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ModuleBootstrap.java
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ModuleBootstrap.java
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/*
* Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package jdk.internal.module;
import java.io.File;
import java.io.PrintStream;
import java.lang.module.Configuration;
import java.lang.module.ModuleDescriptor;
import java.lang.module.ModuleFinder;
import java.lang.module.ModuleReference;
import java.lang.module.ResolvedModule;
import java.net.URI;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;
import jdk.internal.loader.BootLoader;
import jdk.internal.loader.BuiltinClassLoader;
import jdk.internal.misc.JavaLangAccess;
import jdk.internal.misc.JavaLangModuleAccess;
import jdk.internal.misc.SharedSecrets;
import jdk.internal.perf.PerfCounter;
/**
* Initializes/boots the module system.
*
* The {@link #boot() boot} method is called early in the startup to initialize the module system.
* In summary, the boot method creates a Configuration by resolving a set of module names specified via the launcher (or equivalent) -m and --add-modules options.
* The modules are located on a module path that is constructed from the upgrade module path, system modules, and application module path.
* The Configuration is instantiated as the boot layer with each module in the configuration defined to a class loader.
*/
// 模块系统启动器
public final class ModuleBootstrap {
// the token for "all default modules"
private static final String ALL_DEFAULT = "ALL-DEFAULT";
// the token for "all system modules"
private static final String ALL_SYSTEM = "ALL-SYSTEM";
// the token for "all modules on the module path"
private static final String ALL_MODULE_PATH = "ALL-MODULE-PATH";
private static final String JAVA_BASE = "java.base"; // 基础模块
// the token for "all unnamed modules"
private static final String ALL_UNNAMED = "ALL-UNNAMED";
private static final String ADD_MODULES = "--add-modules";
private static final String ADD_EXPORTS = "--add-exports";
private static final String ADD_OPENS = "--add-opens";
private static final String ADD_READS = "--add-reads";
private static final String PATCH_MODULE = "--patch-module";
// access to java.lang/module
private static final JavaLangModuleAccess JLMA = SharedSecrets.getJavaLangModuleAccess();
/** The ModulePatcher for the initial configuration */
/*
* --patch-module信息，"--patch-module"名称在系统内部被转换为"jdk.module.patch.{序号}"
*
* --patch-module用来将目录或jar包中的class文件添加/覆盖到指定module，通常在测试环节使用。
*/
private static final ModulePatcher patcher = initModulePatcher();
// ModuleFinders for the initial configuration
private static volatile ModuleFinder unlimitedFinder; // 应用"--limit-modules"前的模块查找器
private static volatile ModuleFinder limitedFinder; // 应用"--limit-modules"后的模块查找器
private ModuleBootstrap() {
}
/**
* Initialize the module system, returning the boot layer.
*
* @see java.lang.System#initPhase2(boolean, boolean)
*/
/*
* 初始化模块系统，返回模块层
*
* 注：关于命令行参数名称与系统内部使用的参数名称之间的转换，参见openjdk\src\hotspot\share\runtime\arguments.cpp文件
*/
public static ModuleLayer boot() throws Exception {
// Step 0: Command line options
long t0 = System.nanoTime();
/*
* module-path可以分为三类
*
* compilation module path，由--module-source-path指定，表示模块源码，仅在javac中使用
* application module path，由--module-path指定，表示已编译的应用模块
* upgrade module path，由--upgrade-module-path指定，表示用来替换运行环境中可升级模块的已编译模块
*
* --module-path将不包含模块声明的jar识别为automatic module。
*/
// 基于"--upgrade-module-path"的模块查找器("--upgrade-module-path"名称在系统内部被转换为"jdk.module.upgrade.path")
ModuleFinder upgradeModulePath = finderFor("jdk.module.upgrade.path");
// 基于"--module-path"的模块查找器("--module-path"名称在系统内部被转换为"jdk.module.path")
ModuleFinder appModulePath = finderFor("jdk.module.path");
// 是否包含--patch-module信息
boolean isPatched = patcher.hasPatches();
// 获取"jdk.module.main"信息，即主模块信息，由-m指定
String mainModule = System.getProperty("jdk.module.main");
/*
* 获取"--add-module"信息。
*
* --add-module用来添加额外的模块到根模块集合中。
*/
Set<String> addModules = addModules();
/*
* 获取"--limit-modules"信息。
*
* 用来限定编译及运行时可以使用的模块，限定的范围是main module，--add-modules添加的modules，
* 以及该参数指定的modules及其transitive依赖的modules。
*
* 当包含main方法的module是unnamed modules的时候，经常用这个参数来减少需要被解析的模块数量。
*/
Set<String> limitModules = limitModules();
PrintStream traceOutput = null;
/*
* 获取key为"jdk.module.showModuleResolution"的系统属性的value，并将该条属性从系统属性集中移除。
* 注：被移除的属性可以去VM#savedProps中查找
*
* "jdk.module.showModuleResolution"属性由"--show-module-resolution"映射而来
*/
String trace = getAndRemoveProperty("jdk.module.showModuleResolution");
if(Boolean.parseBoolean(trace)) {
traceOutput = System.out; // 到达此处时，System.out已有值
}
/*
* Step 1:
*
* The observable system modules, either all system modules or the system modules pre-generated for the initial module
* (the initial module may be the unnamed module).
