我使用类似于Rhino交互式shell的相当简单的方法(请参阅我在问题结尾处的注释)实现了可与Java SE 6 Rhino(Javascript)和Jython 1.5.2(Python)一起工作的一些东西:
- 保留尚未评估的待处理输入行列表。
- 尝试编译(但不评估)悬而未决的输入行。
- 如果编译正常,我们可能能够执行悬而未决的输入行。
- 如果编译引发异常,并且有错误位置(行+列号)的指示,并且这与未决输入的结尾相匹配,那么这就是我们期待更多输入的线索,所以吞下异常并等待下一行。
- 否则,我们要么不知道错误在哪里,要么发生在悬而未决的输入结束之前,因此重新抛出异常。
- 如果我们不期待更多的输入行,并且我们只有一行待定输入,然后评估它并重新启动。
- 如果我们不期待更多的输入行,并且最后一行是空白行(per @ karakuricoder的答案),并且我们有多行未决输入,则评估它并重新启动。 Python的交互式shell似乎这样做。
- 否则,请继续阅读输入行。
我没有要发生什么,或者是:
- 用户生气不必输入单行输入
- 用户输入一个长的多行语句之后,多余的空行只有在第二行出现语法错误后才能查明。
这里是一个辅助类,我写的是我的执行办法:
import java.lang.reflect.Method;
import javax.script.Bindings;
import javax.script.Compilable;
import javax.script.CompiledScript;
import javax.script.ScriptEngine;
import javax.script.ScriptException;
public class ScriptEngineInterpreter
{
private static final boolean DEBUG = false;
final private ScriptEngine engine;
final private Bindings bindings;
final private StringBuilder sb;
private int lineNumber;
private int pendingLineCount;
private boolean expectingMoreInput;
/**
* @param engine ScriptingEngine to use in this interpreter
* @param bindings Bindings to use in this interpreter
*/
public ScriptEngineInterpreter(ScriptEngine engine, Bindings bindings)
{
this.engine = engine;
this.bindings = bindings;
this.sb = new StringBuilder();
this.lineNumber = 0;
reset();
}
/** @return ScriptEngine used by this interpreter */
public ScriptEngine getEngine() { return this.engine; }
protected void reset() {
this.sb.setLength(0);
this.pendingLineCount = 0;
setExpectingMoreInput(false);
}
/** @return whether the interpreter is ready for a brand new statement. */
public boolean isReady() { return this.sb.length() == 0; }
/**
* @return whether the interpreter expects more input
*
* A true value means there is definitely more input needed.
* A false value means no more input is needed, but it may not yet
* be appropriate to evaluate all the pending lines.
* (there's some ambiguity depending on the language)
*/
public boolean isExpectingMoreInput() { return this.expectingMoreInput; }
protected void setExpectingMoreInput(boolean b) { this.expectingMoreInput = b; }
/**
* @return number of lines pending execution
*/
protected int getPendingLineCount() { return this.pendingLineCount; }
/**
* @param lineIsEmpty whether the last line is empty
* @return whether we should evaluate the pending input
* The default behavior is to evaluate if we only have one line of input,
* or if the user enters a blank line.
* This behavior should be overridden where appropriate.
*/
protected boolean shouldEvaluatePendingInput(boolean lineIsEmpty)
{
if (isExpectingMoreInput())
return false;
else
return (getPendingLineCount() == 1) || lineIsEmpty;
}
/**
* @param line line to interpret
* @return value of the line (or null if there is still pending input)
* @throws ScriptException in case of an exception
*/
public Object interpret(String line) throws ScriptException
{
++this.lineNumber;
if (line.isEmpty())
{
if (!shouldEvaluatePendingInput(true))
return null;
}
++this.pendingLineCount;
this.sb.append(line);
this.sb.append("\n");
CompiledScript cs = tryCompiling(this.sb.toString(), getPendingLineCount(), line.length());
if (cs == null)
{
return null;
}
else if (shouldEvaluatePendingInput(line.isEmpty()))
{
try
{
Object result = cs.eval(this.bindings);
return result;
}
finally
{
reset();
}
}
else
{
return null;
}
}
private CompiledScript tryCompiling(String string, int lineCount, int lastLineLength)
throws ScriptException
{
CompiledScript result = null;
try
{
Compilable c = (Compilable)this.engine;
result = c.compile(string);
}
catch (ScriptException se) {
boolean rethrow = true;
if (se.getCause() != null)
{
Integer col = columnNumber(se);
Integer line = lineNumber(se);
/* swallow the exception if it occurs at the last character
* of the input (we may need to wait for more lines)
*/
if (col != null
&& line != null
&& line.intValue() == lineCount
&& col.intValue() == lastLineLength)
{
rethrow = false;
}
else if (DEBUG)
{
String msg = se.getCause().getMessage();
System.err.println("L"+line+" C"+col+"("+lineCount+","+lastLineLength+"): "+msg);
System.err.println("in '"+string+"'");
}
}
if (rethrow)
{
reset();
throw se;
}
}
setExpectingMoreInput(result == null);
return result;
}
private Integer columnNumber(ScriptException se)
{
if (se.getColumnNumber() >= 0)
return se.getColumnNumber();
return callMethod(se.getCause(), "columnNumber", Integer.class);
}
private Integer lineNumber(ScriptException se)
{
if (se.getLineNumber() >= 0)
return se.getLineNumber();
return callMethod(se.getCause(), "lineNumber", Integer.class);
}
static private Method getMethod(Object object, String methodName)
{
try {
return object.getClass().getMethod(methodName);
}
catch (NoSuchMethodException e) {
return null;
/* gulp */
}
}
static private <T> T callMethod(Object object, String methodName, Class<T> cl) {
try {
Method m = getMethod(object, methodName);
if (m != null)
{
Object result = m.invoke(object);
return cl.cast(result);
}
}
catch (Exception e) {
e.printStackTrace();
}
return null;
}
}
......以及如何帮助?如果没有ScriptingEngine本身的帮助,我该如何区分不完整的陈述和完整的陈述? – 2011-04-07 17:08:20
“在空行输入信号表示用户输入的结束” - ICK - 可以工作,但是很烦人。 – 2011-04-07 17:14:57
没有什么可以阻止来自任何流的不完整语句,无论是文件,网络连接还是键盘。您必须进行一些预先验证,否则eval impl将不得不采取必要的措施来处理/验证陈述未完成。其次,每个流都必须有一个结束标记。从非键盘流中读取返回一些标志值,例如EOF,-1,null等。您可以选择任何您希望用于输入结尾的方式,但必须通过编程方式来确定用户已完成。 – karakuricoder 2011-04-08 02:41:40