在打印JSObject实现时，Nashorn运行时异常
Nashorn runtime exception while printing JSObject implementations
我有一个bean实现了JSObject (&映射)接口如下所示。为了便于阅读，我删除了一些重写的方法。
package test.nashorn;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import jdk.nashorn.api.scripting.JSObject;
public class JSBean implements JSObject, Map<String,Object>{
/**
* The current values for this object.
*/
private HashMap<String, Object> values = new HashMap<>();
@Override
public String toString() {
System.out.println("ToString");
Set<Entry<String,Object>> entries = values.entrySet();
StringBuilder sb = new StringBuilder();
for(Entry<String,Object> entry:entries){
sb.append(entry.getKey()+ " "+(String)entry.getValue());
}
System.out.println("Completed ToString");
return sb.toString();
}
@Override
public boolean hasMember(String name) {
return has(name);
}
// get the value of that named property
@Override
public Object getMember(String name) {
return get(name);
}
// get the value of that named property
@Override
public void setMember(String name,Object value) {
put(name,value);
}
public Object get(String name) {
System.out.println("JAVA Get is called."+name);
System.out.println("Called for this"+name+" and returned"
+":"+values.get(name));
return values.get(name);
}
@Override
public Object put(String name, Object value) {
System.out.println("JAVA Put is called. Input name: " + name + "'n Input values: " + value);
return values.put(name, value);
}
public boolean has(String name) {
System.out.println("JAVA Has is called. Input name: " + name);
return values.containsKey(name);
}
public JSBean() {
// TODO Auto-generated constructor stub
}
@Override
public Object call(Object arg0, Object... arg1) {
// TODO Auto-generated method stub
return null;
}
@Override
public Object eval(String arg0) {
// TODO Auto-generated method stub
return null;
}
@Override
public String getClassName() {
// TODO Auto-generated method stub
return null;
}
@Override
public Object getSlot(int arg0) {
// TODO Auto-generated method stub
return null;
}
@Override
public boolean hasSlot(int arg0) {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean isArray() {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean isFunction() {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean isInstance(Object arg0) {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean isInstanceOf(Object arg0) {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean isStrictFunction() {
// TODO Auto-generated method stub
return false;
}
}
当我运行如下所示的测试时
@Test
public void testDefaultValMethod(){
JSBean bean = new JSBean();
bean.setMember("hello", " Sport ");
//Add stuff to engine.
engine.put("jsBean", bean);
String source = "(function(){'n"
+ "print(jsBean);"
+ "} )();";
Object obj=null;
try {
obj = engine.eval(source);
} catch (ScriptException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("Returned : " + String.valueOf(obj));
}
我在控制台中看到以下错误。理想情况下，Nashorn应该直接调用bean的toString()方法来获得String实现。不知道这里出了什么问题。我确实尝试在getMember()方法调用中显式地添加对'toString()'的调用，但这并没有解决问题。
JAVA Put is called. Input name: hello
Input values: Sport
JAVA Get is called.toString
Called for thistoString and returned:null
JAVA Get is called.valueOf
Called for thisvalueOf and returned:null
javax.script.ScriptException: TypeError: cannot.get.default.string in <eval> at line number 2
at jdk.nashorn.api.scripting.NashornScriptEngine.throwAsScriptException(NashornScriptEngine.java:467)
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:451)
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:403)
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:399)
at jdk.nashorn.api.scripting.NashornScriptEngine.eval(NashornScriptEngine.java:155)
at javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:264)
at test.nashorn.NashornTest.testDefaultValMethod(NashornTest.java:386)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: <eval>:2 TypeError: cannot.get.default.string
at jdk.nashorn.internal.runtime.JSType.toPrimitive(JSType.java:514)
at jdk.nashorn.internal.runtime.JSType.toPrimitive(JSType.java:480)
at jdk.nashorn.internal.runtime.JSType.toStringImpl(JSType.java:1391)
at jdk.nashorn.internal.runtime.JSType.toString(JSType.java:589)
at jdk.nashorn.internal.objects.Global.printImpl(Global.java:2782)
at jdk.nashorn.internal.objects.Global.println(Global.java:1497)
at jdk.nashorn.internal.scripts.Script$Recompilation$1$11$'^eval'_.L:1(<eval>:2)
at jdk.nashorn.internal.scripts.Script$'^eval'_.:program(<eval>:1)
at jdk.nashorn.internal.runtime.ScriptFunctionData.invoke(ScriptFunctionData.java:640)
at jdk.nashorn.internal.runtime.ScriptFunction.invoke(ScriptFunction.java:228)
at jdk.nashorn.internal.runtime.ScriptRuntime.apply(ScriptRuntime.java:393)
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:446)
... 29 more
Caused by: java.lang.UnsupportedOperationException: cannot.get.default.string
at jdk.nashorn.api.scripting.DefaultValueImpl.getDefaultValue(DefaultValueImpl.java:53)
at jdk.nashorn.api.scripting.AbstractJSObject.getDefaultValue(AbstractJSObject.java:289)
at jdk.nashorn.internal.runtime.JSType.toPrimitive(JSType.java:512)
... 40 more
Returned : null
打印或"toString"转换从脚本调用"toString"方法对脚本对象。JSObject上的任何属性访问(包括函数值属性)都被路由到getMember方法。因此，要使"valueOf"或"toString"，你必须在JSObject子类型中实现适当的getMember。
的例子:
import jdk.nashorn.api.scripting.*;
import javax.script.*;
public class Main {
static class MyJSObject extends AbstractJSObject {
@Override
public Object getMember(String name) {
if (name.equals("toString")) {
// return a "function" object for "toString" property
return new AbstractJSObject() {
@Override
public boolean isFunction() {
return true;
}
@Override
public Object call(Object self, Object...args) {
return self.toString();
}
};
}
return null; // other properties here
}
@Override
public String toString() {
return "my js object";
}
}
public static void main(String[] a) throws Exception {
ScriptEngineManager m = new ScriptEngineManager();
ScriptEngine e = m.getEngineByName("nashorn");
e.put("myObj", new MyJSObject());
e.eval("print(myObj)");
}
}
Object getDefaultValue(final Class<?> hint) throws UnsupportedOperationException
方法在AbstractJSObject子类中。
import jdk.nashorn.api.scripting.*;
import javax.script.*;
public class Main2 {
static class MyJSObject extends AbstractJSObject {
@Override
public Object getDefaultValue(Class<?> hint) {
if (hint == String.class) {
return toString();
}
throw new UnsupportedOperationException("no conversion for " + hint);
}
@Override
public String toString() {
return "my js object";
}
}
public static void main(String[] a) throws Exception {
ScriptEngineManager m = new ScriptEngineManager();
ScriptEngine e = m.getEngineByName("nashorn");
e.put("myObj", new MyJSObject());
e.eval("print(myObj)");
}
}
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