* If the system modules are pre-generated for the initial module then resolution can be skipped.
*/
long t1 = System.nanoTime();
// 系统模块，包含运行环境锁提供的已编译模块
SystemModules systemModules = null;
ModuleFinder systemModuleFinder;
// 是否存在模块查找器("--module-path"、"--upgrade-module-path")
boolean haveModulePath = (appModulePath != null || upgradeModulePath != null);
// 是否需要后续处理，如果没有通过命令行显式引入其他模块，则不需要后续处理
boolean needResolution = true;
if(!haveModulePath // 不包含"--module-path"或"--upgrade-module-path"信息
&& addModules.isEmpty() // 不包含"--add-module"信息
&& limitModules.isEmpty()) { // 不包含"--limit-modules"信息
// 获取初始模块关联的系统模块信息
systemModules = SystemModuleFinders.systemModules(mainModule);
// noinspection ConstantConditions
if(systemModules != null // 包含系统模块
&& !isPatched // 不包含--patch-module信息
&& traceOutput == null) { // 不需要追踪输出
// 后续不再需要解析
needResolution = false;
}
}
// 获取所有系统模块信息
if(systemModules == null) {
// all system modules are observable
systemModules = SystemModuleFinders.allSystemModules();
}
// 获取外部模块信息
if(systemModules == null) {
// exploded build or testing
systemModules = new ExplodedSystemModules();
systemModuleFinder = SystemModuleFinders.ofSystem();
// 构造系统模块集的模块查找器
} else {
// images build
systemModuleFinder = SystemModuleFinders.of(systemModules);
}
Counters.add("jdk.module.boot.1.systemModulesTime", t1);
/*
* Step 2:
*
* Define and load java.base.
* This patches all classes loaded to date so that they are members of java.base.
* Once java.base is loaded then resources in java.base are available for error messages needed from here on.
*/
long t2 = System.nanoTime();
// 获取"java.base"模块的引用
ModuleReference base = systemModuleFinder.find(JAVA_BASE).orElse(null);
if(base == null) {
throw new InternalError(JAVA_BASE + " not found");
}
// 获取"java.base"模块位置
URI baseUri = base.location().orElse(null);
if(baseUri == null) {
throw new InternalError(JAVA_BASE + " does not have a location");
}
// 将加载的"java.base"模块信息注册到BootClassLoader中
BootLoader.loadModule(base);
// 构造"java.base"模块(会通知虚拟机加载)
Modules.defineModule(null, base.descriptor(), baseUri);
Counters.add("jdk.module.boot.2.defineBaseTime", t2);
/*
* Step 2a:
*
* Scan all modules when --validate-modules specified
*/
/*
* 获取key为"jdk.module.validation"的系统属性的value，并将该条属性从系统属性集中移除。
* 注：被移除的属性可以去VM#savedProps中查找
*
* "jdk.module.validation"属性由"--validate-modules"映射而来
*
* --validate-modules用来指示对所有模块进行验证
*/
if(getAndRemoveProperty("jdk.module.validation") != null) {
int errors = ModulePathValidator.scanAllModules(System.out);
if(errors>0) {
fail("Validation of module path failed");
}
}
/*
* Step 3:
*
* If resolution is needed then create the module finder and the set of root modules to resolve.
