比较两个字符串与开始时的汇编错误

Question

我正在为使用JSP的Google应用程序引擎进行开发。我需要通过String类中的startsWith（）方法比较两个字符串。

这是我正在处理的代码。

<% 
      String artist = "Surendra Perera"; 

      DatastoreService datastore = DatastoreServiceFactory.getDatastoreService(); 
      Key songKey = KeyFactory.createKey("songs", 123454); 
      // Run an ancestor query to ensure we see the most up-to-date 
      // view of the songs. 
      Query query = new Query("Song", songKey).addSort("Artist"); 
      //query.addFilter("Artist", Query.FilterOperator.IN, "Milton Mallawarachchi"); 
      List<Entity> songsList = datastore.prepare(query).asList(FetchOptions.Builder.withLimit(30)); 
      if(songsList.isEmpty()){ 
      %> 
      <p>There are no songs</p> 
      <% 
      }else{ 
%> 
<ul class="playlist"> 
<% 
      for(Entity song : songsList){ 
       if(artist.startsWith(song.getProperty("Artist"))){ 
%> 

<li><a href="<%= song.getProperty("Link") %>"><%= song.getProperty("Title") %>&#160;&#160;<span class="comment"><%= song.getProperty("Artist") %></span></a></li> 

<% }}} %> 

而且这里是我得到的错误....

HTTP ERROR 500 

Problem accessing /search.jsp. Reason: 
    Unable to compile class for JSP: 

An error occurred at line: -1 in the generated java file 
    [javac] C:\DOCUME~1\SILICO~1\LOCALS~1\Temp\Jetty_127_0_0_1_8888_war____.g0qk00\jsp\org\apache\jsp\search_jsp.java:178: cannot find symbol 
    [javac] symbol : method startsWith(java.lang.Object) 
    [javac] location: class java.lang.String 
    [javac]     if(artist.startsWith(song.getProperty("Artist"))){ 
    [javac]      ^
    [javac] 1 error 



Stacktrace: 

Caused by: 
org.apache.jasper.JasperException: Unable to compile class for JSP: 

An error occurred at line: -1 in the generated java file 
    [javac] C:\DOCUME~1\SILICO~1\LOCALS~1\Temp\Jetty_127_0_0_1_8888_war____.g0qk00\jsp\org\apache\jsp\search_jsp.java:178: cannot find symbol 
    [javac] symbol : method startsWith(java.lang.Object) 
    [javac] location: class java.lang.String 
    [javac]     if(artist.startsWith(song.getProperty("Artist"))){ 
    [javac]      ^
    [javac] 1 error 

提前感谢！

Answer 1

错误说明它无法在String类中找到给定方法method startsWith(java.lang.Object)。请注意，错误说java.lang.Object作为方法参数。这确实是错误的。它必须是java.lang.String，另请参阅javadoc。

你必须从Object到String改变song.getProperty()返回类型：

public String getProperty(String name) { 
    // ... 
} 

或者对(String)添加投如果是实际上String类型：

if (artist.startsWith((String) song.getProperty("Artist"))) { 
    // ... 
} 

或使用全功能Javabean：

public String getArtist() { 
    return artist; 
} 

与

if (artist.startsWith(song.getArtist())) { 
    // ... 
} 

最后但并非最不重要的，这个问题是无关到JSP。在普通的Java类中这样做会遇到完全相同的问题。在JSP文件中编写Java代码是not the best way以获得正确的基本概念。