Java -使用数组和流解析文件时未获得正确的项

hwamh0ep  于 2023-01-11  发布在  Java
关注(0)|答案(5)|浏览(82)

我尝试使用Java 1.8的流功能在macOS莫哈韦10.14.3操作系统上解析/etc/group文件。
我的/etc/group文件中的所有行如下所示：

nobody:*:-2:
nogroup:*:-1:
wheel:*:0:root
daemon:*:1:root
kmem:*:2:root
sys:*:3:root
tty:*:4:root
operator:*:5:root
mail:*:6:_teamsserver
bin:*:7:
procview:*:8:root
procmod:*:9:root
owner:*:10:
everyone:*:12:
_taskgated:*:13:_taskgated
group:*:16:
staff:*:20:root
_networkd:*:24:
_installassistant:*:25:
_lp:*:26:
_postfix:*:27:
_postdrop:*:28:
certusers:*:29:root,_jabber,_postfix,_cyrus,_calendar,_dovecot
_keytabusers:*:30:_calendar,_jabber,_postfix
_scsd:*:31:
_ces:*:32:
_appstore:*:33:_appstore
utmp:*:45:
authedusers:*:50:
interactusers:*:51:
netusers:*:52:
consoleusers:*:53:
_mcxalr:*:54:
_appleevents:*:55:
_geod:*:56:
_devdocs:*:59:
_sandbox:*:60:
localaccounts:*:61:
netaccounts:*:62:
_mdnsresponder:*:65:
_uucp:*:66:
_ard:*:67:
dialer:*:68:
network:*:69:
_www:*:70:_devicemgr,_teamsserver
_eppc:*:71:_eppc
_cvs:*:72:
_svn:*:73:
_mysql:*:74:
_sshd:*:75:
_qtss:*:76:
_mailman:*:78:
_appserverusr:*:79:
admin:*:80:root
_appserveradm:*:81:
_clamav:*:82:
_amavisd:*:83:
_jabber:*:84:
_appowner:*:87:
_windowserver:*:88:
_spotlight:*:89:
accessibility:*:90:
_tokend:*:91:
_securityagent:*:92:
_calendar:*:93:_teamsserver
_teamsserver:*:94:_devicemgr
_update_sharing:*:95:
_installer:*:96:
_atsserver:*:97:
_lpadmin:*:98:
_unknown:*:99:
_lpoperator:*:100:
_softwareupdate:*:200:_softwareupdate
_guest:*:201:
_coreaudiod:*:202:
_screensaver:*:203:
_developer:*:204:
_locationd:*:205:
_detachedsig:*:207:_locationd
_trustevaluationagent:*:208:
_odchpass:*:209:_teamsserver
_timezone:*:210:
_lda:*:211:
_cvms:*:212:
_usbmuxd:*:213:
_postgres:*:216:_devicemgr,_calendar,_teamsserver,_xserverdocs
_devicemgr:*:220:
_webauthserver:*:221:_teamsserver,_devicemgr
_netbios:*:222:
_warmd:*:224:_warmd
_dovenull:*:227:
_netstatistics:*:228:
_assetcache:*:235:
_coremediaiod:*:236:
_launchservicesd:*:239:
_iconservices:*:240:
_distnote:*:241:
_nsurlsessiond:*:242:
_nsurlstoraged:*:243:
_displaypolicyd:*:244:
_astris:*:245:
_gamecontrollerd:*:247:
_mbsetupuser:*:248:
_ondemand:*:249:
_analyticsusers:*:250:_analyticsd,_networkd,_timed,_reportmemoryexception
_xserverdocs:*:251:
_wwwproxy:*:252:
_mobileasset:*:253:
_findmydevice:*:254:
_datadetectors:*:257:
_captiveagent:*:258:
_ctkd:*:259:
_applepay:*:260:
_hidd:*:261:
_cmiodalassistants:*:262:
_analyticsd:*:263:_analyticsd
_webdeveloper:*:264:
_fpsd:*:265:_fpsd
_timed:*:266:
_reportmemoryexception:*:269:_reportmemoryexception
com.apple.access_ftp:*:395:
com.apple.access_disabled:*:396:
com.apple.access_sessionkey:*:397:
com.apple.access_screensharing:*:398:
com.apple.access_ssh:*:399:

Group.java:

public class Group {
    private String gid;
    private String name;
    private String members;

    public Group(String line) {
        String[] items = line.split(":");

        if (items.length <= 3) {
            this.name = items[0];
            System.out.print("Name: " + name + ", ");
            this.gid = items[2];
            System.out.print(" gid: " + gid + ", ");
        }
        else if (items.length >=3 || this.name != null || "".equals(this.name)){
            this.members = items[3];
            System.out.println("Members: " + members);
        }
    }