*/
long t3 = System.nanoTime();
ModuleFinder savedModuleFinder = null;
ModuleFinder finder;
/*
* 模块系统解析的根模块，需要从此处解析模块依赖信息，最终形成完整的依赖图。
*
* 可以通过--add-modules将默认根模块之外的模块添加到模块依赖解析中。
* JDK9默认的root module是java.se模块。
*
* 由于java.se.ee不在默认的root modules中，
* 因此--add-modules的最常见的用途是用来添加ee中的模块，比如java.xml.bind
*/
Set<String> roots;
// 进行后续处理
if(needResolution) {
/*
* upgraded modules override the modules in the run-time image
*
* 存在"--upgrade-module-path"模块
*/
if(upgradeModulePath != null) {
// 组合upgradeModulePath和systemModuleFinder两个模块查找器
systemModuleFinder = ModuleFinder.compose(upgradeModulePath, systemModuleFinder);
}
/*
* The module finder: [--upgrade-module-path] system [--module-path]
*
* 存在"--module-path"模块
*/
if(appModulePath != null) {
// 组合systemModuleFinder和appModulePath两个模块查找器
finder = ModuleFinder.compose(systemModuleFinder, appModulePath);
// 如果不存在"--module-path"模块，直接使用上面的systemModuleFinde
} else {
finder = systemModuleFinder;
}
// The root modules to resolve
roots = new HashSet<>();
// launcher -m option to specify the main/initial module
if(mainModule != null) {
// 将主模块信息加入到根模块集合
roots.add(mainModule);
}
// additional module(s) specified by --add-modules
boolean addAllDefaultModules = false; // 是否添加未命名模块对应的根模块集合
boolean addAllSystemModules = false; // 是否添加所有的系统模块
boolean addAllApplicationModules = false; // 是否添加模块路径中搜索到的全部可见模块
for(String mod : addModules) {
switch(mod) {
case ALL_DEFAULT:
addAllDefaultModules = true;
break;
case ALL_SYSTEM:
addAllSystemModules = true;
break;
case ALL_MODULE_PATH:
addAllApplicationModules = true;
break;
default:
// 直接添加
roots.add(mod);
}
}
// 记录应用"--limit-modules"前的模块查找器
savedModuleFinder = finder;
// 如果存在"--limit-modules"信息
if(!limitModules.isEmpty()) {
finder = limitFinder(finder, limitModules, roots);
}
/*
* If there is no initial module specified then assume that the initial module is the unnamed module of the application class loader.
* This is implemented by resolving all observable modules that export an API.
* Modules that have the DO_NOT_RESOLVE_BY_DEFAULT bit set in their ModuleResolution attribute flags are excluded from the default set of roots
*/
if(mainModule == null || addAllDefaultModules) {
Set<String> finderSet = DefaultRoots.compute(systemModuleFinder, finder);
roots.addAll(finderSet);
}
// If `--add-modules ALL-SYSTEM` is specified then all observable system modules will be resolved.
if(addAllSystemModules) {
ModuleFinder f = finder; // observable modules
systemModuleFinder.findAll().stream().map(ModuleReference::descriptor).map(ModuleDescriptor::name).filter(mn -> f.find(mn).isPresent()) // observable
.forEach(mn -> roots.add(mn));
}
// If `--add-modules ALL-MODULE-PATH` is specified then all observable modules on the application module path will be resolved.
if(appModulePath != null && addAllApplicationModules) {
ModuleFinder f = finder; // observable modules
appModulePath.findAll().stream().map(ModuleReference::descriptor).map(ModuleDescriptor::name).filter(mn -> f.find(mn).isPresent()) // observable
.forEach(mn -> roots.add(mn));
}
} else {
// no resolution case
finder = systemModuleFinder;
roots = null;
}
Counters.add("jdk.module.boot.3.optionsAndRootsTime", t3);
/*
* Step 4:
*
* Resolve the root modules, with service binding, to create the configuration for the boot layer.
* If resolution is not needed then create the configuration for the boot layer from the readability graph created at link time.
