java好习惯2

1.这么拼参数的

学习一下，当keys.length-1是加上"&"而且是在拼串的后面

public static String map2Content(Map params){
  StringBuilder stringBuilder=new StringBuilder();
  try {
    Set keySet=params.keySet();
    Object[] keys=keySet.toArray();
    for (int i=0; i < keys.length; i++) {
      stringBuilder.append(encode(keys[i].toString(),"UTF-8")).append("=").append(encode(params.get(keys[i]).toString(),"UTF-8"));
      if (i < (keys.length - 1)) {
        stringBuilder.append("&");
      }
    }
  }
 catch (  Exception e) {
    throw new HttpException("failed to generate content from map",e);
  }
  return stringBuilder.toString();
}

2.如果文件存在就删除，再创建一个新文件

private void saveUsers(Set<String> set,String fileName){
  File f=new File(getDataFolder(),fileName);
  if (f.exists()) {
    f.delete();
  }
  try {
    f.createNewFile();
    BufferedWriter bWriter=new BufferedWriter(new FileWriter(f));
    int count=0;
    for (    String name : set) {
      bWriter.write(name + System.getProperty("line.separator"));
      count++;
    }
    ConsoleUtils.printInfo(NAME,"Saved " + count + " users in '"+ fileName+ "'!");
    bWriter.flush();
    bWriter.close();
  }
 catch (  Exception e) {
    ConsoleUtils.printException(e,NAME,"Error while saving file '" + fileName + "'!");
  }
}

3.if(widget instanceof Checkbox){

CheckBox cb = (Checkbox)widget如果是这个的实例，强转成这个类,常用的写法

}

@Override public Set<Activity> ge
tInstitutionActivities(){
  Set<Activity> activities=new HashSet<Activity>();
  for (int i=0; i < institutionActivities.getWidgetCount(); i++) {
    Widget widget=institutionActivities.getWidget(i);
    if (widget instanceof CheckBox) {
      CheckBox cb=(CheckBox)widget;
      if (cb.getValue()) {
        Activity activity=new Activity();
        activity.setId(Integer.parseInt(cb.getFormValue()));
        activity.setName(cb.getText());
        activities.add(activity);
      }
    }
  }
  return activities;
}

4.set中添加元素而且不重复

private Object createStringSet(String... strings){
  Set<String> stringSet=new HashSet<String>();
  for (  String string : strings) {
    stringSet.add(string);
  }
  return stringSet;
}

5.异常时可以返回null,为空可以返回null

public static String getSearchEngineQueryString(HttpServletRequest request,String referrer){
  String queryString=null;
  String hostName=null;
  if (referrer != null) {
    URL refererURL;
    try {
      refererURL=new URL(referrer);
    }
 catch (    MalformedURLException e) {
      return null;
    }
    hostName=refererURL.getHost();
    queryString=refererURL.getQuery();
    if (Strings.isEmpty(queryString)) {
      return null;
    }
    Set<String> keys=seParams.keySet();
    for (    String se : keys) {
      if (hostName.toLowerCase().contains(se)) {
        queryString=getQueryStringParameter(queryString,seParams.get(se));
      }
    }
    return queryString;
  }
  return null;
}

6.用Iterator遍历collection

@SuppressWarnings("rawtypes") public static String toReadableString(Collection collection){
  Iterator it=collection.iterator();
  StringBuilder strb=new StringBuilder();
  while (it.hasNext()) {
    Object next=it.next();
    strb.append(next.toString() + ", ");
  }
  if (strb.length() > 2) {
    strb.delete(strb.length() - 2,strb.length());
  }
  return strb.toString();
}

7.将JSON字符串变成map

public static Map<String,Object> parseJSON(String jsonBody) throws JSONException {
  Map<String,Object> params=new HashMap<String,Object>();
  JSONObject obj=new JSONObject(jsonBody);
  Iterator it=obj.keys();
  while (it.hasNext()) {
    Object o=it.next();
    if (o instanceof String) {
      String key=(String)o;
      params.put(key,obj.get(key));
    }
  }
  return params;
}

8.这样往param中设置参数，request.getParameter()

protected void copyParams(HttpParams target){
  Iterator iter=parameters.entrySet().iterator();
  while (iter.hasNext()) {
    Map.Entry me=(Map.Entry)iter.next();
    if (me.getKey() instanceof String)     target.setParameter((String)me.getKey(),me.getValue());
  }
}

9.jsonnode的遍历

private <T>List<T> deserializeList(JsonNode jsonNode,String postType,Class<T> type){
  JsonNode dataNode=jsonNode.get("data");
  List<T> posts=new ArrayList<T>();
  for (Iterator<JsonNode> iterator=dataNode.iterator(); iterator.hasNext(); ) {
    posts.add(deserializePost(postType,type,(ObjectNode)iterator.next()));
  }
  return posts;
}

