Java中使用JavaScript脚本的方法步骤

在Java中使用JavaScript脚本的方法步骤大致如下：

1. 导入JavaScript引擎
2. Java 8及以后版本使用Nashorn引擎（已废弃）：
   ```java
   import javax.script.ScriptEngineManager;
   import javax.script.ScriptEngine;

ScriptEngineManager factory = new ScriptEngineManager();
ScriptEngine engine = factory.getEngineByName("nashorn");
- Java 11及以后版本使用GraalVM引擎：java
import org.graalvm.polyglot.Context;

Context graalVMContext = Context.newBuilder("js").build();
```

1. 载入JavaScript脚本文件或直接执行脚本字符串

2. 从文件载入脚本：

```java
import java.io.FileReader;

FileReader reader = new FileReader("path/to/script.js");
engine.eval(reader);
```

• 直接执行脚本字符串：

java
String script = "function square(number) { return number * number; }";
engine.eval(script);

1. 调用JavaScript函数和获取脚本返回值

2. 调用JavaScript函数：

```java
// 假设在脚本中定义了一个名为add的函数
String script = "function add(a, b) { return a + b; }";
engine.eval(script);

// 调用这个函数
Invocable invocable = (Invocable) engine;
Object result = invocable.invokeFunction("add", 1, 2);
// 此时result的值为3
```

• 获取脚本返回值：

java
String script = "var x = 2 * 3; x;";
Object result = engine.eval(script);
// 此时result的值为6

示例1：从文件载入脚本并调用JavaScript函数

import javax.script.*;
import java.io.*;

public class Example1 {
    public static void main(String[] args) throws Exception {
      ScriptEngineManager factory = new ScriptEngineManager();
      ScriptEngine engine = factory.getEngineByName("nashorn");

      FileReader reader = new FileReader("path/to/script.js");
      engine.eval(reader);

      Invocable invocable = (Invocable) engine;
      Object result = invocable.invokeFunction("myFunction", "John");
      System.out.println(result);
    }
}

示例2：直接执行脚本字符串并获取脚本返回值

import javax.script.*;

public class Example2 {
    public static void main(String[] args) throws Exception {
      ScriptEngineManager factory = new ScriptEngineManager();
      ScriptEngine engine = factory.getEngineByName("nashorn");

      String script = "var x = 2 * 3; x;";
      Object result = engine.eval(script);
      System.out.println(result);
    }
}