*/
long t4 = System.nanoTime();
// 构造Boot Layer层的模块图
Configuration configuration;
if(needResolution) {
// 基于给定的待解析模块roots来构造模块依赖图(需要解析服务依赖)，父模块依赖图为空集
configuration = JLMA.resolveAndBind(finder, roots, traceOutput);
} else {
// 获取系统模块依赖(requires)映射
Map<String, Set<String>> map = systemModules.moduleReads();
// 由指定的模块依赖集构造模块依赖图，父模块图为空集
configuration = JLMA.newConfiguration(systemModuleFinder, map);
}
/* check that modules specified to --patch-module are resolved */
// 打印patch module信息
if(isPatched) {
patcher.patchedModules().stream().filter(mn -> !configuration.findModule(mn).isPresent()).forEach(mn -> warnUnknownModule(PATCH_MODULE, mn));
}
Counters.add("jdk.module.boot.4.resolveTime", t4);
/*
* Step 5:
*
* Map the modules in the configuration to class loaders.
* The static configuration provides the mapping of standard and JDK modules to the boot and platform loaders.
* All other modules (JDK tool modules, and both explicit and automatic modules on the application module path)
* are defined to the application class loader.
*/
long t5 = System.nanoTime();
/*
* mapping of modules to class loaders
*
* 将模块图中的module映射到PlatformClassLoader和AppClassLoader（过滤了BootClassLoader）
*/
Function<String, ClassLoader> mappingFunction = ModuleLoaderMap.mappingFunction(configuration);
// check that all modules to be mapped to the boot loader will be loaded from the runtime image
if(haveModulePath) {
for(ResolvedModule resolvedModule : configuration.modules()) {
ModuleReference mref = resolvedModule.reference();
String name = mref.descriptor().name();
ClassLoader cl = mappingFunction.apply(name);
if(cl == null) {
if(upgradeModulePath != null && upgradeModulePath.find(name).isPresent()) {
fail(name + ": cannot be loaded from upgrade module path");
}
if(!systemModuleFinder.find(name).isPresent()) {
fail(name + ": cannot be loaded from application module path");
}
}
}
}
// check for split packages in the modules mapped to the built-in loaders
if(systemModules.hasSplitPackages() || isPatched || haveModulePath) {
checkSplitPackages(configuration, mappingFunction);
}
// 将加载的模块信息注册到内置的类加载器中
loadModules(configuration, mappingFunction); // load/register the modules with the built-in class loaders
Counters.add("jdk.module.boot.5.loadModulesTime", t5);
/*
* Step 6:
*
* Define all modules to the VM
*/
long t6 = System.nanoTime();
// 构造一个空的模块层
ModuleLayer emptyLayer = ModuleLayer.empty();
// 用空模块层作为Boot Layer的父模块层，并基于上面创建的模块图来构造Boot Layer
ModuleLayer bootLayer = emptyLayer.defineModules(configuration, mappingFunction);
Counters.add("jdk.module.boot.6.layerCreateTime", t6);
/*
* Step 7:
*
* Miscellaneous
*/
// check incubating status
if(systemModules.hasIncubatorModules() || haveModulePath) {
checkIncubatingStatus(configuration);
}
// --add-reads, --add-exports/--add-opens, and --illegal-access
long t7 = System.nanoTime();
// 解析--add-reads选项
addExtraReads(bootLayer);
// 解析--add-exports和--add-opens选项
boolean extraExportsOrOpens = addExtraExportsAndOpens(bootLayer);
// 解析--illegal-access选项
addIllegalAccess(upgradeModulePath, systemModules, bootLayer, extraExportsOrOpens);
Counters.add("jdk.module.boot.7.adjustModulesTime", t7);
// save module finders for later use
if(savedModuleFinder != null) {
unlimitedFinder = new SafeModuleFinder(savedModuleFinder);
if(savedModuleFinder != finder) {
limitedFinder = new SafeModuleFinder(finder);
}
}
// total time to initialize
Counters.add("jdk.module.boot.totalTime", t0);
Counters.publish();
return bootLayer;
}
/**
* Initialize the module patcher for the initial configuration passed on the value of the --patch-module options.
*/
// 解析--patch-module信息，"--patch-module"名称在系统内部被转换为"jdk.module.patch.{序号}"
private static ModulePatcher initModulePatcher() {
Map<String, List<String>> map = decode("jdk.module.patch.", File.pathSeparator, false);
return new ModulePatcher(map);
}
/**
* Creates a finder from the module path that is the value of the given system property and optionally patched by --patch-module
*/
// 返回指定的属性对应的模块查找器
private static ModuleFinder finderFor(String prop) {
// 获取prop对应的系统属性的值。如果prop不存在，返回null
String s = System.getProperty(prop);
if(s == null) {
return null;
}
String[] dirs = s.split(File.pathSeparator);
Path[] paths = new Path[dirs.length];
int i = 0;
for(String dir : dirs) {
paths[i++] = Path.of(dir);
}
return ModulePath.of(patcher, paths);
}
/**
* Returns the set of module names specified by --add-module options.
