath("(com.my.project.A #0).b", "test");
//      initPath
A instanceOfA = javaPath.initPath(A.class, "#.b", "test");
//       , #  #0
A instanceOfA = javaPath.initPath(A.class, "root.b", "test");



Mit der Methode setEnablePathCaching (boolean enableCaching) der JavaPath-Klasse können Sie das Ergebnis des Parsers im Cache speichern. Nicht zu verwechseln mit nicht deaktivierbarem Caching von Feldhierarchien und Klassenmethoden. Der Pfadcache ist standardmäßig deaktiviert, da er zu einem unkontrollierten Speicherverbrauch führen kann, wenn die Pfade dynamisch berechnet werden.


Beispiel - Der Cache enthält drei verschiedene Pfade:


evalPath("user.name('John'));"
evalPath("user.name('Peter'));"
evalPath("user.name('Mike'));"

Verwenden Sie stattdessen explizit übergebene Variablenwerte. Im unteren Beispiel wird ein Pfad gespeichert.


evalPath("user.name($0)","John");
evalPath("user.name($0)","Peter");
evalPath("user.name($0)","Mike");

Abhängigkeiten


Java8 und älter


Maven-Repository


<dependency>
    <groupId>com.aegisql</groupId>
    <artifactId>java-path</artifactId>
    <version>0.2.0</version>
</dependency>

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