    // Omitted getters & setters for brevity

}

已创建此GroupsParser：

public class GroupParser {

    public static List<Group> getAllGroups(String line) {
        List<Group> groups = null;
        try (Stream<String> stream = Files.lines(Paths.get(line))) {

            groups = stream.filter(s -> s.charAt(0) != '#').map(Group::new)
                     .collect(Collectors.toCollection(ArrayList::new));
        } 
        catch (Exception e) {
            e.printStackTrace();
        }
        return groups;
    }

    public static void main(String[] args) {
        List<Group> groups = GroupParser.getAllGroups("/etc/group");
        for (Group group : groups) {
            System.out.println("Group: " + group.getName() + ", gid: " + group.getGid() + ", members: " + group.getMembers());
        }
    }
}

收到以下输出（显然顺序不对，缺少一些项）：

Group: nobody, gid: -2, members: null
Group: nogroup, gid: -1, members: null
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: _teamsserver
Group: bin, gid: 7, members: null
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: owner, gid: 10, members: null
Group: everyone, gid: 12, members: null
Group: null, gid: null, members: _taskgated
Group: group, gid: 16, members: null
Group: null, gid: null, members: root
Group: _networkd, gid: 24, members: null
Group: _installassistant, gid: 25, members: null
Group: _lp, gid: 26, members: null
Group: _postfix, gid: 27, members: null
Group: _postdrop, gid: 28, members: null
Group: null, gid: null, members: root,_jabber,_postfix,_cyrus,_calendar,_dovecot
Group: null, gid: null, members: _calendar,_jabber,_postfix
Group: _scsd, gid: 31, members: null
Group: _ces, gid: 32, members: null
Group: null, gid: null, members: _appstore
Group: utmp, gid: 45, members: null
Group: authedusers, gid: 50, members: null
Group: interactusers, gid: 51, members: null
Group: netusers, gid: 52, members: null
Group: consoleusers, gid: 53, members: null
Group: _mcxalr, gid: 54, members: null
Group: _appleevents, gid: 55, members: null
Group: _geod, gid: 56, members: null
Group: _devdocs, gid: 59, members: null
Group: _sandbox, gid: 60, members: null
Group: localaccounts, gid: 61, members: null
Group: netaccounts, gid: 62, members: null
Group: _mdnsresponder, gid: 65, members: null
Group: _uucp, gid: 66, members: null
Group: _ard, gid: 67, members: null
Group: dialer, gid: 68, members: null
Group: network, gid: 69, members: null
Group: null, gid: null, members: _devicemgr,_teamsserver
Group: null, gid: null, members: _eppc
Group: _cvs, gid: 72, members: null
Group: _svn, gid: 73, members: null
Group: _mysql, gid: 74, members: null
Group: _sshd, gid: 75, members: null
Group: _qtss, gid: 76, members: null
Group: _mailman, gid: 78, members: null
Group: _appserverusr, gid: 79, members: null
Group: null, gid: null, members: root
Group: _appserveradm, gid: 81, members: null
Group: _clamav, gid: 82, members: null
Group: _amavisd, gid: 83, members: null
Group: _jabber, gid: 84, members: null
Group: _appowner, gid: 87, members: null
Group: _windowserver, gid: 88, members: null
Group: _spotlight, gid: 89, members: null
Group: accessibility, gid: 90, members: null
Group: _tokend, gid: 91, members: null
Group: _securityagent, gid: 92, members: null
Group: null, gid: null, members: _teamsserver
Group: null, gid: null, members: _devicemgr
Group: _update_sharing, gid: 95, members: null
Group: _installer, gid: 96, members: null
Group: _atsserver, gid: 97, members: null
Group: _lpadmin, gid: 98, members: null
Group: _unknown, gid: 99, members: null
Group: _lpoperator, gid: 100, members: null
Group: null, gid: null, members: _softwareupdate
Group: _guest, gid: 201, members: null
Group: _coreaudiod, gid: 202, members: null
Group: _screensaver, gid: 203, members: null
Group: _developer, gid: 204, members: null
Group: _locationd, gid: 205, members: null
Group: null, gid: null, members: _locationd
Group: _trustevaluationagent, gid: 208, members: null
Group: null, gid: null, members: _teamsserver
Group: _timezone, gid: 210, members: null
Group: _lda, gid: 211, members: null
Group: _cvms, gid: 212, members: null
Group: _usbmuxd, gid: 213, members: null
Group: null, gid: null, members: _devicemgr,_calendar,_teamsserver,_xserverdocs
Group: _devicemgr, gid: 220, members: null
Group: null, gid: null, members: _teamsserver,_devicemgr
Group: _netbios, gid: 222, members: null
Group: null, gid: null, members: _warmd
Group: _dovenull, gid: 227, members: null
Group: _netstatistics, gid: 228, members: null
Group: _assetcache, gid: 235, members: null
Group: _coremediaiod, gid: 236, members: null
Group: _launchservicesd, gid: 239, members: null
Group: _iconservices, gid: 240, members: null
Group: _distnote, gid: 241, members: null
Group: _nsurlsessiond, gid: 242, members: null
Group: _nsurlstoraged, gid: 243, members: null
Group: _displaypolicyd, gid: 244, members: null
Group: _astris, gid: 245, members: null
Group: _gamecontrollerd, gid: 247, members: null
Group: _mbsetupuser, gid: 248, members: null
Group: _ondemand, gid: 249, members: null
Group: null, gid: null, members: _analyticsd,_networkd,_timed,_reportmemoryexception
Group: _xserverdocs, gid: 251, members: null
Group: _wwwproxy, gid: 252, members: null
Group: _mobileasset, gid: 253, members: null
Group: _findmydevice, gid: 254, members: null
Group: _datadetectors, gid: 257, members: null
Group: _captiveagent, gid: 258, members: null
Group: _ctkd, gid: 259, members: null
Group: _applepay, gid: 260, members: null
Group: _hidd, gid: 261, members: null
Group: _cmiodalassistants, gid: 262, members: null
Group: null, gid: null, members: _analyticsd
Group: _webdeveloper, gid: 264, members: null
Group: null, gid: null, members: _fpsd
