JDK 9 REPL：入门

会议是聚会Java名人的好地方。 Devoxx France是与Java语言架构师，前同事和老朋友Brian Goetz（ @briangoetz ）见面的一个机会。我们谈论了JDK 9，而他全都热衷于REPL。他提到，尽管Java SE 9中有很多重要功能，例如模块化和HTTP2客户端，但该工具将是最常被谈论的。该声明之所以有意义，是因为它将真正简化Java API的探索，原型开发，会议演示以及类似任务。该博客来自我们在那里的讨论以及他对REPL的强烈投票！

Read-Evaluate-Print-Loop在Lisp，Python，Ruby，Groovy，Clojure和其他语言中已经存在了一段时间。 Unix shell是一个REPL，它可以读取shell命令，评估它们，打印输出并返回循环以执行相同的操作。

jdk9-repl

您可以在JEP 222的 JDK 9中阅读有关REPL的全部信息。 JEP的摘要是：

提供一个交互式工具，用于评估Java编程语言的声明，语句和表达式：即，提供Java编程语言的读取-评估-打印循环（REPL）。另外，提供构建工具的API，使外部工具可以提供此功能。杰普222

JEP中也明确阐明了动机：

没有Foo类{public static void main（String [] args）{…}}的仪式，学习和探索就变得简化了。杰普222

JEP 222的目标是将REPL与JDK 9一起提供，但是openjdk.java.net/projects/jdk9并未将其列为“目标”或“建议目标”。好像是一个文档错误:)

从JDK 9 build 61开始，REPL未集成，需要单独构建。最终，在发布JDK 9之前的某个时间，此工具将集成到内部版本中。

让我们看看在OSX上运行它需要什么。该博客遵循Java 9 REPL –入门指南来构建和运行REPL。另外，它提供了命令的完整日志输出，这可能对某些人有用。

让我们开始吧！

安装JDK 9

在撰写本文时，下载最新的版本 61。
将JAVA_HOME设置为：
```
export JAVA_HOME=`/usr/libexec/java_home -v1.9`
```
在OSX上设置JAVA_HOME的更多详细信息在这里。

验证版本：

~> java -version
java version "1.9.0-ea"
Java(TM) SE Runtime Environment (build 1.9.0-ea-b61)
Java HotSpot(TM) 64-Bit Server VM (build 1.9.0-ea-b61, mixed mode)

检出并安装jline2

jline2是一个用于处理控制台输入的Java库。一探究竟：

workspaces> git clone git://github.com/jline/jline2.git
Cloning into 'jline2'...
remote: Counting objects: 6419, done.
remote: Total 6419 (delta 0), reused 0 (delta 0), pack-reused 6419
Receiving objects: 100% (6419/6419), 3.23 MiB | 80.00 KiB/s, done.
Resolving deltas: 100% (2945/2945), done.
Checking connectivity... done.

然后构建它：

jline2> mvn install
[INFO] Scanning for projects...
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/scm/maven-scm-provider-gitexe/1.8.1/maven-scm-provider-gitexe-1.8.1.pom
Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/scm/maven-scm-provider-gitexe/1.8.1/maven-scm-provider-gitexe-1.8.1.pom (3 KB at 0.3 KB/sec). . .[INFO] Installing /Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT-sources.jar to /Users/arungupta/.m2/repository/jline/jline/2.13-SNAPSHOT/jline-2.13-SNAPSHOT-sources.jar
[INFO] Installing /Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT-tests.jar to /Users/arungupta/.m2/repository/jline/jline/2.13-SNAPSHOT/jline-2.13-SNAPSHOT-tests.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 09:52 min
[INFO] Finished at: 2015-05-06T19:23:14-07:00
[INFO] Final Memory: 25M/146M
[INFO] ------------------------------------------------------------------------

克隆并构建JDK 9 REPL

该项目的OpenJDK代号为Kulla，意为“建设者之神”。该工具的计划名称为jshell 。

签出工作区：

workspaces> hg clone http://hg.openjdk.java.net/kulla/dev kulla
requesting all changes
adding changesets
adding manifests
adding file changes
added 1453 changesets with 2226 changes to 172 files
updating to branch default
109 files updated, 0 files merged, 0 files removed, 0 files unresolved

