动态编译.java文件

前两天遇到一个数据计算问题，数据计算公式有时候可能会变，考虑用动态生成.java文件，然后动态去加载.class文件的方法去解决，先做一下记录，以备用时查看：

import javax.tools.JavaCompiler;
import javax.tools.SimpleJavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.net.URI;
import java.util.Arrays;


public class ComputeService {

    public boolean compile(String formulate,String packageName,String className){
        if(null == formulate || "".equals(formulate)){
            return false;
        }

        StringBuffer sb = new StringBuffer();

        sb.append("package ");
        sb.append(packageName + ";");
        sb.append("\n");

        sb.append("public class " );
        sb.append(className);
        sb.append("{");
        sb.append("public void compute(){");

        sb.append(formulate);
        sb.append("}}");

        String classPath = Thread.currentThread().getContextClassLoader().getResource("//").getPath();

        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        JavaStringFileObject fileObject = new JavaStringFileObject(className,sb.toString());


        StandardJavaFileManager fileManager = compiler.getStandardFileManager(null,null,null);

        JavaCompiler.CompilationTask task = compiler.getTask(null, fileManager, null, Arrays.asList("-d", classPath), null, Arrays.asList(fileObject));


        return task.call();
    }



    class JavaStringFileObject extends SimpleJavaFileObject{

        private String javaSource;
        public JavaStringFileObject(String className,String javaSource){
            super(URI.create(className + ".java"), Kind.SOURCE);
            this.javaSource = javaSource;
        }

        public CharSequence getCharContent(boolean ignoreEncodingErrors){
            return javaSource;
        }

    }
}

当java文件编译完成并加载后，就可以用java反射生成java对象，进行计算了。