*/
// 获取"--add-module"信息
private static Set<String> addModules() {
String prefix = "jdk.module.addmods.";
int index = 0;
/*
* 获取key为"jdk.module.addmods.{序号}"的系统属性的value，并将该条属性从系统属性集中移除。
* 注：被移除的属性可以去VM#savedProps中查找
*
* "jdk.module.addmods.{序号}"属性由"--add-module"映射而来
*/
String value = getAndRemoveProperty(prefix + index);
if(value == null) {
return Collections.emptySet();
}
Set<String> modules = new HashSet<>();
while(value != null) {
for(String s : value.split(",")) {
if(s.length()>0) {
modules.add(s);
}
}
index++;
value = getAndRemoveProperty(prefix + index);
}
return modules;
}
/**
* Returns the set of module names specified by --limit-modules.
*/
// 获取"--limit-modules"信息
private static Set<String> limitModules() {
/*
* 获取key为"jdk.module.limitmods"的系统属性的value，并将该条属性从系统属性集中移除。
* 注：被移除的属性可以去VM#savedProps中查找
*
* "jdk.module.limitmods"属性由"--limit-modules"映射而来
*/
String value = getAndRemoveProperty("jdk.module.limitmods");
if(value == null) {
return Collections.emptySet();
}
Set<String> names = new HashSet<>();
for(String name : value.split(",")) {
if(name.length()>0) {
names.add(name);
}
}
return names;
}
/**
* Returns a ModuleFinder that limits observability to the given root modules,
* their transitive dependences, plus a set of other modules.
*/
// 返回一组由"--limit-modules"限定的模块查找器
private static ModuleFinder limitFinder(ModuleFinder finder, Set<String> roots, Set<String> otherMods) {
// resolve all root modules
Configuration cf = Configuration.empty().resolve(finder, ModuleFinder.of(), roots);
// module name -> reference
Map<String, ModuleReference> map = new HashMap<>();
// root modules and their transitive dependences
cf.modules().stream().map(ResolvedModule::reference).forEach(mref -> map.put(mref.descriptor().name(), mref));
// additional modules
otherMods.stream().map(finder::find).flatMap(Optional::stream).forEach(mref -> map.putIfAbsent(mref.descriptor().name(), mref));
// set of modules that are observable
Set<ModuleReference> mrefs = new HashSet<>(map.values());
return new ModuleFinder() {
@Override
public Optional<ModuleReference> find(String name) {
return Optional.ofNullable(map.get(name));
}
@Override
public Set<ModuleReference> findAll() {
return mrefs;
}
};
}
/**
* Checks for split packages between modules defined to the built-in class
* loaders.
*/
private static void checkSplitPackages(Configuration cf, Function<String, ClassLoader> clf) {
Map<String, String> packageToModule = new HashMap<>();
for(ResolvedModule resolvedModule : cf.modules()) {
ModuleDescriptor descriptor = resolvedModule.reference().descriptor();
String name = descriptor.name();
ClassLoader loader = clf.apply(name);
if(loader == null || loader instanceof BuiltinClassLoader) {
for(String p : descriptor.packages()) {
String other = packageToModule.putIfAbsent(p, name);
if(other != null) {
String msg = "Package " + p + " in both module " + name + " and module " + other;
throw new LayerInstantiationException(msg);
}
}
}
}
}
/**
* Load/register the modules to the built-in class loaders.