获取来源：

workspaces> cd kulla
kulla> chmod +x ./get_source.sh 
kulla> ./get_source.sh 
# Repositories:  corba jaxp jaxws langtools jdk hotspot nashorn corba:   hg clone http://hg.openjdk.java.net/kulla/dev/corba corbajaxp:   hg clone http://hg.openjdk.java.net/kulla/dev/jaxp jaxpcorba:   requesting all changesjaxp:   requesting all changescorba:   adding changesetsjaxp:   adding changesetscorba:   adding manifestsjaxp:   adding manifestscorba:   adding file changesjaxp:   adding file changescorba:   added 669 changesets with 4913 changes to 2576 filescorba:   updating to branch defaultcorba:   1184 files updated, 0 files merged, 0 files removed, 0 files unresolvedjaxws:   hg clone http://hg.openjdk.java.net/kulla/dev/jaxws jaxwsjaxws:   requesting all changesjaxws:   adding changesetsjaxws:   adding manifestsjaxws:   adding file changesjaxp:   added 728 changesets with 10192 changes to 7393 filesjaxp:   updating to branch defaultjaxp:   3044 files updated, 0 files merged, 0 files removed, 0 files unresolvedlangtools:   hg clone http://hg.openjdk.java.net/kulla/dev/langtools langtoolslangtools:   requesting all changeslangtools:   adding changesetslangtools:   adding manifestsjaxws:   added 589 changesets with 20521 changes to 10746 filesjaxws:   updating to branch defaultjaxws:   3750 files updated, 0 files merged, 0 files removed, 0 files unresolvedjdk:   hg clone http://hg.openjdk.java.net/kulla/dev/jdk jdklangtools:   adding file changesjdk:   requesting all changesjdk:   adding changesetsjdk:   adding manifestslangtools:   added 3173 changesets with 28112 changes to 9103 fileslangtools:   updating to branch defaultlangtools:   7100 files updated, 0 files merged, 0 files removed, 0 files unresolvedhotspot:   hg clone http://hg.openjdk.java.net/kulla/dev/hotspot hotspothotspot:   requesting all changeshotspot:   adding changesetshotspot:   adding manifestshotspot:   adding file changeshotspot:   added 8073 changesets with 45889 changes to 6290 fileshotspot:   updating to branch defaulthotspot:   5030 files updated, 0 files merged, 0 files removed, 0 files unresolvednashorn:   hg clone http://hg.openjdk.java.net/kulla/dev/nashorn nashornnashorn:   requesting all changesnashorn:   adding changesetsnashorn:   adding manifestsjdk:   adding file changesnashorn:   adding file changesnashorn:   added 1252 changesets with 11596 changes to 3595 filesnashorn:   updating to branch defaultnashorn:   2867 files updated, 0 files merged, 0 files removed, 0 files unresolvedjdk:   added 11805 changesets with 116593 changes to 42135 filesjdk:   updating to branch defaultjdk:   23192 files updated, 0 files merged, 0 files removed, 0 files unresolved
# Repositories:  . corba jaxp jaxws langtools jdk hotspot nashorn .:   cd . && hg pull -ucorba:   cd corba && hg pull -ujaxp:   cd jaxp && hg pull -ujaxws:   cd jaxws && hg pull -ulangtools:   cd langtools && hg pull -ujdk:   cd jdk && hg pull -uhotspot:   cd hotspot && hg pull -unashorn:   cd nashorn && hg pull -ujaxws:   pulling from http://hg.openjdk.java.net/kulla/dev/jaxwscorba:   pulling from http://hg.openjdk.java.net/kulla/dev/corbalangtools:   pulling from http://hg.openjdk.java.net/kulla/dev/langtoolshotspot:   pulling from http://hg.openjdk.java.net/kulla/dev/hotspotjdk:   pulling from http://hg.openjdk.java.net/kulla/dev/jdk.:   pulling from http://hg.openjdk.java.net/kulla/devjaxp:   pulling from http://hg.openjdk.java.net/kulla/dev/jaxpnashorn:   pulling from http://hg.openjdk.java.net/kulla/dev/nashornnashorn:   searching for changesnashorn:   no changes foundjaxws:   searching for changesjaxws:   no changes foundjaxp:   searching for changesjaxp:   no changes foundcorba:   searching for changescorba:   no changes foundjdk:   searching for changeshotspot:   searching for changeshotspot:   no changes foundjdk:   no changes found.:   searching for changes.:   no changes foundlangtools:   searching for changeslangtools:   no changes found

