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

JavaPath . . , , , . . , , , .. — .
$ #

, evalPath $[:digit:]* . $ , . .
.
. : #[:digit:]* # #0
.
, -.
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('$0')"
InLine :
, JavaPath. , , . .
, , valueOf ( , enum ) .
, valueOf - , StringConverter, .
- null , . .
, , , . — . Java, .
"(T a).b"
: map .
public class A {
Map<String,String> map;
}
A a = new A();
JavaPath javaPath = new JavaPath(A.class);
// map
javaPath.evalPath("(HashMap map).put(firstName,$)", a, "John");
// , .
javaPath.evalPath("map.put(lastName,$)", a, "Silver");
.
javaPath.evalPath("(HashMap map(int 100,float '0.8')).put(firstName,$)", 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($,PhoneType WORK)", a, "1-105-333-1104");
@
@ . , . .
||
null, JavaPath . .
::
, -, ::
ClassRegistry
, , .. ClassRegistry , JavaPath.
ClassRegistry . ClassRegistry, JavaPath.
PhoneType
ClassRegistry classRegistry = new ClassRegistry();
classRegistry.registerClass(PhoneType.class,PhoneType.class.getSimpleName(),"Phone");
JavaPath javaPath = new JavaPath(A.class,classRegistry);
PhoneType , , Phone.
ClassRegistry . , :: .
. ClassRegistry . , StringConverter — .
public class A {
...
static {
ClassRegistry.registerGlobalStringConverter(A.class,A::stringToA);
}
public static A stringToA(String str) {
A a = new A("{"+str+"}");
return a;
}
}
public class B {
A a;
}
JavaPath javaPath = new JavaPath(B.class); // A::stringToA
@PathElement @NoPathElement
@PathElement .
public class A {
String name;
@PathElement({"name","first_name","firstName"})
public void setName(String name) {
this.name = name;
}
}
, setName "name", . .
@NoPathElement JavaPath.
public class A {
StringBuilder stringBuilder = new StringBuilder();
@NoPathElement
private final String protectedField = "IMMUTABLE BY JAVA PATH!";
public void add(String str) {
stringBuilder.append(str == null ? "N/A" : str);
}
@NoPathElement
public void add(Object val) {
stringBuilder.append(val);
}
}
.
JavaPath . .
public class A {
String firstName;
String lastName;
int age;
}
A a = new A();
JavaPath javaPath = new JavaPath(A.class);
javaPath.evalPath("firstName; lastName; age", a, "John","Smith",55);
javaPath.evalPath("firstName($); 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 .
:
Object instanceOfA = javaPath.initPath("(com.my.project.A #0).b", "test");
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>