*/
// 将加载的模块信息注册到内置的类加载器中
private static void loadModules(Configuration cf, Function<String, ClassLoader> clf) {
for(ResolvedModule resolvedModule : cf.modules()) {
ModuleReference mref = resolvedModule.reference();
String name = resolvedModule.name();
ClassLoader loader = clf.apply(name);
if(loader == null) {
// skip java.base as it is already loaded
if(!name.equals(JAVA_BASE)) {
BootLoader.loadModule(mref);
}
} else if(loader instanceof BuiltinClassLoader) {
((BuiltinClassLoader) loader).loadModule(mref);
}
}
}
/**
* Checks incubating status of modules in the configuration
*/
private static void checkIncubatingStatus(Configuration cf) {
String incubating = null;
for(ResolvedModule resolvedModule : cf.modules()) {
ModuleReference mref = resolvedModule.reference();
// emit warning if the WARN_INCUBATING module resolution bit set
if(ModuleResolution.hasIncubatingWarning(mref)) {
String mn = mref.descriptor().name();
if(incubating == null) {
incubating = mn;
} else {
incubating += ", " + mn;
}
}
}
if(incubating != null) {
warn("Using incubator modules: " + incubating);
}
}
/**
* Process the --add-reads options to add any additional read edges that are specified on the command-line.
*/
// 解析--add-reads选项
private static void addExtraReads(ModuleLayer bootLayer) {
// 获取--add-opens信息，"--add-opens"名称在系统内部被转换为"jdk.module.addreads.{序号}"
Map<String, List<String>> map = decode("jdk.module.addreads.");
if(map.isEmpty()) {
return;
}
for(Map.Entry<String, List<String>> e : map.entrySet()) {
// the key is $MODULE
String mn = e.getKey();
// 在模块层bootLayer以及父模块层中查找指定名称的模块
Optional<Module> module = bootLayer.findModule(mn);
// 如果指定的模块不存在
if(module.isEmpty()) {
// 打印日志，提示无法识别当前模块
warnUnknownModule(ADD_READS, mn);
continue;
}
Module sourceModule = module.get();
// the value is the set of other modules (by name)
for(String name : e.getValue()) {
if(ALL_UNNAMED.equals(name)) {
// 使模块sourceModule依赖(requires)所有未命名模块，需要通知VM
Modules.addReadsAllUnnamed(sourceModule);
} else {
// 在模块层bootLayer以及父模块层中查找指定名称的模块
module = bootLayer.findModule(name);
if(module.isPresent()) {
// 使sourceModule模块依赖(requires)module模块
Modules.addReads(sourceModule, module.get());
} else {
warnUnknownModule(ADD_READS, name);
}
}
}
}
}
/**
* Process the --add-exports and --add-opens options to export/open
* additional packages specified on the command-line.
*/
// 解析--add-exports和--add-opens选项
private static boolean addExtraExportsAndOpens(ModuleLayer bootLayer) {
boolean extraExportsOrOpens = false;
// --add-exports，"--add-exports"名称在系统内部被转换为"jdk.module.addexports.{序号}"
String prefix = "jdk.module.addexports.";
// 获取--add-exports信息
Map<String, List<String>> extraExports = decode(prefix);
if(!extraExports.isEmpty()) {
addExtraExportsOrOpens(bootLayer, extraExports, false);
extraExportsOrOpens = true;
}
// --add-opens，"--add-opens"名称在系统内部被转换为"jdk.module.addopens.{序号}"
prefix = "jdk.module.addopens.";
// 获取--add-opens信息
Map<String, List<String>> extraOpens = decode(prefix);
if(!extraOpens.isEmpty()) {
addExtraExportsOrOpens(bootLayer, extraOpens, true);
extraExportsOrOpens = true;
}
return extraExportsOrOpens;
}
// 解析--add-exports和--add-opens选项
private static void addExtraExportsOrOpens(ModuleLayer bootLayer, Map<String, List<String>> map, boolean opens) {
String option = opens ? ADD_OPENS : ADD_EXPORTS;
for(Map.Entry<String, List<String>> e : map.entrySet()) {
// the key is $MODULE/$PACKAGE
String key = e.getKey();
String[] s = key.split("/");
if(s.length != 2) {
fail(unableToParse(option, "<module>/<package>", key));
}
String mn = s[0];
String pn = s[1];
if(mn.isEmpty() || pn.isEmpty()) {
fail(unableToParse(option, "<module>/<package>", key));
}
// The exporting module is in the boot layer
Module m;
Optional<Module> om = bootLayer.findModule(mn);
if(!om.isPresent()) {
warnUnknownModule(option, mn);
continue;
}
m = om.get();
if(!m.getDescriptor().packages().contains(pn)) {
warn("package " + pn + " not in " + mn);
continue;
}
// the value is the set of modules to export to (by name)
for(String name : e.getValue()) {
boolean allUnnamed = false;
Module other = null;
if(ALL_UNNAMED.equals(name)) {
allUnnamed = true;
} else {
om = bootLayer.findModule(name);
if(om.isPresent()) {
other = om.get();
} else {
warnUnknownModule(option, name);
continue;
}
}
if(allUnnamed) {
if(opens) {
Modules.addOpensToAllUnnamed(m, pn);
} else {
Modules.addExportsToAllUnnamed(m, pn);
}
} else {
if(opens) {
Modules.addOpens(m, pn, other);
} else {
Modules.addExports(m, pn, other);
}
}
}
}
}
/**
* Decodes the values of --add-reads, -add-exports or --add-opens which use the "," to separate the RHS of the option value.