编辑langtools/repl/scripts/compile.sh脚本，如下所示：

#!/bin/sh
JLINE2LIB=/Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT.jar
mkdir -p build
javac -Xlint:unchecked -Xdiags:verbose -cp ${JLINE2LIB} -d build ../src/jdk.jshell/share/classes/*/*/*.java ../src/jdk.jshell/share/classes/*/*/*/*/*.java ../src/jdk.jshell/share/classes/*/*/*/*/*/*.java

注意，对于OSX，唯一的编辑是#!/bin/sh ，并将JLINE2LIB添加到先前编译的jline2工作区的位置。从引用JDK 9的JAVA_HOME中拾取javac 。

通过从langtools/repl目录调用脚本来编译REPL工具：
```
repl> chmod +x ./scripts/compile.sh
repl> ./scripts/compile.sh
```

运行JDK 9 REPL

编辑langtools/repl/scripts/run.sh脚本，如下所示：

#!/bin/sh
JLINE2LIB=/Users/arungupta/workspaces/jline2/target/jline-2.13-SNAPSHOT.jar
java -ea -esa -cp build:${JLINE2LIB} jdk.internal.jshell.tool.JShellTool "$@"

注意，唯一的编辑是OSX的!/bin/sh并添加JLINE2LIB 。

将REPL运行为：

repl> ./scripts/run.sh 
|  Welcome to JShell -- Version 0.428
|  Type /help for help

JDK 9 REPL Hello World

与引入Java的弹跳球或跳舞Duke引入不同，我们只将常规的Hello World用于REPL

将“ Hello World”运行为：

-> System.out.println("Hello World");
Hello World

瞧！

没有public static void main ，没有类的创建，没有仪式，只是干净而简单的Java代码。输入的文本称为“代码段”。

使用/list all可以查看完整的Java代码，如下所示：

-> /list all1 : import java.util.*;2 : import java.io.*;3 : import java.math.*;4 : import java.net.*;5 : import java.util.concurrent.*;6 : import java.util.prefs.*;7 : import java.util.regex.*;8 : void printf(String format, Object... args) { System.out.printf(format, args); }9 : System.out.println("Hello World");

此代码段可以另存为文件：

-> /save test

请注意，这不是Java文件。保存的代码段正是输入的内容：

repl> more test
System.out.println("Hello World");

该工具可以退出为：

-> /exit
|  Goodbye

或者您可以按Ctrl + C。

完整的命令列表很容易看到：

-> /help
Type a Java language expression, statement, or declaration.
Or type one of the following commands:/l  or /list [all]                -- list the source you have typed/seteditor <executable>    -- set the external editor command to use
/e  or /edit <name or id>         -- edit a source entry referenced by name or id
/-  or /drop <name or id>         -- delete a source entry referenced by name or id
/s  or /save [all|history] <file> -- save the source you have typed
/o  or /open <file>               -- open a file as source input
/v  or /vars                      -- list the declared variables and their values
/m  or /methods                   -- list the declared methods and their signatures
/c  or /classes                   -- list the declared classes
/x  or /exit                      -- exit the REPL
/r  or /reset                     -- reset everything in the REPL
/f  or /feedback <level>          -- feedback information: off, concise, normal, verbose, default, or ?
/p  or /prompt                    -- toggle display of a prompt
/cp or /classpath <path>          -- add a path to the classpath
/h  or /history                   -- history of what you have typed/setstart <file>           -- read file and set as the new start-up definitions/savestart <file>          -- save the default start-up definitions to the file
/?  or /help                      -- this help messageSupported shortcuts include:
<tab>       -- show possible completions for the current text
Shift-<tab> -- for current method or constructor invocation, show a synopsis of the method/constructor