Group: _timed, gid: 266, members: null
Group: null, gid: null, members: _reportmemoryexception
Group: com.apple.access_ftp, gid: 395, members: null
Group: com.apple.access_disabled, gid: 396, members: null
Group: com.apple.access_sessionkey, gid: 397, members: null
Group: com.apple.access_screensharing, gid: 398, members: null
Group: com.apple.access_ssh, gid: 399, members: null
Group: nobody, gid: -2, members: null
Group: nogroup, gid: -1, members: null
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: null, gid: null, members: _teamsserver
Group: bin, gid: 7, members: null
Group: null, gid: null, members: root
Group: null, gid: null, members: root
Group: owner, gid: 10, members: null
Group: everyone, gid: 12, members: null
Group: null, gid: null, members: _taskgated
Group: group, gid: 16, members: null
Group: null, gid: null, members: root
Group: _networkd, gid: 24, members: null
Group: _installassistant, gid: 25, members: null
Group: _lp, gid: 26, members: null
Group: _postfix, gid: 27, members: null
Group: _postdrop, gid: 28, members: null
Group: null, gid: null, members: root,_jabber,_postfix,_cyrus,_calendar,_dovecot
Group: null, gid: null, members: _calendar,_jabber,_postfix
Group: _scsd, gid: 31, members: null
Group: _ces, gid: 32, members: null
Group: null, gid: null, members: _appstore
Group: utmp, gid: 45, members: null
Group: authedusers, gid: 50, members: null
Group: interactusers, gid: 51, members: null
Group: netusers, gid: 52, members: null
Group: consoleusers, gid: 53, members: null
Group: _mcxalr, gid: 54, members: null
Group: _appleevents, gid: 55, members: null
Group: _geod, gid: 56, members: null
Group: _devdocs, gid: 59, members: null
Group: _sandbox, gid: 60, members: null
Group: localaccounts, gid: 61, members: null
Group: netaccounts, gid: 62, members: null
Group: _mdnsresponder, gid: 65, members: null
Group: _uucp, gid: 66, members: null
Group: _ard, gid: 67, members: null
Group: dialer, gid: 68, members: null
Group: network, gid: 69, members: null
Group: null, gid: null, members: _devicemgr,_teamsserver
Group: null, gid: null, members: _eppc
Group: _cvs, gid: 72, members: null
Group: _svn, gid: 73, members: null
Group: _mysql, gid: 74, members: null
Group: _sshd, gid: 75, members: null
Group: _qtss, gid: 76, members: null
Group: _mailman, gid: 78, members: null
Group: _appserverusr, gid: 79, members: null
Group: null, gid: null, members: root
Group: _appserveradm, gid: 81, members: null
Group: _clamav, gid: 82, members: null
Group: _amavisd, gid: 83, members: null
Group: _jabber, gid: 84, members: null
Group: _appowner, gid: 87, members: null
Group: _windowserver, gid: 88, members: null
Group: _spotlight, gid: 89, members: null
Group: accessibility, gid: 90, members: null
Group: _tokend, gid: 91, members: null
Group: _securityagent, gid: 92, members: null
Group: null, gid: null, members: _teamsserver
Group: null, gid: null, members: _devicemgr
Group: _update_sharing, gid: 95, members: null
Group: _installer, gid: 96, members: null
Group: _atsserver, gid: 97, members: null
Group: _lpadmin, gid: 98, members: null
Group: _unknown, gid: 99, members: null
Group: _lpoperator, gid: 100, members: null
Group: null, gid: null, members: _softwareupdate
Group: _guest, gid: 201, members: null
Group: _coreaudiod, gid: 202, members: null
Group: _screensaver, gid: 203, members: null
Group: _developer, gid: 204, members: null
Group: _locationd, gid: 205, members: null
Group: null, gid: null, members: _locationd
Group: _trustevaluationagent, gid: 208, members: null
Group: null, gid: null, members: _teamsserver
Group: _timezone, gid: 210, members: null
Group: _lda, gid: 211, members: null
Group: _cvms, gid: 212, members: null
Group: _usbmuxd, gid: 213, members: null
Group: null, gid: null, members: _devicemgr,_calendar,_teamsserver,_xserverdocs
Group: _devicemgr, gid: 220, members: null
Group: null, gid: null, members: _teamsserver,_devicemgr
Group: _netbios, gid: 222, members: null
Group: null, gid: null, members: _warmd
Group: _dovenull, gid: 227, members: null
Group: _netstatistics, gid: 228, members: null
Group: _assetcache, gid: 235, members: null
Group: _coremediaiod, gid: 236, members: null
Group: _launchservicesd, gid: 239, members: null
Group: _iconservices, gid: 240, members: null
Group: _distnote, gid: 241, members: null
Group: _nsurlsessiond, gid: 242, members: null
Group: _nsurlstoraged, gid: 243, members: null
Group: _displaypolicyd, gid: 244, members: null
Group: _astris, gid: 245, members: null
Group: _gamecontrollerd, gid: 247, members: null
Group: _mbsetupuser, gid: 248, members: null
Group: _ondemand, gid: 249, members: null
Group: null, gid: null, members: _analyticsd,_networkd,_timed,_reportmemoryexception
Group: _xserverdocs, gid: 251, members: null
Group: _wwwproxy, gid: 252, members: null
Group: _mobileasset, gid: 253, members: null
Group: _findmydevice, gid: 254, members: null
Group: _datadetectors, gid: 257, members: null
Group: _captiveagent, gid: 258, members: null
Group: _ctkd, gid: 259, members: null
Group: _applepay, gid: 260, members: null
Group: _hidd, gid: 261, members: null
Group: _cmiodalassistants, gid: 262, members: null
Group: null, gid: null, members: _analyticsd
Group: _webdeveloper, gid: 264, members: null
Group: null, gid: null, members: _fpsd
Group: _timed, gid: 266, members: null
Group: null, gid: null, members: _reportmemoryexception
Group: com.apple.access_ftp, gid: 395, members: null
Group: com.apple.access_disabled, gid: 396, members: null
Group: com.apple.access_sessionkey, gid: 397, members: null
Group: com.apple.access_screensharing, gid: 398, members: null
Group: com.apple.access_ssh, gid: 399, members: null

