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本文介紹了我找不出為什么ScriptEngine引擎在代碼中為空的處理方法，對(duì)大家解決問題具有一定的參考價(jià)值，需要的朋友們下面隨著小編來一起學(xué)習(xí)吧！

問題描述

這是我為MapleStory服務(wù)器運(yùn)行的一些代碼。每當(dāng)與NPC對(duì)話等事件的腳本應(yīng)該發(fā)生時(shí)，都會(huì)運(yùn)行此腳本來為所調(diào)用的任何腳本(NPC、門戶、事件等)創(chuàng)建腳本路徑。

我也在使用jdk1.7.0_80

lang-java
package scripting;

import java.io.File; 
import java.io.FileReader; 
import java.io.IOException;
import javax.script.Invocable; 
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import client.MapleClient; 
import tools.FileoutputUtil;

public abstract class AbstractScriptManager {

    private static final ScriptEngineManager sem = new ScriptEngineManager(null);

    protected Invocable getInvocable(String path, MapleClient c) {
        return getInvocable(path, c, false);
    }

    protected Invocable getInvocable(String path, MapleClient c, boolean npc) {
        FileReader fr = null;
        try {
            path = "scripts/" + path;
            ScriptEngine engine = null;

            if (c != null) {
                engine = c.getScriptEngine(path);
            }
            if (engine == null) {
                File scriptFile = new File(path);
                if (!scriptFile.exists()) {
                    return null;
                }
                engine = sem.getEngineByName("JavaScript");
                if (c != null) {
                    c.setScriptEngine(path, engine);
                }
                fr = new FileReader(scriptFile);
                engine.eval(fr);
            } else if (c != null && npc) {
                c.getPlayer().dropMessage(-1, "You already are talking to this NPC. Use @ea if this is 
                not intended.");
            }
            return (Invocable) engine;
        } catch (Exception e) {
            System.err.println("Error executing script. Path: " + path + "
Exception " + e);
            FileoutputUtil.log(FileoutputUtil.ScriptEx_Log, "Error executing script. Path: " + path + 
            "
Exception " + e);
            return null;
        } finally {
            try {
                if (fr != null) {
                    fr.close();
                }
            } catch (IOException ignore) {

            }
        }
    } 
}

這是我收到的BAT錯(cuò)誤：

執(zhí)行腳本時(shí)出錯(cuò)。路徑：腳本/事件/某些Event.js異常
Java.lang.NullPointerException：無法調(diào)用
&quot；javax.script.ScriptEngine.eval(java.io.Reader)&quot；，因?yàn)橐鏋榭?/p>

每當(dāng)我嘗試與使用此方法的對(duì)象交互時(shí)(例如，在運(yùn)行某些腳本時(shí)單擊NPC或啟動(dòng)服務(wù)器)，都會(huì)引發(fā)這些錯(cuò)誤。

JAVA

出現(xiàn)NullPointerException是因?yàn)槟褂玫耐扑]答案運(yùn)行時(shí)沒有安裝腳本引擎，導(dǎo)致sem.getEngineByName("JavaScript")返回null。

通過運(yùn)行以下代碼進(jìn)行了驗(yàn)證(請(qǐng)參閱comment)：

ScriptEngineManager sem = new ScriptEngineManager();
List<ScriptEngineFactory> factories = sem.getEngineFactories();
for (ScriptEngineFactory factory : factories)
    System.out.println(factory.getEngineName() + " " + factory.getEngineVersion() + " " + factory.getNames());
if (factories.isEmpty())
    System.out.println("No Script Engines found");

當(dāng)我在Windows 10上的各種Java實(shí)現(xiàn)上運(yùn)行它時(shí)，我得到以下結(jié)果：

OpenJDK jdk1.7.0_75:
  No Script Engines found

Oracle jdk1.7.0_80:
  Mozilla Rhino 1.7 release 3 PRERELEASE [js, rhino, JavaScript, javascript, ECMAScript, ecmascript]

Oracle jdk1.8.0_181:
  Oracle Nashorn 1.8.0_181 [nashorn, Nashorn, js, JS, JavaScript, javascript, ECMAScript, ecmascript]

Oracle jdk-9.0.4:
  Oracle Nashorn 9.0.4 [nashorn, Nashorn, js, JS, JavaScript, javascript, ECMAScript, ecmascript]

OpenJDK jdk-11.0.2:
  Oracle Nashorn 11.0.2 [nashorn, Nashorn, js, JS, JavaScript, javascript, ECMAScript, ecmascript]

AdoptOpenJDK jdk-14.0.2+12:
  Oracle Nashorn 14.0.2 [nashorn, Nashorn, js, JS, JavaScript, javascript, ECMAScript, ecmascript]

AdoptOpenJDK jdk-15.0.1+9:
  No Script Engines found

如您所見，Java 7的OpenJDK版本沒有Java引擎，因?yàn)镸ozilla Rhino庫(kù)不是開源的。您需要安裝Oracle版本的Java 7才能獲得Java引擎。

您還可以看到Java 15中刪除了JavaScript，如JDK 15 Release Notes：

中所述