How to remove last character string in java

Just use the new java 8 StringJoiner! (And other nifty Java methods)

Example:

StringJoiner joiner = new StringJoiner(",");
joiner.add("foo");
joiner.add("bar");
joiner.add("baz");
String joined = joiner.toString(); // "foo,bar,baz"

It also supports streams in the form of Collectors.joining(",")

Full example:

public static void main(String[] args) {

    String input = "1\tJames\n2\tRichard";
    String output =  Arrays.stream(input.split("\n"))
                        .map( i -> String.format("{ id: \"%s\", name: \"%s\" }", i.split("\t")))
                        .collect(Collectors.joining(","));

    //prints: { id: "1", name: "James" },{ id: "2", name: "Richard" }       
    System.out.println(output);

}

You can avoid appending it in the first place :

for (int i=0; i<allLines.size(); i++){
     StringBuilder temp2 = new StringBuilder();

     String[] abc = line.split("\t");

     temp2.append("{");
     temp2.append("id: \""+abc[0]+"\",");
     temp2.append("name: \""+abc[1]+"\",");
     temp2.append("}");
     if (i<allLines.size()-1)
         temp2.append(",");
     temp.append(temp2.toString()); 

}

Alternatively add this after your for loop

    temp.setLength(temp.length() - 1);

which requires no constant index checking in your code

You can use deleteCharAt() method.

 StringBuilder s = new StringBuilder("{id: \"1\", name: \"Jhames\"},{id: \"2\", name: \"Richard\"},");
 System.out.println(s.deleteCharAt(s.lastIndexOf(",")));

First of all you don't need two StringBuilders, so instead of

StringBuilder sb1 = ..
for(..){
    StringBuilder sb2 = ...
    //fill sb2
    sb1.append(sb2);
}

you should use

StringBuilder sb1 = ..
for(..){
    //add all you want to sb1
    sb1.append(..)
    sb1.append(..)
}

Next thing is that you don't ever want to do

sb.appent("foo" + x + "bar");

because it is same as

sb.append(new StringBuilder("foo").append(x).append("bar").toString())

which is very ineffective because:

1. you are creating separate StringBuilder each time you do so
2. this new StringBuilder needs to unnecessary call toString method which has to copy all characters to new String which will later be copied to builder, instead of calling append(StringBuilder) and copy its characters directly.

So instead of sb.appent("foo" + x + "bar"); always write

sb.appent("foo").append(x).append("bar");

Now lets go back to your main problem. Since your code doesn't have declaration of line variable I am assuming that by

String[] abc = line.split("\t");

you mean

String[] abc = allLines.get(i).split("\t");

So your code can look like

StringBuilder temp = new StringBuilder();

for (int i = 0; i < allLines.size(); i++) {

    String[] abc = allLines.get(i).split("\t");

    temp.append("{id: \"").append(abc[0]).append("\", ");
    temp.append("name: \"").append(abc[1]).append("\"}");
    if (i < allLines.size() - 1)
        temp.append(", ");
}

System.out.println("result : " + temp.toString());

No Java 8 solution:

StringBuilder temp = new StringBuilder();
adder(temp, allLines.get(0));

for (int i=1; i<allLines.size(); i++){
     temp.append(",");
     adder(temp, allLines.get(i));
}
System.out.println("result : "+temp.toString());

private static void adder(StringBuilder temp,String line){
    String[] abc = line.split("\t");
    temp.append("{id: \"");
    temp.append(abc[0]);
    temp.append("\",");
    temp.append("name: \"");
    temp.append(abc[1]);
    temp.append("\"}");
}