问题：
1.此输出似乎未排序
组：nobody，gid：-2名，成员：零
组：无组，gid：-1，成员：零
为什么我会得到这个，在nogroup和wheel之间？
1.有没有更好的方法来提取这些项目？为什么我看不到kmem或wheel？
1.是否有办法通过流来检查/修复此问题？

Java

5条答案

按热度按时间
gopyfrb3

gopyfrb31#

问题的核心在于您在Map为**.map(Group::new)**时使用的构造函数。当前实现的构造函数的逻辑是出现一些问题的原因。尝试解释如下：

public Group(String line) {
    String[] items = line.split(":"); // you split up the string into contents based on ':' separator

在检查内容是否拆分为小于或等于3个部分的条件中，您还假设数组的大小至少为**3**，这是执行items[2]时要访问的数组。if条件将成功地允许您最终获得针对这种访问的AIOOBE。

if (items.length <= 3) {
        this.name = items[0];
        System.out.print("Name: " + name + ", ");
        this.gid = items[2];
        System.out.print(" gid: " + gid + ", ");
    }

当字符串的内容可以拆分成3个以上的部分时，您往往不会为Group初始化name，gid，因此您在输出中会得到这些**null**。

else {

        this.members = items[3];
        System.out.println("Members: " + members);
    }
}