10.遍历map

public static void writeOneToMany(final OutputStream sink,Map mapping) throws Exception {
  final StringBuilder out=new StringBuilder();
  if (mapping == null) {
    mapping=new HashMap();
  }
  final Iterator keyIter=mapping.keySet().iterator();
  while (keyIter.hasNext()) {
    final String name=(String)keyIter.next();
    out.append(name).append(" ");
    final Collection points=(Collection)mapping.get(name);
    final Iterator pointIter=points.iterator();
    while (pointIter.hasNext()) {
      final Point point=(Point)pointIter.next();
      out.append(" (").append(point.x).append(",").append(point.y).append(")");
      if (pointIter.hasNext())       out.append(" ");
    }
    if (keyIter.hasNext()) {
      out.append("
");
    }
  }
  write(out,sink);
}

11.Iterator这么写

public List<File> getFileList(){
  List<File> list=new ArrayList<File>();
  for (Iterator it=iterator(); it.hasNext(); ) {
    FileResource resource=(FileResource)it.next();
    File file=resource.getFile();
    list.add(file);
  }
  return list;
}

12.set.add(元素)set这么添加元素的

private Object createStringSet(String... strings){
  Set<String> stringSet=new HashSet<String>();
  for (  String string : strings) {
    stringSet.add(string);
  }
  return stringSet;
}

13.格式化日期

/** 
 * Creates a Calendar object based off a string with this format <Day name:3 letters>, DD <Month name: 3 letters> YYYY HH:MM:SS +0000
 * @param date - The string we are to convert to a calendar date
 * @return - The calendar date object that this string represents
 */
public static Calendar makeDate(String date){
  Date d=null;
  Calendar calendar=Calendar.getInstance();
  try {
    SimpleDateFormat format=new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss Z");
    d=format.parse(date);
    calendar.setTime(d);
  }
 catch (  ParseException e) {
    e.printStackTrace();
  }
  return calendar;
}

14.学习这种日期的返回方式

public Date getDate(){
  if (value == null) {
    return null;
  }
  if (value instanceof Date) {
    return (Date)value;
  }
  throw new DbException(String.format("%s is not a date",value.toString()));
}

15.为什么要这么判断呢？

public Date parse(final String source) throws ParseException {
  if (source == null) {
    throw new ParseException("source is null",0);
  }
  return formater.parse(source);
}

16.

public static String getSearchEngineQueryString(HttpServletRequest request,String referrer){
  String queryString=null;
  String hostName=null;
  if (referrer != null) {
    URL refererURL;
    try {
      refererURL=new URL(referrer);
    }
 catch (    MalformedURLException e) {
      return null;
    }
    hostName=refererURL.getHost();
    queryString=refererURL.getQuery();
    if (Strings.isEmpty(queryString)) {
      return null;
    }
    Set<String> keys=seParams.keySet();
    for (    String se : keys) {
      if (hostName.toLowerCase().contains(se)) {
        queryString=getQueryStringParameter(queryString,seParams.get(se));
      }
    }
    return queryString;
  }
  return null;
}

17.

/** 
 * Gets URL for base of path containing Finalizer.class.
 */
URL getBaseUrl() throws IOException {
  String finalizerPath=FINALIZER_CLASS_NAME.replace('.','/') + ".class";
  URL finalizerUrl=getClass().getClassLoader().getResource(finalizerPath);
  if (finalizerUrl == null) {
    throw new FileNotFoundException(finalizerPath);
  }
  String urlString=finalizerUrl.toString();
  if (!urlString.endsWith(finalizerPath)) {
    throw new IOException("Unsupported path style: " + urlString);
  }
  urlString=urlString.substring(0,urlString.length() - finalizerPath.length());
  return new URL(finalizerUrl,urlString);
}

18.catch时可以返回返回值类型的

/** 
 * Reads in data from the saved file.
 * @param context - Context that gives us some system access
 * @return - Returns the list of items that were saved; If there was problemwhen gathering this data, an empty list is returned
 */
@SuppressWarnings("unchecked") public static ArrayList<Article> readData(Context context){
  ArrayList<Article> oldList=new ArrayList<Article>();
  try {
    FileInputStream fileStream=context.openFileInput("articles");
    ObjectInputStream reader=new ObjectInputStream(fileStream);
    oldList=(ArrayList<Article>)reader.readObject();
    reader.close();
    fileStream.close();
    return oldList;
  }
 catch (  java.io.FileNotFoundException e) {
    return new ArrayList<Article>();
  }
catch (  IOException e) {
    Log.e("AARSS","Problem loading the file. Does it exists?",e);
    return new ArrayList<Article>();
  }
catch (  ClassNotFoundException e) {
    Log.e("AARSS","Problem converting data from file.",e);
    return new ArrayList<Article>();
  }
}

19.在finally中关闭输入流

public static void read(Properties props,File file) throws IOException {
  FileInputStream fis=null;
  try {
    fis=new FileInputStream(file);
    props.load(fis);
  }
  finally {
    close(fis);
  }
}

20.