你们中是否有人知道一种工具,可以搜索.class文件并显示它们的编译版本?
我知道你可以在十六进制编辑器中逐个查看它们,但我有很多要检查的class文件(我的巨型应用程序中有某些东西以某种原因编译为Java6)。
你们中是否有人知道一种工具,可以搜索.class文件并显示它们的编译版本?
我知道你可以在十六进制编辑器中逐个查看它们,但我有很多要检查的class文件(我的巨型应用程序中有某些东西以某种原因编译为Java6)。
使用随JDK一起提供的javap工具。使用-verbose
选项可打印类文件的版本号。
> javap -verbose MyClass
Compiled from "MyClass.java"
public class MyClass
SourceFile: "MyClass.java"
minor version: 0
major version: 46
...
仅显示版本:
WINDOWS> javap -verbose MyClass | find "version"
LINUX > javap -verbose MyClass | grep version
很容易读取类文件签名并获取这些值而无需第三方API。您只需要读取前8个字节即可。
ClassFile {
u4 magic;
u2 minor_version;
u2 major_version;
CA FE BA BE 00 00 00 33
...其中0xCAFEBABE是魔数,0x0000是小版本号,0x0033是大版本号。
import java.io.*;
public class Demo {
public static void main(String[] args) throws IOException {
ClassLoader loader = Demo.class.getClassLoader();
try (InputStream in = loader.getResourceAsStream("Demo.class");
DataInputStream data = new DataInputStream(in)) {
if (0xCAFEBABE != data.readInt()) {
throw new IOException("invalid header");
}
int minor = data.readUnsignedShort();
int major = data.readUnsignedShort();
System.out.println(major + "." + minor);
}
}
}
浏览目录(文件)和归档文件(JarFile)以查找类文件是微不足道的。
Oracle公司的Joe Darcy博客列出了Java 7之前的类版本与JDK版本的映射关系:
Target Major.minor Hex
1.1 45.3 0x2D
1.2 46.0 0x2E
1.3 47.0 0x2F
1.4 48.0 0x30
5 (1.5) 49.0 0x31
6 (1.6) 50.0 0x32
7 (1.7) 51.0 0x33
8 (1.8) 52.0 0x34
9 53.0 0x35
在类Unix操作系统上,运行命令 file /path/to/Thing.class
可以查看文件类型和版本信息。以下是输出结果示例:
已编译的Java类数据,版本号为49.0
find /target-folder -name \*.class | xargs file | grep "version 50\.0"
我的文件版本显示为“编译的Java类数据,版本50.0”,适用于Java6类。
`file *.class`
产生的结果是:`ClassName.class: 编译后的Java类数据,版本为50.0(Java 1.6)`
- Gary又一个Java版本检查
od -t d -j 7 -N 1 ApplicationContextProvider.class | head -1 | awk '{print "Java", $2 - 44}'
类Unix系统: hexdump -s 7 -n 1 -e '"%d"' Main.class
Windows系统: busybox.exe hexdump -s 7 -n 1 -e '"%d"' Main.class
55
-s 7
偏移量为7-n 1
限制为1-e '"%d"'
转换为十进制输出JDK 1.1 = 45 (0x2D hex)
JDK 1.2 = 46 (0x2E hex)
JDK 1.3 = 47 (0x2F hex)
JDK 1.4 = 48 (0x30 hex)
Java SE 5.0 = 49 (0x31 hex)
Java SE 6.0 = 50 (0x32 hex)
Java SE 7 = 51 (0x33 hex)
Java SE 8 = 52 (0x34 hex)
Java SE 9 = 53 (0x35 hex)
Java SE 10 = 54 (0x36 hex)
Java SE 11 = 55 (0x37 hex)
Java SE 12 = 56 (0x38 hex)
Java SE 13 = 57 (0x39 hex)
Java SE 14 = 58 (0x3A hex)
Java SE 15 = 59 (0x3B hex)
Java SE 16 = 60 (0x3C hex)
Java SE 17 = 61 (0x3D hex)
System.out.println("JAVA DEV ver.: " + com.sun.deploy.config.BuiltInProperties.CURRENT_VERSION);
System.out.println("JAVA RUN v. X.Y: " + System.getProperty("java.specification.version") );
System.out.println("JAVA RUN v. W.X.Y.Z: " + com.sun.deploy.config.Config.getJavaVersion() ); //_javaVersionProperty
System.out.println("JAVA RUN full ver.: " + System.getProperty("java.runtime.version") + " (may return unknown)" );
System.out.println("JAVA RUN type: " + com.sun.deploy.config.Config.getJavaRuntimeNameProperty() );
输出:
JAVA DEV ver.: 1.8.0_77
JAVA RUN v. X.Y: 1.8
JAVA RUN v. W.X.Y.Z: 1.8.0_91
JAVA RUN full ver.: 1.8.0_91-b14 (may return unknown)
JAVA RUN type: Java(TM) SE Runtime Environment
在类字节码中,实际上存储了常量 - 参见Main.call中标记为红色的部分- 常量存储在.class字节码中。
常量用于检查JAVA版本是否过时(请参见Java如何检查是否过时)......
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import org.apache.commons.codec.DecoderException;
import org.apache.commons.codec.binary.Hex;
import org.apache.commons.io.IOUtils;
public class Main {
public static void main(String[] args) throws DecoderException, IOException {
Class clazz = Main.class;
Map<String,String> versionMapping = new HashMap();
versionMapping.put("002D","1.1");
versionMapping.put("002E","1.2");
versionMapping.put("002F","1.3");
versionMapping.put("0030","1.4");
versionMapping.put("0031","5.0");
versionMapping.put("0032","6.0");
versionMapping.put("0033","7");
versionMapping.put("0034","8");
versionMapping.put("0035","9");
versionMapping.put("0036","10");
versionMapping.put("0037","11");
versionMapping.put("0038","12");
versionMapping.put("0039","13");
versionMapping.put("003A","14");
InputStream stream = clazz.getClassLoader()
.getResourceAsStream(clazz.getName().replace(".", "/") + ".class");
byte[] classBytes = IOUtils.toByteArray(stream);
String versionInHexString =
Hex.encodeHexString(new byte[]{classBytes[6],classBytes[7]});
System.out.println("bytecode version: "+versionMapping.get(versionInHexString));
}
}
另一个可以检查类是否使用预览功能编译的参考:
public final class JavaClassVersion {
private final int major;
private final int minor;
private JavaClassVersion(int major, int minor) {
this.major = major;
this.minor = minor;
}
public int major() {
return major;
}
public int minor() {
return minor;
}
public static JavaClassVersion of(Path artifactPath) {
try (InputStream in = Files.newInputStream(artifactPath);
DataInputStream data = new DataInputStream(in)) {
if (0xCAFEBABE != data.readInt()) {
throw new IOException("invalid header");
}
int minor = data.readUnsignedShort();
int major = data.readUnsignedShort();
return new JavaClassVersion(major, minor);
} catch (IOException ex) {
throw new UncheckedIOException(ex);
}
}
String getJavaVersion() {
switch (major) {
case 50:
return "1.6";
case 51:
return "1.7";
case 52:
return "1.8";
case 53:
return "9";
case 54:
return "10";
case 55:
return "11";
case 56:
return "12";
case 57:
return "13";
case 58:
return "14";
case 59:
return "15";
case 60:
return "16";
case 61:
return "17";
case 62:
return "18";
case 63:
return "19";
case 64:
return "20";
case 65:
return "21";
default:
return "";
}
}
boolean isPreview() {
return minor == 65535;
}
}