有没有更好的方法来提取这些项目？为什么我看不到kmem或wheel？
与通过初始化来处理null值相关的部分已经解决了这个问题。
为了避免NPE，您可能希望将groups初始化为空列表;

List<Group> groups = new ArrayList<>();

基于当使用:分割时串将总是具有3个或更多分量的假设的更简单的实现可以是：

public Group(String line) {
    String[] items = line.split(":");
    this.name = items[0];
    this.gid = Integer.parseInt(items[2]);
    if (items.length > 3){
        this.members = items[3];
    }
}
赞(0）分享  回复(0）举报  2023-01-11
brjng4g3

brjng4g32#

不确定我是否正确理解了您的问题。您只想逐行解析文件，而不执行任何groupBy/merge操作？对于Google Guava中的Splitter或我的库abacus-common，items.length > 3是不必要的。下面是简单的示例解决方案：

Splitter splitter = Splitter.with(':').trim(true);
Splitter memSplitter = Splitter.with(',').trim(true).omitEmptyStrings(true);

ExceptionalStream.lines(new File("./tmp.txt")) // Or StreamEx.of(IOUtil.readLines(new File("./tmp.txt")))
    .filter(s -> s.charAt(0) != '#')
    .map(s -> splitter.splitToArray(s))
    // .map(a -> Tuple.of(a[0], a[2], memSplitter.splitToArray(a[3])))
    // TODO whatever you need/want.
    .forEach(group -> N.println(group));
赞(0）分享  回复(0）举报  2023-01-11
eyh26e7m

eyh26e7m3#

根据我的观察：
1.此输出似乎未排序
将代码ArrayList::new更改为LinkedList::new以保持顺序。
1.有没有更好的方法来提取这些项目？为什么我看不到kmem或wheel？
代码if (items.length <= 3) {是问题的根源，else case不会为members以外的字段赋值
3.有没有办法通过Streams检查/修复此问题？
我想修复已经完成了。更好的方法-永远都有。

赞(0）分享  回复(0）举报  2023-01-11
z8dt9xmd

z8dt9xmd4#

下面的代码将帮助您：

class Group {

  private String gid;

  private String name;

  private String members;

  public Group(String line) {
    String[] consolidated = line.split(":");
    if (consolidated != null && consolidated.length > 0) {
      this.name = doesIndexExists(consolidated, 0) ? consolidated[0] : "";
      this.gid = doesIndexExists(consolidated, 2) ? consolidated[2] : "";
      this.members = consolidated.length < 4 ? "" : doesIndexExists(consolidated, 3) ? consolidated[3] : "";
    }
  }

  public String getGid() {
    return gid;
  }

  public void setGid(String gid) {
    this.gid = gid;
  }

  public String getName() {
    return name;
  }

  public String getMembers() {
    return members;
  }

  public boolean doesIndexExists(String[] inputArray, int index) {
    return inputArray.length > index && inputArray[index] != null;
  }

  public void setName(String name) {
    this.name = name;
  }

  public void setMembers(String members) {
    this.members = members;
  }

  @Override
  public String toString() {
    return "Group [gid=" + gid + ", name=" + name + ", members=" + members + "]";
  }

}

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class GroupParser {

  public static final String FILE_PATH = "YOURFILEPATH";

  public static boolean isNotEmpty(String inputContent) {
    return (inputContent != null && !"".equalsIgnoreCase(inputContent));
  }

  public static List<Group> getAllGroups(String line) throws IOException {
    final List<Group> groupList = new ArrayList<>();
    Files.readAllLines(Paths.get(line)).stream()
        .filter(lineInstance -> isNotEmpty(lineInstance) && !lineInstance.startsWith("#")).collect(Collectors.toList())
        .forEach(parsedInputObject -> groupList.add(new Group(parsedInputObject)));
    return groupList;
  }

  public static void main(String[] args) throws IOException {
    List<Group> groups = GroupParser.getAllGroups(FILE_PATH);
    for (Group group : groups) {
      System.out.println("Group: " + group.getName() + ", gid: " + group.getGid() + ", members: " + group.getMembers());
    }
  }
}
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fdbelqdn

fdbelqdn5#

我可以建议一个比检查数组长度或引入额外库更简单的修复方法吗？只需添加几个分隔符，以保证数组项的数量充足：

String[] items = (line + "::::").split(":");

如果您希望代码紧凑，那么String.split(String, int)可以通过不解析超过您想要的列来保存一些可以忽略不计的时间。
好吧，就这样。

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