Question

我正在使用JSP开发谷歌应用引擎。我需要通过String类中的startsWith（）方法比较两个字符串。

以下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>

<% }}} %>

这是我得到的错误......

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

提前致谢！

Answer 1

错误告诉它无法在method startsWith(java.lang.Object)类中找到给定的方法String。请注意，错误显示java.lang.Object作为方法参数。这确实是错的。它必须是java.lang.String，另请参阅javadoc。

您必须将song.getProperty()的返回类型从Object更改为String：

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

或在(String)上添加强制转型，如果它是{em>实际的String类型：

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

或使用值得信赖的Javabean：

public String getArtist() {
    return artist;
}

与

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

最后但同样重要的是，此问题与JSP 无关。在普通的Java类中执行此操作时，您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，以使基本概念正确。

使用startsWith比较两个字符串时的编译错误

1 个答案: