java - 如何在运行时将 jar 添加到 classPatch 以解决编译后的类包导入问题

Question

我制作了一个简单的Java编译器工具，它编译作为字符串传递的类，如果编译失败，结果将作为字符串重新调整(正常或编译错误)。它与一个仅导入 jre 中包含的包的类一起使用。当类导入未包含在 classPatch 中的包时，会发生编译错误 - 正如目前所料。问题是，当我检查导入外部包的类时，我想在运行时加载该包，以便编译器能够解析导入。我正在检查所有可能的解决方案，包括系统类加载器、上下文类加载器、所有可能的工具，例如 JCL classloader (除了 OSGI 容器，我不想使用它)，但似乎没有什么能像我需要的那样工作。它只是返回类对象，您可以在其中获取它的实例并调用方法。那不是我需要的。这是我的编译器代码:

import javax.tools.JavaCompiler;
import javax.tools.ToolProvider;
import java.io.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
 * Plugins compiler - checks if Java class is correct. If compilation is correct it returns "OK", otherwise it returns compiler error.
 */
public class PluginsCompiler
{

    public static final File TEMP_DIR = new File("C://YourDir//");

    public String compile(String javaSource) throws IOException
    {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        /*
         * We create our own OutputStream, which simply writes error into String
         */
        OutputStream output = new OutputStream()
        {
            private StringBuilder sb = new StringBuilder();

            @Override
            public void write(int b) throws IOException
            {
                this.sb.append((char) b);
            }

            @Override
            public String toString()
            {
                return this.sb.toString();
            }
        };

        /*
         * We need to write file temporary before compiling it
         */
        String classNameWithPath =
                        TEMP_DIR.getAbsolutePath().toString() + "\\" + this.getClassName(javaSource)
                                        + ".java";
        File file = new File(classNameWithPath);

       /*
        * if file doesn't exists, then we create it
        */
        if (!file.exists())
        {
            file.createNewFile();
        }

        try
        {
            FileWriter fw = new FileWriter(file.getAbsoluteFile());
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write(javaSource);
            bw.close();
            compiler.run(null, null, output, classNameWithPath);
        }
        finally
        {
            for (File f : TEMP_DIR.listFiles())
            {
                f.delete();
            }
        }
        return output.toString().length() == 0 ? "OK" : output.toString();
    }

    private String getClassName(String classSource)
    {
        Pattern patter = Pattern.compile("(class\\s)(\\w+)(\\s|\\\\n|\\{)");
        Matcher matcher = patter.matcher(classSource);
        String className = "";

        if (matcher.find())
        {
            className = matcher.group(2);
        }

        return className;
    }

    public static void main(String[] args) throws IOException
    {
        String testSource = "package com.test;\n"
                        + "import java.io.IOException;\n"
                        + "public class ExternaPlugin\n"
                        + "{\n"
                        + "    public void foo(String title, String message) throws IOException\n"
                        + "    {\n"
                        + "        System.out.println(title + \" \" + message);\n"
                        + "    }\n"
                        + "}\n";

        PluginsCompiler compiler = new PluginsCompiler();
        System.out.println(compiler.compile(testSource));
    }
}

例如，如果测试类如下所示:

import static org.junit.Assert.assertEquals;   
import org.junit.Test;

public class MyTests{

  @Test
  public void multiplicationOfZeroIntegersShouldReturnZero() {

    // assert statements
    assertEquals("10 x 0 must be 0", 0, 10 * 0);

  }
} 

由于未解析导入，编译将失败。所以我想加载包 junit-4.12.jar 这样编译器就会解析这个包。有什么办法可以做到吗？

Answer 1

您可以将修改后的类路径传递给编译器，如代码片段中所示。

File[] files = new File[]{new File("/path/to/source/MyTests.java")};

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

String classPath = System.getProperty("java.class.path");
String testpath = classPath + ";/path/to/lib/junit-4.10.jar";

List<String> options = new ArrayList<>();
options.addAll(Arrays.asList("-classpath", testpath));

try (StandardJavaFileManager filemanager = compiler.getStandardFileManager(
        null, null, null)) {
    Iterable fileObjects = filemanager.getJavaFileObjects(files);
    JavaCompiler.CompilationTask task = compiler.getTask(
            null, null, null, options, null, fileObjects);
    task.call();
}