利用JavaCompiler动态编译代码

JavaCompiler
JavaCompiler, 动态编译

Java Compiler API

在Java 6中javax.tools提供了标准的包来操作Java编译器，使得我们可以在程序运行期中动态加载Java类，来实现个性化的操作。实际应用可以在一些业务变化多的服务中，将共同操作抽象出来后，再针对不同业务场景动态加载编写的有业务属性的逻辑。

以一个简单的实际例子：

新建抽象基础类：JavaDynamicScript

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public abstract class JavaDynamicScript {

    public abstract Object script(Map<String, Object> context);

}

编写动态类代码：

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import com.jinzl.compiler.dto.JavaDynamicScript;
import java.util.Map;
public class HelloWorldScript extends JavaDynamicScript {

    private String content;

    @Override
    public Object script(Map<String, Object> context) {
        System.out.println("脚本开始执行");
        System.out.println("内部变量content: " + content);
        System.out.println("执行上下文context: " + context);
        System.out.println("脚本结束执行");
        return content;
    }
}

包装JavaCompilier

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public class JavaCodeCompiler {

    public JavaCodeCompiler() throws MalformedURLException {}

    private JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

    private final String libDir = StringUtils.substringBeforeLast(ResourceUtils.extractArchiveURL(JavaDynamicScript.class.getResource("")).getPath(), "/");
    private final String classPath = System.getProperty("java.class.path");
    private static final String JAVA_CODE_FILE_PATH = "string";

    private static final StringJavaFileManager STRING_JAVA_FILE_MANAGER = CompilerConfig.standardFileManager();


    public boolean compiler(String fullClassName, String sourceCode, DiagnosticCollector<JavaFileObject> diagnosticCollector){
        long startTime = System.currentTimeMillis();
        long compilerTakeTime;

        JavaFileObject javaFileObject = new StringJavaFileObject(JAVA_CODE_FILE_PATH, fullClassName, sourceCode);
        Iterable<String> options = Arrays.asList("-classpath", classPath, "-extdirs", libDir);

        JavaCompiler.CompilationTask task = compiler.getTask(null, STRING_JAVA_FILE_MANAGER, diagnosticCollector, options, null, Arrays.asList(javaFileObject));
        compilerTakeTime = System.currentTimeMillis() - startTime;

        System.out.println("script compile success, class=" + fullClassName + ", time=" + compilerTakeTime);
        return task.call();
    }

}

使用 ToolProvider.getSystemJavaCompiler() 拿到JavaCompiler接口的实例。
这里还需要提供文件管理服务类

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public class StringJavaFileObject extends SimpleJavaFileObject {

    private String contents;

    public StringJavaFileObject(String path, String className, String contents){
        super(URI.create(path + ":///" + className.replaceAll("\\.", "/") + Kind.SOURCE.extension), Kind.SOURCE);
        this.contents = contents;
    }

    @Override
    public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
        return contents;
    }
}

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