Java动态编译

JDK1.6加入了编译API，开发者可以在代码中调用API，从而动态编译Java源代码，下面举个例子来讲解具体用法。

直接上源码

package cn.o.test;

import javax.tools.*;
import java.io.*;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.tools.JavaCompiler.CompilationTask;

public class DynamicCompiler {

    /**
     * 匹配包名的正则
     */
    private static final String REG_EX = "(?<=package\\s).*(?=;)";
    /**
     * 缓存已编译的脚本的名称和Hash值，Map<类名, Hash值>
     */
    private static Map<String, String> classCache = new HashMap<>();

    /**
     * 编译源码，返回Class
     * @srcFilePath: 源文件绝对路径
     */
    public static Class compile(String srcFilePath) throws Exception {

        // 实例化编译器
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        // 实例化源文件管理器
        StandardJavaFileManager fileManager
                = compiler.getStandardFileManager(null, null, null);
        // 实例化日志管理器
        DiagnosticCollector<JavaFileObject> diagnostics
                = new DiagnosticCollector<JavaFileObject>();

        // 通过文件名获取类名
        File srcFile = new File(srcFilePath);
        String className = srcFile.getName();
        // 解析包名，获得类全名
        String packageName = getPackageName(srcFilePath);
        String fullClassName = packageName + "." + className;

        // 获取源码的hash
        String hash = String.valueOf(readFile(srcFilePath).hashCode());
        // 通过比较类名对应的Hash，判断类是否已编译过，且是否更改
        String originalHash = classCache.get(fullClassName);
        // 如果源码未做改动，则直接返回已编译过的类
        if (originalHash != null && hash.equals(originalHash)) {
            return Class.forName(fullClassName);
        }

        // 获取要编译的编译单元
        List<File> srcFileList = new ArrayList<File>();
        srcFileList.add(srcFile);
        Iterable<? extends JavaFileObject> compilationUnits
                = fileManager.getJavaFileObjectsFromFiles(srcFileList);
        /*
         * 编译参数，
         * -encoding：编码方式为utf-8
         * -classpath：依赖包和依赖的classpath绝对路径，用半角冒号:隔开
         * -d：编译的目标绝对路径
         */
        String dependencies = "/lib/ABC.jar:/lib/DEF.jar:/lib/GHI.jar";
        String targetPath = "/compile/source/to/this/path";
        Iterable<String> options = Arrays.asList(
                "-encoding", "utf-8",
                "-classpath", dependencies,
                "-d", targetPath);
        // 获取编译任务
        CompilationTask compilationTask = compiler.getTask(
                null, fileManager, diagnostics, options, null, compilationUnits);
        // 运行编译任务
        Boolean result = compilationTask.call();
        if (!result) {
            // 此处可以DEBUG查看或打印diagnostics对象的内容，从而查看编译失败原因
            throw new Exception(fullClassName + "编译失败。");
        }
        // 销毁文件管理器
        fileManager.close();
        // 储存编译的类的hash
        classCache.put(fullClassName, hash);
        return Class.forName(fullClassName);
    }

    /**
     * 从源文件中获得包名
     * @param srcPath
     */
    private static String getPackageName(String srcPath) throws Exception {
        String result = null;
        BufferedReader br;
        Pattern packagePattern = Pattern.compile(REG_EX);
        try {
            br = new BufferedReader(new FileReader(srcPath));
            String data = br.readLine();
            while (data != null) {
                if (data.indexOf("package") != -1) {
                    Matcher m = packagePattern.matcher(data);
                    if (m.find()) {
                        result = m.group();
                    }
                    break;
                }
                data = br.readLine();
            }
            br.close();
        } catch (IOException e) {
            throw new Exception("获取包名失败");
        }
        return result;
    }

    /**
     * 读取源码内容
     * @srcFilePath: 源文件绝对路径
     */
    private static String readFile(String srcFilePath) {
        BufferedReader br = null;
        String line = null;
        StringBuffer buf = new StringBuffer();
        try {
            br = new BufferedReader(new InputStreamReader(new FileInputStream(srcFilePath), "UTF-8"));
            while ((line = br.readLine()) != null) {
                buf.append(line).append("\n");
            }
        } catch (Exception e) {

        } finally {
            // 关闭流
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    br = null;
                }
            }
        }
        return buf.toString();
    }
}

调用方式

public static void main(String[] args) {
    Class klass = DynamicCompiler.compile("/absolute/path/of/java/source/file.java");
    Object object = klass.newInstance();
    // do something
}