*/
// 从系统属性中解析出--add-reads, -add-exports, --add-opens这类选项的映射信息
private static Map<String, List<String>> decode(String prefix) {
return decode(prefix, ",", true);
}
/**
* Decodes the values of --add-reads, -add-exports, --add-opens or --patch-modules options that are encoded in system properties.
*
* @param prefix the system property prefix
* @param regex the regex for splitting the RHS of the option value
*/
// 从系统属性中解析出--patch-modules, --add-reads, -add-exports, --add-opens这类选项的映射信息
private static Map<String, List<String>> decode(String prefix, String regex, boolean allowDuplicates) {
int index = 0;
/* the system property is removed after decoding */
/*
* 获取key为prefix+index的系统属性的value，并将该条属性从系统属性集中移除。
* 注：被移除的属性可以去VM#savedProps中查找
*/
String value = getAndRemoveProperty(prefix + index);
if(value == null) {
return Collections.emptyMap();
}
Map<String, List<String>> map = new HashMap<>();
while(value != null) {
int pos = value.indexOf('=');
// 不存在"="
if(pos == -1) {
fail(unableToParse(option(prefix), "<module>=<value>", value));
}
// 不存在<module>
if(pos == 0) {
fail(unableToParse(option(prefix), "<module>=<value>", value));
}
// key is <module> or <module>/<package>
String key = value.substring(0, pos); // "="之前的内容
String rhs = value.substring(pos + 1); // "="之后的内容，使用指定的分隔符来分割
if(rhs.isEmpty()) {
fail(unableToParse(option(prefix), "<module>=<value>", value));
}
// value is <module>(,<module>)* or <file>(<pathsep><file>)*
if(!allowDuplicates && map.containsKey(key)) {
fail(key + " specified more than once to " + option(prefix));
}
List<String> values = map.computeIfAbsent(key, k -> new ArrayList<>());
int ntargets = 0;
for(String s : rhs.split(regex)) {
if(s.length()>0) {
values.add(s);
ntargets++;
}
}
if(ntargets == 0) {
fail("Target must be specified: " + option(prefix) + " " + value);
}
index++;
value = getAndRemoveProperty(prefix + index);
}
return map;
}
/**
* Returns the command-line option name corresponds to the specified system property prefix.
*/
// 命令行参数与内部标识之间的转换
static String option(String prefix) {
switch(prefix) {
case "jdk.module.addexports.":
return ADD_EXPORTS;
case "jdk.module.addopens.":
return ADD_OPENS;
case "jdk.module.addreads.":
return ADD_READS;
case "jdk.module.patch.":
return PATCH_MODULE;
case "jdk.module.addmods.":
return ADD_MODULES;
default:
throw new IllegalArgumentException(prefix);
}
}
/**
* Process the --illegal-access option (and its default) to open packages
* of system modules in the boot layer to code in unnamed modules.
*/
// 解析--illegal-access选项(是否允许unnamed modules反射使用所有named modules中的类，为了方便迁移设置，将来可能会被移除)
private static void addIllegalAccess(ModuleFinder upgradeModulePath, SystemModules systemModules, ModuleLayer bootLayer, boolean extraExportsOrOpens) {
/*
* 获取key为"jdk.module.illegalAccess"的系统属性的value，并将该条属性从系统属性集中移除。
* 注：被移除的属性可以去VM#savedProps中查找
*
* "jdk.module.illegalAccess"属性由"--illegal-access"映射而来
*/
String value = getAndRemoveProperty("jdk.module.illegalAccess");
IllegalAccessLogger.Mode mode = IllegalAccessLogger.Mode.ONESHOT;
if(value != null) {
switch(value) {
case "deny":
return;
case "permit":
break;
case "warn":