上传文件

Author: lupingchn

java-knowledge-base/pom.xml

@@ -21,6 +21,11 @@
             <artifactId>cglib</artifactId>
             <version>3.2.4</version>
         </dependency>
+        <dependency>
+            <groupId>javassist</groupId>
+            <artifactId>javassist</artifactId>
+            <version>3.8.0.GA</version>
+        </dependency>
     </dependencies>
 
 

java-knowledge-base/src/main/java/base/bytecode/ASMCodeGenerator.java

@@ -0,0 +1,55 @@
+package base.bytecode;
+
+import org.objectweb.asm.ClassWriter;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+/**
+ * @author zhangluping on 2018/8/21.
+ */
+public class ASMCodeGenerator {
+    public static void main(String[] args) throws IOException {
+
+        System.out.println();
+        ClassWriter classWriter = new ClassWriter(0);
+        // 通过visit方法确定类的头部信息
+        classWriter.visit(Opcodes.V1_7,// java版本
+                Opcodes.ACC_PUBLIC,// 类修饰符
+                "ASMProgrammer", // 类的全限定名
+                null, "java/lang/Object", null);
+
+        //创建构造函数
+        MethodVisitor mv = classWriter.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null, null);
+        mv.visitCode();
+        mv.visitVarInsn(Opcodes.ALOAD, 0);
+        mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "java/lang/Object", "<init>", "()V");
+        mv.visitInsn(Opcodes.RETURN);
+        mv.visitMaxs(1, 1);
+        mv.visitEnd();
+
+        // 定义code方法
+        MethodVisitor methodVisitor = classWriter.visitMethod(Opcodes.ACC_PUBLIC, "code", "()V",
+                null, null);
+        methodVisitor.visitCode();
+        methodVisitor.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out",
+                "Ljava/io/PrintStream;");
+        methodVisitor.visitLdcInsn("I'm a Programmer,Just Coding.....");
+        methodVisitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println",
+                "(Ljava/lang/String;)V");
+        methodVisitor.visitInsn(Opcodes.RETURN);
+        methodVisitor.visitMaxs(2, 2);
+        methodVisitor.visitEnd();
+        classWriter.visitEnd();
+        // 使classWriter类已经完成
+        // 将classWriter转换成字节数组写到文件里面去
+        byte[] data = classWriter.toByteArray();
+        File file = new File("d://ASMProgrammer.class");
+        FileOutputStream fout = new FileOutputStream(file);
+        fout.write(data);
+        fout.close();
+    }
+}

java-knowledge-base/src/main/java/base/bytecode/ASMProgrammer.class

@@ -0,0 +1,26 @@
+package base.bytecode;
+
+import javassist.ClassPool;
+import javassist.CtClass;
+import javassist.CtMethod;
+import javassist.CtNewMethod;
+
+/**
+ * @author zhangluping on 2018/8/21.
+ */
+public class JavassistCodeGenerator {
+
+    public static void main(String[] args) throws Exception {
+        ClassPool pool = ClassPool.getDefault();
+        //创建Programmer类
+        CtClass cc = pool.makeClass("com.samples.JavassistProgrammer");
+        //定义code方法
+        CtMethod method = CtNewMethod.make("public void code(){}", cc);
+        //插入方法代码
+        method.insertBefore("System.out.println(\"I'm a Programmer,Just Coding.....\");");
+        cc.addMethod(method);
+        //保存生成的字节码
+        cc.writeFile("d://");
+    }
+
+}